JP4015228B2 - Circularly polarized light separating layer, optical element, polarized light source device, and liquid crystal display device - Google Patents

Description

（ただし、Ｒ¹は水素又はメチル基、ｍは１〜６の整数、Ｘ¹はＣＯ₂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、Ｒ²は水素又はメチル基、ｎは１〜６の整数、Ｘ²はＣＯ₂基又はＯＣＯ基、Ｘ³は−ＣＯ−Ｒ³又は−Ｒ⁴であり、そのＲ³は

Ｒ⁴は

であり、Ｒ⁵は下記のものである。）

【００２６】
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。その例としては、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一般式（ａ）に属するモノマーを得る方法があげれる。
【００２７】
また、一般式（ｂ）に属するアクリル系モノマーの合成例としては、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Ｒ³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方法や、前記の脱水反応後その（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方法などがあげられる。
【００２８】
従って、前記の一般式（ａ）や一般式（ｂ）に属する他のモノマーも、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。なお前記の４位にＲ³基含有のＣＯ基を有するフェノールは、例えば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−Ｒ³と反応させてＲ³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方法などにより、また４位に不斉炭素基を有するフェノールは、例えば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方法などにより得ることができる。
【００２９】
上記した共重合体は、その一般式（ｂ）で表わされるモノマー単位の含有率を変えることでコレステリック液晶の螺旋ピッチを変化させることができる。従って、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でき、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。
【００３０】
液晶ポリマーによるコレステリック液晶層の形成は、従来の配向処理に準じた方法で行うことができる。ちなみにその例としては、支持基材上にポリイミドやポリビニルアルコール、ポリエステルやポリアリレート、ポリアミドイミドやポリエーテルイミド等の膜を形成してレーヨン布等でラビング処理した配向膜、又はＳｉＯの斜方蒸着層、又は延伸処理による配向膜等からなる適宜な配向膜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。
【００３１】
前記の支持基材としては、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、アモルファスポリオレフィンや変性アクリル系ポリマー、エポキシ系樹脂の如きプラスチックからなる単層又は積層フイルム、あるいはガラス板などの適宜なものを用いうる。薄型化等の点よりは、プラスチックフィルムが好ましく、また偏光状態の変化の防止による光の利用効率の向上などの点よりは複屈折による位相差が可及的に小さいものが好ましい。
【００３２】
液晶ポリマーの展開は、例えば液晶ポリマーの溶媒による溶液をスピンコート法やロールコート法、フローコート法やプリント法、ディップコート法や流延成膜法、バーコート法やグラビア印刷法等の適宜な方法で薄層展開し、それを必要に応じ乾燥処理する方法などにより行うことができる。前記の溶媒としては、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。
【００３３】
また液晶ポリマーの加熱溶融物、好ましくは等方相を呈する状態の加熱溶融物を前記に準じ展開し、必要に応じその溶融温度を維持しつつ更に薄層に展開して固化させる方法などの、溶媒を使用しない方法、従って作業環境の衛生性等が良好な方法によっても液晶ポリマーを展開させることができる。なお液晶ポリマーの展開に際しては、薄型化等を目的に必要に応じて配向膜を介したコレステリック液晶層の重畳方式なども採ることができる。
【００３４】
液晶ポリマーの展開層を配向させるための加熱処理は、上記した如く液晶ポリマーのガラス転移温度から等方相転移温度までの温度範囲、すなわち液晶ポリマーが液晶相を呈する温度範囲に加熱することにより行うことができる。また配向状態の固定化は、ガラス転移温度未満に冷却することで行うことができ、その冷却条件については特に限定はない。通例、前記の加熱処理を３００℃以下の温度で行いうることから、自然冷却方式が一般に採られる。
【００３５】
支持基材上に形成した液晶ポリマーの固化層は、支持基材との一体物としてそのまま円偏光分離層に用いうるし、支持基材より剥離してフィルム等からなる円偏光分離層として用いることもできる。フィルム等からなる支持基材との一体物として形成する場合には、偏光の状態変化の防止性などの点より、位相差が可及的に小さい支持基材を用いることが好ましい。
【００３６】
コレステリック液晶層の厚さは、配向の乱れや透過率低下の防止、選択反射の波長範囲（反射波長域）の広さなどの点より、０．５〜５０μm、就中１〜３０μm、特に１．５〜１０μmが好ましい。また円偏光分離層の薄型化等の点より２層のコレステリック液晶層の合計厚が１〜５０μm、就中２〜３０μm、特に３〜１０μmであることが好ましい。さらに支持基材を有する場合には、その基材を含めた合計厚が２０〜２００μm、就中２５〜１５０μm、特に３０〜１００μmであることが好ましい。円偏光分離層の形成に際しては、コレステリック液晶層に安定剤や可塑剤、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。
【００３７】
本発明において用いる円偏光分離層は、例えば低分子量体からなるコレステリック液晶層をガラスやフィルム等の透明基材で挾持したセル形態、液晶ポリマーからなるコレステリック液晶層を透明基材で支持した形態、コレステリック液晶層の液晶ポリマーフィルムからなる形態、それらの形態物を適宜な組合せで重畳した形態などの適宜な形態とすることができる。
【００３８】
前記の場合、コレステリック液晶層をその強度や操作性などに応じて１層又は２層以上の支持基材で保持することもできる。２層以上の支持基材を用いる場合には、偏光の状態変化を防止する点などより例えば無配向のフィルムや、配向しても複屈折の小さいトリアセテートフィルムなどの如く位相差が可及的に小さいものが好ましく用いうる。薄型化等の点より好ましい形態は、透明基材で支持した形態や液晶ポリマーのフィルムからなる形態などである。
【００３９】
本発明による円偏光分離層は、ベース層となるコレステリック液晶層を反射光の中心波長が異なる組合せで２対以上含む状態に形成することもできる。なおコレステリック液晶層の重畳には、製造効率や薄膜化などの点より液晶ポリマーの使用が特に有利である。重畳処理は、単なる重ね置きや、粘着剤等の接着剤を介した接着などの適宜な方式を採ることができる。
【００４０】
本発明においては、円偏光分離層に対して拡散層や１／４波長板や偏光板等の適宜な光学層の１種又は２種以上を配置して種々の光学素子を形成することができる。その例を図２、図３、図４に示した。２が拡散層、３が１／４波長板、４が偏光板である。
【００４１】
拡散層は、上記したように斜め入射光を円偏光分離層のベース層で全反射させてなる戻り光の進路変更を目的とし、この場合には円偏光分離層の光源光入射側に設けられる。拡散層は、例えば粒子分散樹脂層の形成方式、サンドブラストや化学エッチング等の表面凹凸化処理による方式、機械的ストレスや溶剤処理等によるクレイズ発生方式、所定の拡散構造を設けた金型による転写形成方式などの任意な方式で、円偏光分離層への塗布層や拡散シートなどとして適宜に形成することができる。
【００４２】
また拡散層は、光学素子からの出射光を平準化して明暗ムラを抑制し、液晶セルに適用した場合に画素との干渉でモアレによるギラギラした視認が生じることの防止などを目的に配置することもできる。この場合には、円偏光分離層の１／４波長板付設側やそれに設けた１／４波長板や偏光板の間、あるいは偏光板の上面などの、円偏光分離層や１／４波長板や偏光板等に隣接した適宜な位置に１層又は２層以上を配置することができる。円偏光分離層より出射した光の偏光状態の維持性などの点より好ましく用いうる拡散層は、位相差が波長６３３nmの垂直入射光、好ましくは入射角３０度以内の入射光に基づいて３０nm以下、就中０〜２０nmのものである。
【００４３】
１／４波長板は、直線偏光変換手段として機能するものであり、円偏光分離層より出射した円偏光が１／４波長板に入射して位相変化を受け、その位相変化が１／４波長に相当する波長の光は直線偏光に変換され、他の波長光は楕円偏光に変換される。変換された楕円偏光は、前記の直線偏光に変換された光の波長に近いほど扁平な楕円偏光となる。かかる結果、偏光板を透過しうる直線偏光成分を多く含む状態の光が１／４波長板より出射されることとなる。
【００４４】
従って図例の如く１／４波長板３は、円偏光分離層１の光出射側に配置される。なおコレステリック液晶層が一方のベース層を除き反射光の中心波長の順序で重畳されているいる場合には、上記した波長シフトの抑制などの点よりその長波長のコレステリック液晶層側を光出射側とすることが好ましい。前記の如く１／４波長板を介して直線偏光成分の多い状態に変換することにより、偏光板を透過しやすい光とすることができる。この偏光板は、例えば液晶表示装置の場合、液晶セルに対する視野角の変化で発生する偏光特性の低下を防止して表示品位を維持する光学層や、より高度な偏光度を実現して、よりよい表示品位を達成する光学層などとして機能するものである。
【００４５】
すなわち前記において、偏光板を用いずに、円偏光分離層よりの出射偏光をそのまま液晶セルに入射させて表示を達成することは可能であるが、偏光板を介することで前記した表示品位の向上等をはかりうることから必要に応じて偏光板が用いられる。その場合に、偏光板に対する透過率の高いほど表示の明るさの点より有利であり、その透過率は偏光板の偏光軸（透過軸）と一致する偏光方向の直線偏光成分を多く含むほど高くなるので、それを目的に直線偏光変換手段を介して円偏光分離層よりの出射偏光を所定の直線偏光に変換するものである。
【００４６】
１／４波長板としては、円偏光分離層より出射した円偏光を、１／４波長の位相差に相当して直線偏光を多く形成しうると共に、他の波長の光を前記直線偏光と可及的にパラレルな方向に長径方向を有し、かつ可及的に直線偏光に近い扁平な楕円偏光に変換しうるものが好ましい。かかる１／４波長板を用いることにより、その出射光の直線偏光方向や楕円偏光の長径方向が偏光板の透過軸と可及的に平行になるように配置して、偏光板を透過しうる直線偏光成分の多い状態の光を得ることができる。
【００４７】
１／４波長板は、１層又は２層以上の位相差板の重畳層として形成することができる。１層の位相差板からなる１／４波長板の場合には、複屈折の波長分散が小さいものほど波長毎の偏光状態の均一化をはかることができて好ましい。一方、位相差板の重畳化は、波長域における波長特性の改良に有効であり、その組合せは波長域などに応じて適宜に決定してよい。
【００４８】
ちなみに可視光域の光に対し波長範囲や変換効率等の点より好ましく用いうる単層型の１／４波長板としては、その位相差が小さいもの、就中１００〜１８０nm、特に１１０〜１５０nm以下の位相差を与えるものである。また２層以上の位相差板からなる１／４波長板とする場合には、１００〜１８０nmの位相差を与える層を１層以上の奇数層で含む、２００nm以上の位相差を与える層との組合せとすることが波長特性等の点より好ましい。
【００４９】
１／４波長板を形成する位相差板は、適宜な材質で形成でき、透明で均一な位相差を与えるものが好ましい。一般には、例えばポリカーボネートやポリスルホン、ポリエステルやポリメチルメタクリレート、ポリアミドやポリビニールアルコール等の適宜なプラスチック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などが用いられる。
【００５０】
上記の図４に例示の如く１／４波長板３の上には必要に応じて偏光板４を設けることができる。かかる形態の光学素子は、その偏光板を液晶セルの光源側の偏光板として利用することができる。また偏光板は、円偏光分離層に１／４波長板を介することなく配置してもよく、この場合には円偏光分離層を透過した円偏光を偏光板を介し直接直線偏光化する。
【００５１】
偏光板としては、適宜なものを用いうるが一般には、偏光フィルムからなるものが用いられる。偏光フィルムの例としては、ポリビニルアルコール系や部分ホルマール化ポリビニルアルコール系、エチレン・酢酸ビニル共重合体系部分ケン化物の如き親水性高分子のフィルムにヨウ素等の二色性染料を吸着させて延伸したもの、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の如きポリエン配向フィルムなどがあげられる。
【００５２】
円偏光分離層に付設する偏光板としては、二色性染料を含有するタイプのものが偏光度等の点より特に好ましく用いられる。偏光フィルムの厚さは通例５〜８０μmであるが、これに限定されない。用いる偏光板は、偏光フィルムの片面又は両面を透明保護層等で被覆したものなどであってもよい。
【００５３】
本発明による円偏光分離層や光学素子は、偏光光源装置の形成に好ましく用いうる。偏光光源装置の形成は、光源の上に円偏光分離層や光学素子を配置することにより行うことができる。なお図２の如く外表面に拡散層２を有する光学素子の場合にはその拡散層側に光源が配置され、図３や図４の如く円偏光分離層が１／４波長板３等を有する場合には、その１／４波長板等を有しない側に光源が配置される。
【００５４】
図５に偏光光源装置５の例を示した。これは、円偏光分離層を光学素子として用いた場合を示しており、５１が導光板、５２が光源である。導光板５１は、側面に配置した光源５２からの入射光を上面（円偏光分離層側）より出射して光源５２と一体的に機能し、円偏光分離層に対して光を供給する光源として機能するものである。
【００５５】
前記の偏光光源装置５によれば、光源５２からの入射光が導光板５１の上面より出射し、その垂直方向の光は、出射面側に配置した円偏光分離層１に入射して左右一方の円偏光が透過し、他方の円偏光が反射されて戻り光として導光板５１に再入射する。導光板に再入射した光は、下面の反射層５４で反射されて再び円偏光分離層１に入射し、透過光と反射光（再々入射光）に再度分離される。
【００５６】
一方、円偏光分離層１に斜め入射して上記したベース層で全反射された戻り光も、導光板下面の反射層５４に入射して反射され、再び拡散層２を介して円偏光分離層１に入射する。その場合、再入射光の一部は拡散層２を介した拡散で円偏光分離層に垂直入射しうる光に変換され、前記した垂直方向の光と同様に挙動する。残る光は、再び斜め入射光として挙動する。従って斜め入射光の戻り光の内、拡散で円偏光分離層に垂直入射しうる光に変換される割合が多いほど正面輝度を向上させることができる。
【００５７】
上記のように偏光光源装置における光源としては、光利用効率の向上などの点より、側面に配置した光源からの入射光を上下面の一方より出射する導光板型のものが好ましく用いられる。その導光板としては、適宜なものを用いうるが一般には、いずれか一方が出射面となる上下面、及び上下面間の少なくとも一側面からなる入射面を有する板状物からなるものが用いられる。
【００５８】
導光板の形態は、出射面よりの出射効率に優れその出射光が出射面に対する垂直性に優れて有効利用しやすく、また円偏光分離層を介した再入射光の出射効率にも優れてその出射方向の初期出射方向との近似性などの点より、微細なプリズム状凹凸、就中、長辺面と短辺面からなる凸部又は凹部を周期的に有する構造が好ましい（特願平７−３２１０３６号）。さらに入射面に対向する側端部の厚さが入射面のそれよりも薄いもの、就中５０％以下の厚さであるものが好ましい。
【００５９】
前記の入射面に対する対向側端部の薄型化は、入射面より入射した光が伝送端としての当該対向側端部に至るまでに、プリズム状凹凸面の短辺面に効率よく入射し、その反射を介し出射面より出射して入射光を目的面に効率よく供給できる点で有利である。またかかる薄型化構造とすることで導光板を軽量化でき、例えばプリズム状凹凸面が直線状の場合、均一厚の導光板の約７５％の重量とすることができる。
【００６０】
プリズム状凹凸面における凸部又は凹部のピッチは、出射光がその凸部又は凹部を介し通例ストライプ状に放出されるため明暗ムラの抑制や液晶セルとのモアレの防止などの点より小さいほど好ましい。製造精度等を考慮した好ましい凸部又は凹部の周期は、５００μm以下、就中３００μm以下、特に５〜２００μmである。
【００６１】
導光板は、光源の波長領域に応じそれに透明性を示す適宜な材料にて形成しうる。ちなみに可視光域では、例えばポリメチルメタクリレートの如きアクリル系樹脂、ポリカーボネートやポリカーボネート・ポリスチレン共重合体の如きポリカーボネート系樹脂、エポキシ系樹脂等で代表される透明樹脂やガラスなどの如く約４００〜７００nmの波長範囲で透明性を示すものがあげられる。
【００６２】
導光板は、適宜な方法で形成したものであってよい。量産性等の点より好ましい製造方法としては、例えば熱や紫外線ないし放射線等で重合処理しうる液状樹脂を、所定のプリズム状凹凸を形成しうる型に充填ないし流延して重合処理する方法や、熱可塑性樹脂を所定のプリズム状凹凸を形成しうる金型に加熱下に押付けて形状を転写する方法、加熱溶融させた熱可塑性樹脂あるいは熱や溶媒を介して流動化させた樹脂を所定の形状に成形しうる金型に充填する射出成形等の方法などがあげられる。
【００６３】
導光板は、例えば光の伝送を担う導光部にプリズム状凹凸面形成用のシートを接着したものの如く、異種材料の積層体などとして形成されていてもよく、１種の材料による一体的単層物として形成されている必要はない。上記した導光板では、短辺面と長辺面の面積比や傾斜角、プリズム状凹凸面の形状や曲率等の制御に基づいて出射光の角度分布や面内分布等の特性を調節することができる。
【００６４】
導光板の厚さは、使用目的による導光板のサイズや光源の大きさなどにより適宜に決定することができる。液晶表示装置等に用いる場合の導光板の一般的な厚さは、その入射面に基づき２０mm以下、就中０．１〜１０mm、特に０．５〜８mmである。
【００６５】
導光板の出射面の対向面に配置する反射層５４は、メッキ層や金属蒸着層、金属箔や金属蒸着シート、メッキシートなどにより適宜に形成でき、導光板の当該対向面に一体化されていてもよいし、反射シート等として重ね合されていてもよく、本発明にては適宜な配置形態を採ることができる。反射を介して円偏光を反転させる点よりは金属反射面が好ましい。
【００６６】
また反射層の表面に例えば微細凹凸構造を付与するなどして光拡散型の反射層とした場合には、円偏光分離層のベース層を介して全反射させた戻り光を拡散させるための拡散層を省略した形態の偏光光源装置とすることもできる。この場合には、当該光拡散型の反射層に前記戻り光の拡散による進路変更を兼ねさせることができる。
【００６７】
導光板型の光源は、図５に例示の如く通例、導光板５１の入射面に光源５２を配置することにより形成される。その光源としては適宜なものを用いうるが、例えば（冷，熱）陰極管等の線状光源や発光ダイオード等の点光源、あるいはその線状又は面状等のアレイ体などが好ましく用いうる。当該バックライトの形成に際しては、必要に応じて図例の如く、線状光源からの発散光を導光板の側面に導くために光源を包囲する光源ホルダ５３や、光の出射方向制御用のプリズムシートなどの適宜な補助手段を配置した組合せ体とすることもできる。
【００６８】
偏光光源装置の形成に好ましく用いうる導光板は、側面よりの入射光を高い効率で出射面より出射させ、その出射光が高い指向性、就中、出射面に対する垂直性に優れる指向性を示すと共に、円偏光分離層を介した再入射光の再出射効率に優れ、その再出射光の指向性と出射角度が初期出射光の指向性と出射角度に可及的に一致し、かつ円偏光分離層を介した再入射光を少ない反射繰返し数で、就中、反射の繰返しなく出射するようにしたものである。
【００６９】
上記のように本発明による偏光光源装置は、円偏光分離層による反射光（再入射光）を偏光変換による出射光として再利用することで反射ロス等を防止し、その出射光を必要に応じ１／４波長板等を介し直線偏光成分をリッチに含む光状態に変換して偏光板を透過しやすくし吸収ロスを防止すると共に、円偏光分離層のベース層を介して全反射させた戻り光の一部を拡散により進路変更させて円偏光分離層より再度出射させて光利用効率の向上、特に正面輝度の向上を図るようにしたものである。
【００７０】
従って本発明による偏光光源装置は、上記の如く光の利用効率に優れて明るく、出射光の垂直性に優れて明暗ムラの少ない光を提供し、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種々の装置に好ましく用いることができる。
【００７１】
図６に本発明による偏光光源装置５をバックライトシステムに用いた液晶表示装置６を例示した。６１が液晶セル、６２が上側の偏光板、６３が拡散板である。下側の偏光板４や拡散板６３は必要に応じて設けられる。液晶表示装置は一般に、液晶シャッタとして機能する液晶セルとそれに付随の駆動装置、偏光板、バックライト、及び必要に応じての補償用位相差板等の構成部品を適宜に組立てることなどにより形成される。本発明においては、上記した偏光光源装置を用いる点を除いて特に限定はなく、従来に準じて形成することができる。特に、直視型の液晶表示装置を好ましく形成することができる。
【００７２】
従って用いる液晶セルについては特に限定はなく、適宜なものを用いうる。就中、偏光状態の光を液晶セルに入射させて表示を行うものに有利に用いられ、例えばツイストネマチック液晶やスーパーツイストネマチック液晶を用いた液晶セル等に好ましく用いうるが、非ツイスト系の液晶や二色性染料を液晶中に分散させたゲストホスト系の液晶、あるいは強誘電性液晶を用いた液晶セルなどにも用いうる。液晶の駆動方式についても特に限定はない。
【００７３】
なお高度な直線偏光の入射による良好なコントラスト比の表示を得る点よりは偏光板として、特にバックライト側の偏光板として、上記した如く例えばヨウ素系や染料系の吸収型直線偏光子などの如く偏光度の高いものを用いた液晶表示装置が好ましい。液晶表示装置の形成に際しては、例えば視認側の偏光板の上に設ける拡散板やアンチグレア層、反射防止膜や保護層や保護板、あるいは液晶セルと偏光板の間に設ける補償用位相差板などの適宜な光学層を適宜に配置することができる。
【００７４】
前記の補償用位相差板は、複屈折の波長依存性などを補償して視認性の向上等をはかることを目的とするものである。本発明においては、視認側又は／及びバックライト側の偏光板と液晶セルの間等に必要に応じて配置される。なお補償用位相差板としては、波長域などに応じて適宜なものを用いることができ、１層又は２層以上の重畳層として形成されていてよい。補償用位相差板は、上記した直線偏光変換用の位相差板で例示の延伸フィルムなどとして得ることができる。
【００７５】
本発明において、上記した偏光光源装置や液晶表示装置を形成する光学素子ないし部品は、全体的又は部分的に積層一体化されて固着されていてもよいし、分離容易な状態に配置したものであってもよい。
【００７６】
【実施例】
参考例
ガラス転移温度が異なる４種のアクリル系主鎖の側鎖型コレステリック液晶ポリマーを、厚さ３０μmのトリアセチルセルロースフィルムのポリイミドラビング処理面にスピンコート方式で成膜後（厚さ２μm）、所定温度に加熱して急冷し、鏡面状の選択反射状態を呈して左円偏光を透過し、選択反射の中心波長が４７０nm、５５０nm、６４０nm又は７７０nmである４種のコレステリック液晶層を得た。
【００７７】
実施例１
参考例で得た選択反射の中心波長が６４０nmのコレステリック液晶層からなるベース層の間に、選択反射の中心波長が４７０nmと５５０nmのコレステリック液晶層を配置して接着積層し、円偏光分離板を得た。
【００７８】
次に、前記の円偏光分離板における選択反射の中心波長が５５０nmのコレステリック液晶層に近い側に、正面位相差が１４０nmの１／４波長板を接着し、その１／４波長板の上に直線偏光面に透過軸を一致させて偏光板を接着し、光学素子を得た。
【００７９】
実施例２
実施例１に準じて、選択反射の中心波長が４７０nm、５５０nm、６４０nm、４７０nm、５５０nm、６４０nmの６層のコレステリック液晶層を当該順序で順次積層した円偏光分離板を得、それを用いて光学素子を得た。
【００８０】
実施例３
実施例１に準じて、選択反射の中心波長が４７０nm、５５０nm、６４０nm、７７０nm、４７０nm、５５０nm、６４０nmの７層のコレステリック液晶層を当該順序で順次積層した円偏光分離板を得、それを用いて光学素子を得た。
【００８１】
比較例１
実施例１に準じて、選択反射の中心波長が４７０nm、５５０nm、６４０nmの３層のコレステリック液晶層を当該順序で順次積層した円偏光分離板を得、それを用いて光学素子を得た。
【００８２】
比較例２
実施例１に準じて、選択反射の中心波長が４７０nm、５５０nm、６４０nm、７７０nmの４層のコレステリック液晶層を当該順序で順次積層した円偏光分離板を得、それを用いて光学素子を得た。
【００８３】
評価試験
下面に微細プリズム構造を形成した導光板の側面に直径３mmの冷陰極管を配置し、銀蒸着のポリエステルフィルムからなる光源ホルダにて冷陰極管を包囲し、導光板の下面に銀蒸着のポリエステルフィルムからなる反射シートを配置してなるサイドライト型の面光源装置の上面に、シリカ粒子を含有して表面が微細凹凸構造の拡散シートを配置し、その上に実施例、比較例で得た光学素子をその偏光板を上側にして配置し、偏光光源装置を得た。
【００８４】
次に、前記の偏光光源装置における偏光板の上面に、市販のＴＦＴ型液晶パネルを配置して液晶表示装置を得、輝度計（トプコン社製、ＢＭ−５）を用いてバックライト点灯時のパネル垂直方向における正面輝度を調べた。結果を次表に示した。
【００８５】

【図面の簡単な説明】
【図１】円偏光分離層例の断面図
【図２】光学素子例の断面図
【図３】他の光学素子例の断面図
【図４】さらに他の光学素子例の断面図
【図５】偏光光源装置例の断面図
【図６】液晶表示装置例の断面図
【符号の説明】
１：円偏光分離層
１１，１３：コレステリック液晶層からなるベース層
１２，１４：偏光状態を変化させる媒体
１５，１６：コレステリック液晶層からなる外部配置層
２：拡散層
３：１／４波長板
４：偏光板
５：偏光光源装置
５１：導光板
５２：光源
５４：反射層
６：液晶表示装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a circularly polarized light separation layer that can form a high-luminance polarized light source device or a highly visible liquid crystal display device with excellent light utilization efficiency, and an optical element using the same.
[0002]
[Background]
Conventionally, there has been known a polarized light source using a circularly polarized light separation layer composed of a cholesteric liquid crystal layer that separates natural light into left and right circularly polarized light through reflection and transmission (Japanese Patent Laid-Open Nos. 59-27019 and 61). JP-A-122626, JP-A-63-121821, JP-A-3-45906, JP-A-6-324333, JP-A-7-35925, JP-A-7-36025. , JP-A-7-36032).
[0003]
However, although light incident perpendicularly (front) to the circularly polarized light separating layer is transmitted as one of the left and right circularly polarized light, obliquely incident light is transmitted as elliptically polarized light, which is also circularly polarized even through a quarter-wave plate. As described above, in order to maintain the elliptically polarized state without being linearly polarized, there is a problem that the light utilization efficiency is poor because it contains a component absorbed by the polarizing plate.
[0004]
In addition, the elliptically polarized light obliquely transmitted through the circularly polarized light separating layer is subjected to a color change, so that when applied to a liquid crystal display device or the like, the elliptically polarized light becomes light that reduces visibility as a color change due to a viewing angle change, and is emitted vertically from the circularly polarized light separating layer. Thus, there is a problem that the liquid crystal display device does not contribute to the improvement of the front luminance effective for ensuring good visual recognition.
[0005]
[Technical Problem of the Invention]
The present invention is a circularly polarized light that can reduce obliquely transmitted elliptically polarized light and can convert the elliptically polarized light into light that can contribute to improved frontal brightness without harming the transmitted circularly polarized light characteristic of normal incident light that contributes to the front brightness. The task is to develop a separation layer.
[0006]
[Means for solving problems]
The present invention provides a circularly polarized light separating layer characterized in that a medium for changing the polarization state is disposed between base layers composed of cholesteric liquid crystal layers having a difference in center wavelength of reflected light within 20 nm. .
[0007]
【The invention's effect】
According to the present invention, the normal incident light is vertically transmitted through each superimposed cholesteric liquid crystal layer as the predetermined circularly polarized light, thereby contributing to the improvement of the front luminance. On the other hand, elliptically polarized light that is obliquely transmitted through the base layer on one side and obliquely incident on the medium that changes the polarization state undergoes polarization characteristic conversion by transmitting through the medium, and the rotation direction of some of the polarized light is reversed. Thus, the light is totally reflected when obliquely incident on the next base layer, and the transmission of the circularly polarized light separating layer is blocked. As a result, oblique transmission elliptical polarization that reduces visibility as a color change due to a change in viewing angle when applied to a liquid crystal display device or the like is reduced without impairing the transmission circular polarization characteristics of vertically incident light that contributes to front luminance. be able to.
[0008]
On the other hand, the polarized light that has been totally reflected as described above is transmitted through the base layer on the incident side again when the light is transmitted again through the medium that changes the polarization state as return light, and is emitted from the circularly polarized light separating layer. The emitted light is reflected through the reflective layer and incident again on the circularly polarized light separating layer, and is diffused through the diffusing layer in the meantime, so that a part of the emitted light is vertically incident on the circularly polarized light separating layer and light in the front direction. Can be taken out as. As a result, the elliptically polarized light obliquely transmitted through one base layer is blocked by total reflection by the other base layer, and the total reflected light is reused to improve the visibility of liquid crystal display devices and the like from the circularly polarized light separating layer. Light in the front direction can be obtained, and the front luminance can be improved. As a result, it is possible to form a polarized light source device that is excellent in light utilization efficiency, particularly excellent in front luminance, using such a circularly polarized light separation layer, and is bright and visible in combination with a quarter-wave plate or a polarizing plate. Can be obtained.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The circularly polarized light separating layer of the present invention is formed by disposing a medium for changing the polarization state between base layers made of cholesteric liquid crystal layers having a difference in center wavelength of reflected light within 20 nm. The example is shown to Fig.1 (a)-(d). 1 is a circularly polarized light separating layer, 11 and 13 are base layers, 12 and 14 are media for changing the polarization state, and 15 and 16 are cholesteric liquid crystal layers arranged outside.
[0010]
As the cholesteric liquid crystal layer, an appropriate layer can be used that separates natural light into transmitted and reflected light and left and right circularly polarized light by Grandjean alignment. Incidentally, specific examples include a layer having a cholesteric liquid crystal phase, a sheet having a layer composed of a liquid crystal polymer exhibiting a cholesteric phase, a sheet obtained by spreading the layer on a glass plate, or a liquid crystal polymer exhibiting a cholesteric phase. Film. Therefore, the cholesteric liquid crystal layer may be superposed in a state where it is supported on a support base material as necessary.
[0011]
In the above, the cholesteric liquid crystal layer is preferably aligned as uniformly as possible. Uniformly oriented cholesteric liquid crystal layers provide reflected light without scattering, which is advantageous for widening the viewing angle of liquid crystal display devices and the like, especially for the formation of direct-view liquid crystal display devices and the like that can be directly observed from an oblique direction. Is suitable.
[0012]
The circularly polarized light separating layer according to the present invention can be formed by arranging and superposing a medium that changes the polarization state between base layers made of cholesteric liquid crystal layers having a difference in center wavelength of reflected light within 20 nm. . As a result, a part of the light obliquely transmitted through one base layer can be totally reflected through the other base layer. The difference in the center wavelength of the reflected light between the base layers, which is preferable in view of the achievement of total reflection, is within 15 nm, in particular within 10 nm, particularly within 5 nm. If the difference in the center wavelength of the reflected light exceeds 20 nm, it becomes difficult to form a base layer relationship that satisfies the total reflection condition, and oblique incident light is easily transmitted.
[0013]
As the medium for changing the polarization state disposed between the base layers, an appropriate medium that can change the polarization state such as a retardation plate such as a quarter-wave plate or a half-wave plate can be used. In particular, a cholesteric liquid crystal layer, particularly a cholesteric liquid crystal layer in which the central wavelength of reflected light is different from that of at least one base layer by 80 nm or more is preferable from the viewpoint of expanding the wavelength range of transmitted light. In other words, a single-layer cholesteric liquid crystal layer usually has a limit in the wavelength range showing selective reflectivity (circular dichroism), and the limit may be a wide range extending to a wavelength range of about 100 nm. However, since it does not reach the entire visible light range that is desired when applied to liquid crystal display devices, etc., the wavelength range showing circular dichroism is expanded by overlapping cholesteric liquid crystal layers with different selective reflectivities (reflection wavelength ranges). Thus, a cholesteric liquid crystal layer can be preferably used from the viewpoint that the entire visible light region or the entire visible wavelength region is made a reflection wavelength region.
[0014]
The medium for changing the polarization state disposed between the base layers may be one layer or two or more layers. When two or more cholesteric liquid crystal layers are arranged as a medium for changing the polarization state between the base layers, a combination of cholesteric liquid crystal layers having different reflection wavelength ranges, and in particular, the center wavelength of the reflected light, from the above points. Is preferred. An appropriate light transmission layer other than the medium that changes the polarization state may be disposed between the base layers, and the light transmission layer may be an optical functional layer.
[0015]
As a medium for changing the polarization state, a half-wave plate function is exhibited for obliquely transmitted light because a part of light obliquely transmitted through one base layer is totally reflected through the other base layer. Those are preferred. Such a half-wave plate function may be achieved in part or all of the medium that changes the polarization state placed between the base layers. That is, when the medium for changing the polarization state is a single layer, the one layer is required to exhibit a half-wave plate function. However, when the medium for changing the polarization state is two or more layers, Each layer or two or more layers may exhibit a half-wave plate function, or two or more layers may exhibit a half-wave plate function as a whole.
[0016]
The expansion of the reflection wavelength region due to the superposition of the cholesteric liquid crystal layer described above is such that the center wavelength of the reflected light is 80 nm or more with that of the base layer outside the base layers 11 and 13 as illustrated in FIGS. 1 (c) and 1 (d). This can also be achieved by a system in which different cholesteric liquid crystal layers 15 and 16 are arranged. In that case, the cholesteric liquid crystal layer can have one layer or two or more layers superimposed on one or both of the base layers. Also in this case, when two or more cholesteric liquid crystal layers in total are superposed on one or both of the base layers, it is preferable to use a combination of those having different reflection wavelength ranges, particularly, center wavelengths of reflected light.
[0017]
In the above, the superposed cholesteric liquid crystal layer has the same direction from the point that the phase state of the circularly polarized light reflected by each layer is aligned to prevent different polarization states in each wavelength region and the amount of polarized light in the usable state is increased. In order to achieve total reflection between the base layers, it is necessary to use a combination of those that reflect circularly polarized light in the same direction. The cholesteric liquid crystal layer is preferably superposed in the wavelength order based on the center wavelength of the reflected light except for one base layer, from the viewpoint of suppressing wavelength shift at a large viewing angle.
[0018]
A suitable cholesteric liquid crystal may be used without any particular limitation. Accordingly, various types such as a main chain type and a side chain type in which a conjugated linear atomic group (mesogen) imparting liquid crystal alignment is introduced into the main chain or side chain of the polymer can be used. A cholesteric liquid crystal molecule having a larger phase difference has a wider selective reflection wavelength range, and can be preferably used from the viewpoint of a margin for wavelength shift at a large viewing angle. A liquid crystal polymer can be preferably used from the viewpoint of weight, self-supporting property, and the like. Furthermore, as the liquid crystal polymer, those having a glass transition temperature of 30 to 150 ° C. can be preferably used from the viewpoints of handleability and stability of alignment at practical temperatures.
[0019]
By the way, examples of the main chain type liquid crystal polymer described above have a structure in which a mesogenic group composed of a para-substituted cyclic compound or the like is bonded via a spacer portion that imparts flexibility, for example, a polyester type or a polyamide type. And polymers such as polycarbonate and polyesterimide.
[0020]
Examples of the side chain type liquid crystal polymer include polyacrylate, polymethacrylate, polysiloxane, polymalonate, etc. as the main chain skeleton, and a para-substituted cyclic group through a spacer portion composed of a conjugated atomic group as the side chain. Examples thereof include those having a low molecular liquid crystal compound (mesogen part) composed of a compound, a nematic liquid crystal polymer containing a low molecular chiral agent, a liquid crystal polymer having a chiral component introduced therein, and a mixed liquid crystal polymer of nematic and cholesteric types.
[0021]
As described above, for example, a paraffin that imparts a nematic orientation comprising a para-substituted aromatic unit such as an azomethine form, an azo form, an azoxy form, an ester form, a biphenyl form, a phenylcyclohexane form, or a bicyclohexane form, or a para-substituted cyclohexyl ring unit. Even those having a substituted cyclic compound can be made cholesteric oriented by a method of introducing an appropriate chiral component made of a compound having an asymmetric carbon, a low molecular chiral agent, or the like (JP-A-55). No. 21479, US Pat. No. 5,332,522, etc.). The terminal substituent at the para position in the para-substituted cyclic compound may be an appropriate one such as a cyano group, an alkyl group, or an alkoxy group.
[0022]
As the spacer portion, for example, polymethylene chain-(CH ₂ ) _n -Or polyoxymethylene chain-(CH ₂ CH ₂ O) _m -And the like. The number of repeating structural units forming the spacer portion is appropriately determined depending on the chemical structure of the mesogen portion, etc. Generally, in the case of a polymethylene chain, n is 0 to 20, especially 2 to 12, and in the case of a polyoxymethylene chain M is 0-10, especially 1-3.
[0023]
The main chain type liquid crystal polymer can be prepared by an appropriate method according to a usual polymer synthesis, for example, by copolymerizing component monomers by a radical polymerization method, a cationic polymerization method, an anionic polymerization method, or the like. In addition, preparation of side chain type liquid crystal polymer is also possible by, for example, polymerizing a monomer having a mesogenic group introduced through a spacer group into a monomer for forming a vinyl main chain such as an ester of acrylic acid or methacrylic acid by a radical polymerization method or the like. Monomer addition polymerization method, addition reaction of vinyl-substituted mesogenic monomer in the presence of platinum-based catalyst via Si-H bond of polyoxymethylsilylene, and phase transfer catalyst via functional group attached to main chain polymer The mesogenic group may be introduced by a suitable esterification reaction or by a polycondensation reaction between a monomer having a mesogenic group introduced into a part of malonic acid via a spacer group and a diol if necessary. Can do.
[0024]
In the above, film formability, good monodomain Grandian orientation, short-time orientation processing, stable fixation to the glass state, controllability of the cholesteric phase helical pitch, thin and light orientation such as pitch The liquid crystal polymer that can be preferably used in view of the formability of a circularly polarized light separating layer that is hardly changed at practical temperature and has excellent durability and storage stability, includes a monomer unit represented by the following general formula (a), A copolymer comprising monomer units represented by the formula (b) as a component, particularly comprising 60 to 95% by weight of the monomer units of the general formula (a) and 40 to 5% by weight of the monomer units of the general formula (b). A copolymer is used as a component (Japanese Patent Application No. 7-251818).
[0025]
General formula (a):

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

(However, R ² Is hydrogen or a methyl group, n is an integer of 1-6, X ² Is CO ₂ Group or OCO group, X ^Three Is -CO-R ^Three Or -R ^Four And its R ^Three Is

R ^Four Is

And R ^Five Is the following: )

[0026]
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. As an example, first, ethylene chlorohydrin and 4-hydroxybenzoic acid were heated to reflux in an alkaline aqueous solution using potassium iodide as a catalyst to obtain a hydroxycarboxylic acid, which was then subjected to a dehydration reaction 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). The method of obtaining the monomer which belongs to is mentioned.
[0027]
In addition, as an synthesis example of the acrylic monomer belonging to the general formula (b), first, hydroxyalkyl halide and 4-hydroxybenzoic acid were heated to reflux in an alkaline aqueous solution using potassium iodide as a catalyst to obtain hydroxycarboxylic acid. After that, it is dehydrated with acrylic acid or methacrylic acid to give (meth) acrylate, and the (meth) acrylate is R-positioned to the 4-position. ^Three A method of esterifying with a phenol having a group-containing CO group in the presence of DCC and DMAP, or a phenol having an asymmetric carbon group at the 4-position after the dehydration reaction in the presence of DCC and DMAP. And the like.
[0028]
Therefore, other monomers belonging to the above general formula (a) or general formula (b) can also be synthesized according to the above using appropriate raw materials having the target introduction group. In the 4th place, R ^Three The phenol having a group-containing CO group is obtained by, for example, first reacting methyl chloroformate and 4-hydroxybenzoic acid in an aqueous alkaline solution to form a carboxylic acid, which is converted to an acid chloride with oxalyl chloride, and then H 2 in pyridine / tetrahydrofuran. -R ^Three React with R ^Three For example, phenol having an asymmetric carbon group at the 4-position can be obtained by, for example, treating 4-hydroxybenzaldehyde with (S)-(-)- It can be obtained by a method of azeotropic dehydration of 1-phenylethylamine in toluene.
[0029]
The above-mentioned copolymer can change the helical pitch of the cholesteric liquid crystal by changing the content of the monomer unit represented by the general formula (b). Therefore, the wavelength exhibiting circular dichroism can be adjusted by controlling the content of the monomer unit represented by the general formula (b), and an optical element exhibiting circular dichroism with respect to light in the visible light range can be easily obtained. Obtainable.
[0030]
Formation of the cholesteric liquid crystal layer by the liquid crystal polymer can be performed by a method according to a conventional alignment treatment. Incidentally, as an example, an alignment film formed by forming a film of polyimide, polyvinyl alcohol, polyester, polyarylate, polyamide imide, polyether imide or the like on a supporting substrate and rubbing with a rayon cloth or the like, or oblique deposition of SiO The liquid crystal polymer is spread on an appropriate alignment film composed of a layer or an alignment film by stretching treatment, and heated to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature. Examples thereof include a method of forming a solidified layer in which the orientation is fixed by cooling to below the transition temperature to form a glass state.
[0031]
Examples of the supporting substrate include triacetyl cellulose and polyvinyl alcohol, polyimide and polyarylate, polyester and polycarbonate, polysulfone and polyethersulfone, amorphous polyolefin, modified acrylic polymer, and a single layer made of plastic such as epoxy resin. An appropriate film such as a laminated film or a glass plate can be used. A plastic film is preferable from the viewpoint of thinning and the like, and a film having a phase difference due to birefringence as small as possible is preferable from the viewpoint of improving light utilization efficiency by preventing a change in polarization state.
[0032]
The development of the liquid crystal polymer may be carried out by appropriately applying a solution of the liquid crystal polymer in a solvent such as a spin coating method, a roll coating method, a flow coating method, a printing method, a dip coating method, a casting film forming method, a bar coating method or a gravure printing method. A thin layer can be developed by a method, and a drying process can be performed as necessary. As said solvent, suitable things, such as a methylene chloride, cyclohexanone, trichloroethylene, tetrachloroethane, N-methylpyrrolidone, tetrahydrofuran, etc. can be used, for example.
[0033]
Further, a heating melt of the liquid crystal polymer, preferably a heating melt in a state of exhibiting an isotropic phase, is developed according to the above, and further, a method of developing into a thin layer and solidifying while maintaining the melting temperature as required, etc. The liquid crystal polymer can also be developed by a method that does not use a solvent, that is, a method that provides good working environment hygiene. In developing the liquid crystal polymer, a superimposing method of a cholesteric liquid crystal layer through an alignment film can be adopted as necessary for the purpose of thinning.
[0034]
The heat treatment for aligning the spread layer of the liquid crystal polymer is performed by heating to a temperature range from the glass transition temperature to the isotropic phase transition temperature of the liquid crystal polymer, that is, a temperature range in which the liquid crystal polymer exhibits a liquid crystal phase as described above. be able to. In addition, the alignment state can be fixed by cooling below the glass transition temperature, and the cooling conditions are not particularly limited. Usually, since the heat treatment can be performed at a temperature of 300 ° C. or less, a natural cooling method is generally adopted.
[0035]
The solidified layer of the liquid crystal polymer formed on the support substrate can be used as it is in the circularly polarized light separation layer as an integral part of the support substrate, or it can be used as a circularly polarized light separation layer made of a film or the like by peeling from the support substrate. it can. In the case of forming it as an integral body with a supporting substrate made of a film or the like, it is preferable to use a supporting substrate having a phase difference as small as possible from the viewpoint of preventing polarization state change.
[0036]
The thickness of the cholesteric liquid crystal layer is 0.5 to 50 μm, especially 1 to 30 μm, particularly 1 from the viewpoints of preventing disorder of alignment and a decrease in transmittance and the wide wavelength range (reflection wavelength range) of selective reflection. 5 to 10 μm is preferable. In view of reducing the thickness of the circularly polarized light separating layer, the total thickness of the two cholesteric liquid crystal layers is preferably 1 to 50 μm, more preferably 2 to 30 μm, and particularly preferably 3 to 10 μm. Furthermore, when it has a support base material, it is preferable that the total thickness including the base material is 20-200 micrometers, especially 25-150 micrometers, especially 30-100 micrometers. When forming the circularly polarized light separating layer, various additives such as stabilizers, plasticizers or metals can be blended in the cholesteric liquid crystal layer as necessary.
[0037]
The circularly polarized light separating layer used in the present invention is, for example, a cell form in which a cholesteric liquid crystal layer made of a low molecular weight material is held by a transparent substrate such as glass or a film, a form in which a cholesteric liquid crystal layer made of a liquid crystal polymer is supported by a transparent substrate, Appropriate forms such as a form made of a liquid crystal polymer film of a cholesteric liquid crystal layer and a form in which those forms are superimposed in an appropriate combination can be adopted.
[0038]
In the above case, the cholesteric liquid crystal layer can be held by a supporting substrate of one layer or two or more layers according to its strength, operability and the like. When using a support substrate of two or more layers, the phase difference is made as much as possible, such as a non-oriented film or a triacetate film having a small birefringence even when oriented, in view of preventing changes in the state of polarized light. Small ones can be preferably used. A form preferable from the viewpoint of thinning and the like includes a form supported by a transparent substrate and a form made of a liquid crystal polymer film.
[0039]
The circularly polarized light separating layer according to the present invention can also be formed in a state including two or more pairs of cholesteric liquid crystal layers serving as a base layer in combinations with different center wavelengths of reflected light. For superimposing the cholesteric liquid crystal layer, it is particularly advantageous to use a liquid crystal polymer from the viewpoints of production efficiency and thinning. The superimposition process can take an appropriate method such as simple stacking or bonding via an adhesive such as a pressure-sensitive adhesive.
[0040]
In the present invention, various optical elements can be formed by arranging one type or two or more types of appropriate optical layers such as a diffusion layer, a quarter-wave plate and a polarizing plate with respect to the circularly polarized light separating layer. . Examples thereof are shown in FIGS. 2, 3, and 4. 2 is a diffusion layer, 3 is a quarter wavelength plate, and 4 is a polarizing plate.
[0041]
The diffusion layer is intended to change the path of return light obtained by totally reflecting obliquely incident light by the base layer of the circularly polarized light separating layer as described above, and in this case, provided on the light source light incident side of the circularly polarized light separating layer. . Diffusion layer is, for example, a method of forming a particle-dispersed resin layer, a method by surface roughening treatment such as sandblasting or chemical etching, a crazing generation method by mechanical stress or solvent treatment, a transfer formation by a mold provided with a predetermined diffusion structure It can be suitably formed as a coating layer or a diffusion sheet on the circularly polarized light separating layer by any method such as a method.
[0042]
Also, the diffusion layer should be placed for the purpose of leveling the light emitted from the optical element to suppress uneven brightness, and preventing glare due to moire due to interference with the pixels when applied to a liquid crystal cell. You can also. In this case, the circularly polarized light separating layer, the quarter wave plate, the polarized light, such as the side of the circularly polarized light separating layer provided with the quarter wave plate, the quarter wave plate or polarizing plate provided on the side, or the upper surface of the polarizing plate. One layer or two or more layers can be arranged at an appropriate position adjacent to a plate or the like. A diffusing layer that can be preferably used from the standpoint of maintaining the polarization state of the light emitted from the circularly polarized light separating layer is 30 nm or less based on perpendicular incident light having a wavelength difference of 633 nm, preferably incident light having an incident angle of 30 degrees or less. In particular, those of 0 to 20 nm.
[0043]
The quarter wave plate functions as a linearly polarized light converting means, and circularly polarized light emitted from the circularly polarized light separating layer is incident on the quarter wave plate and undergoes a phase change, and the phase change is a quarter wavelength. Is converted into linearly polarized light, and other wavelength light is converted into elliptically polarized light. The converted elliptically polarized light becomes flattened elliptically polarized light as it is closer to the wavelength of the light converted into the linearly polarized light. As a result, light in a state containing a large amount of linearly polarized light components that can pass through the polarizing plate is emitted from the quarter-wave plate.
[0044]
Accordingly, as shown in the figure, the quarter wavelength plate 3 is disposed on the light exit side of the circularly polarized light separating layer 1. When the cholesteric liquid crystal layer is superposed in the order of the center wavelength of the reflected light except for one base layer, the longer wavelength cholesteric liquid crystal layer side is set to the light emitting side in view of the suppression of the wavelength shift described above. It is preferable that As described above, the light can be easily transmitted through the polarizing plate by being converted to a state having a large amount of linearly polarized light components through the quarter-wave plate. For example, in the case of a liquid crystal display device, this polarizing plate is an optical layer that maintains a display quality by preventing a decrease in polarization characteristics caused by a change in viewing angle with respect to a liquid crystal cell, and realizes a higher degree of polarization. It functions as an optical layer that achieves good display quality.
[0045]
In other words, in the above, it is possible to achieve display by allowing the outgoing polarized light from the circularly polarized light separating layer to enter the liquid crystal cell as it is without using the polarizing plate, but the display quality is improved by using the polarizing plate. For example, a polarizing plate is used as necessary. In that case, the higher the transmittance with respect to the polarizing plate, the more advantageous from the point of display brightness, and the higher the transmittance, the higher the linearly polarized component in the polarization direction that coincides with the polarizing axis (transmission axis) of the polarizing plate. Therefore, for this purpose, the outgoing polarized light from the circularly polarized light separating layer is converted into predetermined linearly polarized light through the linearly polarized light converting means.
[0046]
As the quarter wave plate, the circularly polarized light emitted from the circularly polarized light separating layer can form a large amount of linearly polarized light corresponding to the phase difference of the quarter wavelength, and light of other wavelengths can be used as the linearly polarized light. Those having a major axis direction in a parallel direction as much as possible and capable of being converted into flat elliptical polarization as close as possible to linearly polarized light are preferable. By using such a quarter-wave plate, the linearly polarized direction of the emitted light and the major axis direction of the elliptically polarized light can be arranged so as to be as parallel as possible with the transmission axis of the polarizing plate, and can pass through the polarizing plate. Light with a large amount of linearly polarized light components can be obtained.
[0047]
The quarter-wave plate can be formed as a superimposed layer of one or more retardation plates. In the case of a quarter-wave plate composed of a single-layer retardation plate, the smaller the birefringence wavelength dispersion, the more preferable it is to make the polarization state uniform for each wavelength. On the other hand, the superposition of the phase difference plate is effective in improving the wavelength characteristics in the wavelength region, and the combination may be appropriately determined according to the wavelength region.
[0048]
Incidentally, as a single-layer type ¼ wavelength plate that can be preferably used for light in the visible light range from the viewpoint of wavelength range, conversion efficiency, etc., those having a small phase difference, especially 100 to 180 nm, particularly 110 to 150 nm or less. The phase difference is given. In addition, in the case of a quarter wavelength plate composed of two or more retardation plates, a layer that provides a phase difference of 100 to 180 nm is included in one or more odd layers, and a layer that provides a phase difference of 200 nm or more. A combination is preferable from the viewpoint of wavelength characteristics and the like.
[0049]
The retardation plate that forms the quarter-wave plate is preferably one that can be formed of an appropriate material and that provides a transparent and uniform retardation. In general, for example, a birefringent film formed by stretching a film made of an appropriate plastic such as polycarbonate, polysulfone, polyester, polymethyl methacrylate, polyamide, or polyvinyl alcohol is used.
[0050]
As illustrated in FIG. 4, a polarizing plate 4 can be provided on the quarter-wave plate 3 as necessary. Such an optical element can use the polarizing plate as a polarizing plate on the light source side of the liquid crystal cell. Further, the polarizing plate may be disposed in the circularly polarized light separating layer without using a quarter wavelength plate, and in this case, the circularly polarized light transmitted through the circularly polarized light separating layer is directly linearly polarized through the polarizing plate.
[0051]
As the polarizing plate, a suitable one can be used, but generally a polarizing film is used. Examples of polarizing films were stretched by adsorbing dichroic dyes such as iodine on hydrophilic polymer films such as polyvinyl alcohols, partially formalized polyvinyl alcohols, and partially saponified ethylene / vinyl acetate copolymers. And polyene oriented films such as polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products.
[0052]
As the polarizing plate attached to the circularly polarized light separating layer, a type containing a dichroic dye is particularly preferably used in view of the degree of polarization and the like. The thickness of the polarizing film is usually 5 to 80 μm, but is not limited thereto. The polarizing plate to be used may be one in which one or both sides of a polarizing film are covered with a transparent protective layer or the like.
[0053]
The circularly polarized light separating layer and the optical element according to the present invention can be preferably used for forming a polarized light source device. The polarized light source device can be formed by arranging a circularly polarized light separating layer or an optical element on the light source. In the case of the optical element having the diffusion layer 2 on the outer surface as shown in FIG. 2, the light source is disposed on the diffusion layer side, and the circularly polarized light separation layer has the quarter wavelength plate 3 and the like as shown in FIGS. In some cases, the light source is arranged on the side not having the quarter wavelength plate or the like.
[0054]
FIG. 5 shows an example of the polarized light source device 5. This shows a case where a circularly polarized light separating layer is used as an optical element, 51 is a light guide plate, and 52 is a light source. The light guide plate 51 is a light source that emits incident light from the light source 52 disposed on the side surface from the upper surface (circular polarization separation layer side), functions integrally with the light source 52, and supplies light to the circular polarization separation layer. It functions.
[0055]
According to the polarized light source device 5, the incident light from the light source 52 is emitted from the upper surface of the light guide plate 51, and the light in the vertical direction is incident on the circularly polarized light separating layer 1 disposed on the emission surface side and left and right ones. Circularly polarized light is transmitted and the other circularly polarized light is reflected and reenters the light guide plate 51 as return light. The light re-entering the light guide plate is reflected by the reflective layer 54 on the lower surface and again enters the circularly polarized light separating layer 1 to be separated again into transmitted light and reflected light (re-incident light).
[0056]
On the other hand, the return light obliquely incident on the circularly polarized light separating layer 1 and totally reflected by the base layer described above is also incident on the reflective layer 54 on the lower surface of the light guide plate and reflected, and again passes through the diffusing layer 2 to return to the circularly polarized light separating layer. 1 is incident. In this case, a part of the re-incident light is converted into light that can be perpendicularly incident on the circularly polarized light separating layer by diffusion through the diffusion layer 2, and behaves in the same manner as the light in the vertical direction described above. The remaining light behaves again as obliquely incident light. Accordingly, the front luminance can be improved as the ratio of the return light of obliquely incident light that is converted into light that can be vertically incident on the circularly polarized light separating layer by diffusion is larger.
[0057]
As described above, the light source in the polarized light source device is preferably a light guide plate type that emits incident light from the light source disposed on the side surface from one of the upper and lower surfaces from the viewpoint of improving the light utilization efficiency. As the light guide plate, an appropriate one can be used, but in general, one made of a plate-like material having an upper and lower surfaces, one of which is an emission surface, and an incident surface consisting of at least one side surface between the upper and lower surfaces is used. .
[0058]
The shape of the light guide plate is excellent in the output efficiency from the output surface, the output light is excellent in the perpendicularity to the output surface and easy to use effectively, and the output efficiency of the re-incident light through the circularly polarized light separation layer is also excellent. From the standpoint of the proximity of the emission direction to the initial emission direction, a structure having fine prism-like irregularities, in particular, a convex part or a concave part composed of a long side surface and a short side surface is preferable (Japanese Patent Application No. 7). -321036). Further, it is preferable that the thickness of the side end portion facing the incident surface is thinner than that of the incident surface, especially 50% or less.
[0059]
The thickness of the opposite end with respect to the incident surface is such that light incident from the incident surface is efficiently incident on the short side surface of the prism-shaped uneven surface before reaching the opposite end as the transmission end. This is advantageous in that incident light can be efficiently supplied to the target surface after being output from the output surface via reflection. Further, such a thinned structure can reduce the weight of the light guide plate. For example, when the prism-shaped uneven surface is linear, the weight can be about 75% of the uniform thickness of the light guide plate.
[0060]
The pitch of the convex portions or concave portions on the prism-shaped uneven surface is preferably smaller than the points such as suppression of unevenness of light and darkness and prevention of moire with the liquid crystal cell because emitted light is usually emitted in a stripe shape through the convex portions or concave portions. . A preferable period of the convex portion or the concave portion in consideration of the manufacturing accuracy is 500 μm or less, especially 300 μm or less, particularly 5 to 200 μm.
[0061]
The light guide plate can be formed of an appropriate material exhibiting transparency according to the wavelength region of the light source. By the way, in the visible light region, for example, an acrylic resin such as polymethyl methacrylate, a polycarbonate resin such as polycarbonate or a polycarbonate / polystyrene copolymer, a transparent resin typified by an epoxy resin or the like, a glass of about 400 to 700 nm. The thing which shows transparency in a wavelength range is mention | raise | lifted.
[0062]
The light guide plate may be formed by an appropriate method. As a preferable production method from the viewpoint of mass productivity, for example, a liquid resin that can be polymerized by heat, ultraviolet rays, radiation, or the like is filled or cast into a mold that can form predetermined prismatic unevenness, and a polymerization treatment is performed. , A method of transferring a shape by pressing a thermoplastic resin to a mold capable of forming predetermined prismatic irregularities under heating, a heat-melted thermoplastic resin or a resin fluidized through heat or a solvent A method such as injection molding that fills a mold that can be molded into a shape can be used.
[0063]
The light guide plate may be formed as a laminate of dissimilar materials, such as a light guide portion that carries light transmission and a prism-shaped uneven surface forming sheet adhered thereto. It does not have to be formed as a layered product. In the above-described light guide plate, the characteristics such as the angular distribution and in-plane distribution of the emitted light are adjusted based on the control of the area ratio and inclination angle of the short side surface to the long side surface, the shape and curvature of the prismatic uneven surface, etc. Can do.
[0064]
The thickness of the light guide plate can be appropriately determined depending on the size of the light guide plate and the size of the light source depending on the purpose of use. The general thickness of the light guide plate when used in a liquid crystal display device or the like is 20 mm or less, especially 0.1 to 10 mm, particularly 0.5 to 8 mm, based on the incident surface.
[0065]
The reflective layer 54 disposed on the opposite surface of the light guide plate can be appropriately formed by a plated layer, a metal vapor-deposited layer, a metal foil, a metal vapor-deposited sheet, a plated sheet, or the like, and is integrated with the opposite surface of the light guide plate. Alternatively, they may be superimposed as a reflection sheet or the like, and an appropriate arrangement form can be adopted in the present invention. A metal reflecting surface is preferred from the point of reversing circularly polarized light through reflection.
[0066]
In addition, when a light diffusing type reflective layer is formed on the surface of the reflective layer by, for example, providing a fine concavo-convex structure, diffusion for diffusing the return light totally reflected through the base layer of the circularly polarized light separating layer It can also be set as the polarized light source device of the form which omitted the layer. In this case, the light diffusion type reflection layer can also serve as a course change due to diffusion of the return light.
[0067]
The light source of the light guide plate type is typically formed by arranging the light source 52 on the incident surface of the light guide plate 51 as illustrated in FIG. As the light source, an appropriate one can be used. For example, a linear light source such as a (cold, hot) cathode tube, a point light source such as a light emitting diode, or an array body such as a linear or planar shape can be preferably used. When forming the backlight, as shown in the figure, a light source holder 53 that surrounds the light source to guide the divergent light from the linear light source to the side surface of the light guide plate, or a prism for controlling the light emission direction, as shown in the figure. It can also be set as the combination body which arrange | positioned appropriate auxiliary means, such as a sheet | seat.
[0068]
A light guide plate that can be preferably used for forming a polarized light source device emits incident light from the side surface from the exit surface with high efficiency, and the emitted light has high directivity, and in particular, excellent directivity with respect to the exit surface. In addition, the re-emission efficiency of the re-incident light through the circularly polarized light separation layer is excellent, the directivity and the emission angle of the re-emission light match the directivity and the emission angle of the initial emission light as much as possible, and the circularly polarized light. In this case, the re-incident light through the separation layer is emitted with a small number of reflection repetitions, especially without repeated reflections.
[0069]
As described above, the polarized light source device according to the present invention prevents reflection loss and the like by reusing the reflected light (re-incident light) from the circularly polarized light separation layer as outgoing light by polarization conversion, and uses the outgoing light as needed. Converted into a light state containing a linearly polarized component richly through a quarter-wave plate, etc. to facilitate transmission through the polarizing plate, prevent absorption loss, and return totally reflected through the base layer of the circularly polarized light separating layer A part of the light is rerouted by diffusion and is emitted again from the circularly polarized light separation layer to improve the light utilization efficiency, particularly the front luminance.
[0070]
Therefore, the polarized light source device according to the present invention provides a light that is excellent in light utilization efficiency, bright as described above, excellent in the perpendicularity of emitted light, and has little unevenness in brightness and darkness. It can be preferably used in various devices as a backlight system in the device.
[0071]
FIG. 6 illustrates a liquid crystal display device 6 using the polarized light source device 5 according to the present invention in a backlight system. 61 is a liquid crystal cell, 62 is an upper polarizing plate, and 63 is a diffusion plate. The lower polarizing plate 4 and the diffusion plate 63 are provided as necessary. In general, a liquid crystal display device is formed by appropriately assembling components such as a liquid crystal cell functioning as a liquid crystal shutter and an accompanying driving device, a polarizing plate, a backlight, and a retardation plate if necessary. The In the present invention, there is no particular limitation except that the above-described polarized light source device is used, and it can be formed according to the conventional method. In particular, a direct-view liquid crystal display device can be preferably formed.
[0072]
Accordingly, the liquid crystal cell to be used is not particularly limited, and an appropriate one can be used. In particular, it is advantageously used for display by making polarized light incident on a liquid crystal cell. For example, it can be preferably used for a liquid crystal cell using a twisted nematic liquid crystal or a super twisted nematic liquid crystal, but a non-twisted liquid crystal. Or a guest-host type liquid crystal in which a dichroic dye is dispersed in a liquid crystal, or a liquid crystal cell using a ferroelectric liquid crystal. There is no particular limitation on the driving method of the liquid crystal.
[0073]
From the point of obtaining a good contrast ratio display due to the incidence of highly linearly polarized light, as a polarizing plate on the backlight side, particularly as a polarizing plate of iodine type or dye type as described above, for example, as described above. A liquid crystal display device using a high degree of polarization is preferable. When forming a liquid crystal display device, for example, a diffusion plate or antiglare layer provided on the polarizing plate on the viewing side, an antireflection film, a protective layer or protective plate, or a compensation retardation plate provided between the liquid crystal cell and the polarizing plate, as appropriate. An appropriate optical layer can be appropriately disposed.
[0074]
The compensation retardation plate is intended to improve visibility by compensating for the wavelength dependence of birefringence. In this invention, it arrange | positions as needed between the polarizing plate and liquid crystal cell of a visual recognition side or / and a backlight side. As the compensation phase difference plate, an appropriate one can be used according to the wavelength region and the like, and it may be formed as one layer or two or more overlapping layers. The compensation retardation plate can be obtained as an example of a stretched film as the above-described retardation plate for linear polarization conversion.
[0075]
In the present invention, the optical elements or parts forming the above-described polarized light source device or liquid crystal display device may be wholly or partially laminated and fixed, or arranged in an easily separated state. There may be.
[0076]
【Example】
Reference example
Four kinds of acrylic main chain side-chain cholesteric liquid crystal polymers with different glass transition temperatures are formed on a polyimide rubbing-treated surface of a 30 μm thick triacetyl cellulose film by spin coating (thickness: 2 μm), and then at a predetermined temperature. And then rapidly cooled to obtain four kinds of cholesteric liquid crystal layers exhibiting a mirror-like selective reflection state, transmitting left circularly polarized light, and having a central wavelength of selective reflection of 470 nm, 550 nm, 640 nm, or 770 nm.
[0077]
Example 1
A cholesteric liquid crystal layer with selective reflection center wavelengths of 470 nm and 550 nm is disposed between the base layer made of a cholesteric liquid crystal layer with a selective reflection center wavelength of 640 nm obtained in the reference example, and a circularly polarized light separating plate is formed. Obtained.
[0078]
Next, a quarter wavelength plate having a front phase difference of 140 nm is bonded to the side near the cholesteric liquid crystal layer having a central wavelength of selective reflection of 550 nm in the circularly polarized light separating plate, and on the quarter wavelength plate. A polarizing plate was adhered with the transmission axis aligned with the linear polarization plane to obtain an optical element.
[0079]
Example 2
According to Example 1, a circularly polarized light separating plate was obtained by sequentially laminating six cholesteric liquid crystal layers with selective reflection center wavelengths of 470 nm, 550 nm, 640 nm, 470 nm, 550 nm, and 640 nm in this order. An element was obtained.
[0080]
Example 3
According to Example 1, a circularly polarized light separating plate was obtained by sequentially laminating seven cholesteric liquid crystal layers with selective reflection center wavelengths of 470 nm, 550 nm, 640 nm, 770 nm, 470 nm, 550 nm, and 640 nm in this order. Thus, an optical element was obtained.
[0081]
Comparative Example 1
In accordance with Example 1, a circularly polarized light separation plate was obtained by sequentially laminating three cholesteric liquid crystal layers having selective reflection center wavelengths of 470 nm, 550 nm, and 640 nm in this order, and an optical element was obtained using the same.
[0082]
Comparative Example 2
According to Example 1, a circularly polarized light separation plate was obtained by sequentially laminating four cholesteric liquid crystal layers with selective reflection center wavelengths of 470 nm, 550 nm, 640 nm, and 770 nm in this order, and an optical element was obtained using the same. .
[0083]
Evaluation test
A cold cathode tube with a diameter of 3 mm is arranged on the side of the light guide plate having a fine prism structure formed on the lower surface, the cold cathode tube is surrounded by a light source holder made of a silver deposited polyester film, and the silver deposited polyester is formed on the lower surface of the light guide plate. A diffusion sheet containing silica particles and having a fine concavo-convex structure is arranged on the upper surface of a sidelight type surface light source device in which a reflection sheet made of a film is arranged, and obtained in Examples and Comparative Examples thereon. The optical element was placed with the polarizing plate facing upward to obtain a polarized light source device.
[0084]
Next, a commercially available TFT type liquid crystal panel is arranged on the upper surface of the polarizing plate in the polarized light source device to obtain a liquid crystal display device, and the backlight is turned on using a luminance meter (BM-5 manufactured by Topcon Corporation). The front brightness in the vertical direction of the panel was examined. The results are shown in the following table.
[0085]

[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an example of a circularly polarized light separating layer
FIG. 2 is a cross-sectional view of an optical element example
FIG. 3 is a sectional view of another optical element example.
FIG. 4 is a cross-sectional view of still another optical element example.
FIG. 5 is a sectional view of an example of a polarized light source device.
FIG. 6 is a cross-sectional view of an example of a liquid crystal display device
[Explanation of symbols]
1: Circularly polarized light separating layer
11, 13: Base layer comprising a cholesteric liquid crystal layer
12, 14: Medium for changing the polarization state
15 and 16: External arrangement layers composed of cholesteric liquid crystal layers
2: Diffusion layer
3: 1/4 wavelength plate
4: Polarizing plate
5: Polarized light source device
51: Light guide plate
52: Light source
54: Reflective layer
6: Liquid crystal display device

Claims (9)

  A circularly polarized light separating layer, characterized in that a medium for changing the polarization state is disposed between a base layer made of a cholesteric liquid crystal layer whose difference in center wavelength of reflected light is within 20 nm.   2. The medium according to claim 1, wherein the medium for changing the polarization state comprises one or more cholesteric liquid crystal layers, and the central wavelength of the reflected light of the cholesteric liquid crystal layer differs from that of at least one base layer by 80 nm or more. A circularly polarized light separating layer.   3. The circularly polarized light separating layer according to claim 1, wherein one or two or more cholesteric liquid crystal layers having a central wavelength of reflected light different from that of the base layer by 80 nm or more are provided outside one or both of the base layers.   4. The circularly polarized light separating layer according to claim 2, wherein the cholesteric liquid crystal layer disposed between the base layers exhibits a half-wave plate function for obliquely transmitted light. An optical element comprising a diffusion layer on one of the circularly polarized light separating layers according to claim 1. An optical element comprising a quarter-wave plate on one of the circularly polarized light separating layers according to claim 1.   The optical element according to claim 6, further comprising a polarizing plate containing a dichroic dye on the upper side of the quarter-wave plate. Above the light source having a reflective layer, the polarization light source device characterized by having an optical element according to one of the circularly polarized light separation layer or claim 5 to 7 according to one of claims 1 to 4.   A liquid crystal display device comprising a liquid crystal cell above the circularly polarized light separating layer in the polarized light source device according to claim 8.

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