JP2004004764A - Light condensing system and transmission type liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light condensing system effectively shielding remaining transmission light in an oblique direction, suppressing unpleasant coloring, having satisfactory display, and also, having reduced cost. <P>SOLUTION: The light condensing system includes a back light system equipped with a light source and a primary light condensing part (X) capable of condensing the light emitted from the light source within the extent of ±60° in the front direction and a light condensing film having no pattern structure as a secondary light condensing element (Y). <P>COPYRIGHT: (C)2004,JPO

Description

で表される。数１中、Ｓ１：第一格子ピッチ、Ｓ２：第二格子ピッチ、Ｓ３：モアレ縞ピッチ、α：第一格子と第二格子のなす角度、である。
【００８２】
このように異なる格子を重ね合わせて得られるモアレ縞の強度Ｉの最大値をＩｍａｘ、最小値をＩｍｉｎとして、モアレ縞の可視度（Ｖ：ｖｉｓｉｂｉｌｉｔｙ）を計算すると、数式：Ｖ＝（Ｉｍａｘ−Ｉｍｉｎ）／（Ｉｍａｘ＋Ｉｍｉｎ）、で表される。このコントラストを低減するには格子同士が成す角度が十分に大きく、直交に近いことが望まれる。しかし、格子を有する層が３層以上では要件を満たすことが困難になる。従って、モアレ現象を抑制するには格子構造を有する層の削減が効果的であることが分かる。
【００８３】
（反射偏光子（ａ））
輝度向上の観点よりは視感度の高い５５０ｎｍ付近の波長の光に対して、その全反射が達成されることが望ましく、少なくとも５５０ｎｍ±１０ｎｍの波長領域で反射偏光子（ａ）の選択反射波長が重なっていることが望ましい。
【００８４】
例えば液晶表示装置に多く用いられているウエッジ型導光板を用いたバックライトでは導光板からの出射光の角度は法線方向から６０°前後の角度である。この角度でのブルーシフト量は約１００ｎｍにも及ぶ。従ってバックライトに３波長冷陰極管が用いられている場合には赤の輝線スペクトルが６１０ｎｍであるので選択反射波長は少なくとも７１０ｎｍより長波長側に達する必要があると分かる。この長波長側に必要な選択反射波長帯域幅は上記のように光源からの入射光線の角度と波長に大きく依存するので要求仕様に応じて任意に長波長端を設定する。
【００８５】
バックライト光源が特定の波長しか発光しない場合、例えば色付き冷陰極管のような場合には得られる輝線のみ遮蔽できればよい。
【００８６】
また、バックライトからの出射光線が動向体表面に加工されたマイクロレンズやドット、プリズムなどの設計で正面方向に最初からある程度絞られている場合には大きな入射角での透過光は無視できるので選択反射波長を大きく長波長側に延ばさなくても良い。組み合わせ部材・光源種に合わせて適宜設計できる。
【００８７】
かかる観点より反射偏光子（ａ）は全く同一の組合せでも良いし、一方が可視光全波長で反射を有するもので、他方が部分的に反射するものでも良い。
【００８８】
（円偏光型反射偏光子（ａ１））
円偏光型反射偏光子（ａ１）としては、たとえば、コレステリック液晶材料が用いられる。円偏光型反射偏光子（ａ１）においては選択反射の中心波長はλ＝ｎｐで決定される（ｎはコレステリック材料の屈折率、ｐはカイラルピッチ）。斜め入射光に対しては、選択反射波長がブルーシフトするため、前記重なっている波長領域はより広い方が好ましい。
【００８９】
円偏光型反射偏光子（ａ１）がコレステリック材料の場合、異なるタイプ（右ねじれと左ねじれ）の組み合わせでも同様の考え方で正面位相差がλ／２で傾けると位相差がゼロまたはλであれば同様の偏光子が得られるが、傾斜する軸の方位角による異方性や色付きの問題が発生するため好ましくない。かかる観点より同じタイプ同士の組み合わせ（右ねじれ同士、左ねじれ同士）が好ましいが、上下のコレステリック液晶分子、あるいはＣプレートの波長分散特性が異なる物の組み合わせで相殺することで色づきを押さえることもできる。
【００９０】
円偏光型反射偏光子（ａ１）を構成するコレステリック液晶には、適宜なものを用いてよく、特に限定はない。例えば、高温でコレステリック液晶性を示す液晶ポリマー、または液晶モノマーと必要に応じてのカイラル剤および配向助剤を電子線や紫外線などの電離放射線照射や熱により重合せしめた重合性液晶、またはそれらの混合物などがあげられる。液晶性はリオトロピックでもサーモトロピック性のどちらでもよいが、制御の簡便性およびモノドメインの形成しやすさの観点よりサーモトロピック性の液晶であることが望ましい。
【００９１】
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。例えば、トリアセチルセルロースやアモルファスポリオレフィンなどの複屈折位相差が可及的に小さな支持基材上に、ポリイミド、ポリビニルアルコール、ポリエステル、ポリアリレート、ポリアミドイミド、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、またはＳｉＯ_２　の斜方蒸着層、またはポリエチレンテレフタレートやポリエチレンナフタレートなどの延伸基材表面性状を配向膜として利用した基材、または上記基材表面をラビング布やベンガラに代表される微細な研磨剤で処理し、表面に微細な配向規制力を有する微細凹凸を形成した基材、または上記基材フィルム上にアゾベンゼン化合物など光照射により液晶規制力を発生する配向膜を形成した基材、等からなる適当な配向膜上に、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プラナー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。
【００９２】
また配向状態が形成された段階で紫外線やイオンビーム等のエネルギー照射で構造を固定してもよい。上記基材で複屈折が小さなものは液晶層支持体としてそのまま用いてもよい。複屈折が大きなもの、または偏光素子（Ａ）の厚みに対する要求が厳しい場合には配向基材より液晶層を剥離して適宜に用いることもできる。
【００９３】
液晶ポリマーの製膜は、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、ロールコート法、フローコート法、プリント法、ディップコート法、流延成膜法、バーコート法、グラビア印刷法等で薄層展開し、さらに、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、トリクロロエチレン、テトラクロロエタンのような塩素系溶媒；アセトン、メチルエチルケトン、シクロヘキサノンのようなケトン系溶媒；トルエンのような芳香族溶媒；シクロヘプタンのような環状アルカン；またはＮ−メチルピロリドンやテトラヒドロフラン等を適宜に用いることができる。
【００９４】
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を採用することができる。当該方法は、溶媒を使用しない方法であり、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。
【００９５】
さらに必要に応じ、これらの光学層を成膜時に用いる支持基材／配向基材から剥離し、他の光学材料に転写して用いることもできる。
【００９６】
（直線偏光型反射偏光子（ａ２））
直線偏光型反射偏光子（ａ２）としては、グリッド型偏光子、屈折率差を有する２種以上の材料による２層以上の多層薄膜積層体、ビームスプリッターなどに用いられる屈折率の異なる蒸着多層薄膜、複屈折を有する２種以上の材料による２層以上の複屈折層多層薄膜積層体、複屈折を有する２種以上の樹脂を用いた２層以上の樹脂積層体を延伸したもの、直線偏光を直交する軸方向で反射／透過することで分離するものなどがあげられる。
【００９７】
例えばポリエチレンナフタレート、ポリエチレンテレフタレート、ポリカーボネートに代表される延伸により位相差を発生する材料やポリメチルメタクリレートに代表されるアクリル系樹脂、ＪＳＲ社製のアートンに代表されるノルボルネン系樹脂等の位相差発現量の少ない樹脂を交互に多層積層体として一軸延伸して得られるものを用いることができる。
【００９８】
（位相差層（ｂ））
円偏光型反射偏光子（ａ１）または直線偏光型反射偏光子（ａ２）の間に配置する位相差層（ｂ１）は、正面方向の位相差が略ゼロであり、法線方向から３０°の角度の入射光に対してλ／８以上の位相差を有するものである。正面位相差は垂直入射された偏光が保持される目的であるので、λ／１０以下であることが望ましい。
【００９９】
斜め方向からの入射光に対しては効率的に偏光変換されるべく全反射させる角度などによって適宜決定される。例えば、法線からのなす角６０°程度で完全に全反射させるには６０°で測定したときの位相差がλ／２程度になるように決定すればよい。ただし、円偏光型反射偏光子（ａ１）による透過光は、円偏光型反射偏光子（ａ１）自身のＣプレート的な複屈折性によっても偏光状態が変化しているため、通常挿入されるＣプレートのその角度で測定したときの位相差はλ／２よりも小さな値でよい。Ｃプレートの位相差は入射光が傾くほど単調に増加するため、効果的な全反射を３０°以上のある角度傾斜した時に起こさせる目安として３０°の角度の入射光に対してλ／８以上有すればよい。
【０１００】
本発明の偏光素子（Ａ）にて正面より３０°の入射角を有する光線に対して有効な遮蔽を行い得る設計の場合、実質的には入射角２０°前後の領域で十分に透過光線が低下している。この領域の光線に限定される場合、一般的なＴＮ液晶表示装置の良好な表示を示す領域の光線のみが透過する。用いるＴＮ液晶表示装置のセル内液晶種や配向状態、プレティルト角などの条件により変動があるが階調反転やコントラストの急激な劣化は生じないため、本発明における視野角拡大のためには用いられる水準となる。より正面光のみに絞り込むために位相差層の位相差値をより大きく取ったり、ＴＮ液晶に補償位相差板を組み合わせることを前提に位相差値を小さくして絞り込みを穏やかにして用いても良い。
【０１０１】
位相差層（ｂ１）の材質は上記のような光学特性を有するものであれば、特に制限はない。例えば、可視光領域（３８０ｎｍ〜７８０ｎｍ）　以外に選択反射波長を有するコレステリック液晶のプラナー配向状態を固定したものや、棒状液晶のホメオトロピック配向状態を固定したもの、ディスコチック液晶のカラムナー配向やネマチック配向を利用したもの、負の１軸性結晶を面内に配向させたもの、２軸性配向したポリマーフィルムなどがあげられる。
【０１０２】
Ｃプレートとしては、たとえば、可視光領域（３８０ｎｍ〜７８０ｎｍ）以外に選択反射波長を有するコレステリック液晶のプラナー配向状態を固定したＣプレートは、コレステリック液晶の選択反射波長としては、可視光領域に色付きなどがないことが望ましい。そのため、選択反射光が可視領域にない必要がある。選択反射はコレステリックのカイラルピッチと液晶の屈折率によって一義的に決定される。選択反射の中心波長の値は近赤外領域にあっても良いが、旋光の影響などを受けるため、やや複雑な現象が発生するため、３５０ｎｍ以下の紫外部にあることがより望ましい。コレステリック液晶層の形成については、前記した反射偏光子におけるコレステリック層形成と同様に行われる。
【０１０３】
ホメオトロピック配向状態を固定したＣプレートは、高温でネマチック液晶性を示す液晶性熱可塑樹脂または液晶モノマーと必要に応じての配向助剤を電子線や紫外線などの電離放射線照射や熱により重合せしめた重合性液晶、またはそれらの混合物が用いられる。液晶性はリオトロピックでもサーモトロピック性のいずれでもよいが、制御の簡便性やモノドメインの形成しやすさの観点より、サーモトロピック性の液晶であることが望ましい。ホメオトロピック配向は、例えば、垂直配向膜（長鎖アルキルシランなど）を形成した膜上に前記複屈折材料を塗設し、液晶状態を発現させ固定することによって得られる。
【０１０４】
ディスコティック液晶を用いたＣプレートとしては、液晶材料として面内に分子の広がりを有したフタロシアニン類やトリフェニレン類化合物のごとく負の１軸性を有するディスコティック液晶材料を、ネマチック相やカラムナー相を発現させて固定したものである。負の１軸性無機層状化合物としては、たとえば、特開平６−８２７７７号公報などに詳しい。
【０１０５】
ポリマーフィルムの２軸性配向を利用したＣプレートは、正の屈折率異方性を有する高分子フィルムをバランス良く２軸延伸する方法、熱可塑樹脂をプレスする方法、平行配向した結晶体から切り出す方法などにより得られる。
【０１０６】
直線偏光型反射偏光子（ａ２）を用いる場合には、位相差層（ｂ１）として、正面方向の位相差が略ゼロであり、法線方向から３０°の角度の入射光に対してλ／４以上の位相差を有するものが用いられる。前記位相差層（ｂ１）の両側に、正面位相差が略λ／４であるλ／４板（ｂ２）を用いて直線偏光を一度円偏光に変換した後に前述の円偏光板と同様な方法で平行光化することができる。この場合の構成断面と各層の配置は図３、図４、図５に示した通りである。この場合、λ／４板（ｂ２）の遅相軸と直線偏光型反射偏光子（ａ２）の偏光軸の成す角度は前述の通りであり、λ／４板（ｂ２）同士の軸角度は任意に設定できる。
【０１０７】
前記位相差層（ｂ２）としては、具体的には、λ／４板が用いられる。λ／４板は、使用目的に応じた適宜な位相差板が用いられる。λ／４板は、２種以上の位相差板を積層して位相差等の光学特性を制御することができる。位相差板としては、ポリカーボネート、ノルボルネン系樹脂、ポリビニルアルコール、ポリスチレン、ポリメチルメタクリレート、ポリプロピレンやその他のポリオレフィン、ポリアリレート、ポリアミドの如き適宜なポリマーからなるフィルムを延伸処理してなる複屈折性フィルムや液晶ポリマーなどの液晶材料からなる配向フィルム、液晶材料の配向層をフィルムにて支持したものなどがあげられる。
【０１０８】
可視光域等の広い波長範囲でλ／４板として機能する位相差板は、例えば波長５５０ｎｍの淡色光に対してλ／４板として機能する位相差層と他の位相差特性を示す位相差層、例えば１／２波長板として機能する位相差層とを重畳する方式などにより得ることができる。従って、偏光板と輝度向上フィルムの間に配置する位相差板は、１層又は２層以上の位相差層からなるものであってよい。
【０１０９】
また、正面位相差が略λ／４であり、厚み方向位相差がλ／２以上であるような２軸性位相差層（ｂ３）を２枚配置することでも同様な効果を得ることができる。２軸性位相差層（ｂ３）は、Ｎｚ係数が略２以上であれば上記要件を満たす。この場合の構成断面と各層の配置は図６、図７に示した通りである。この場合、２軸性位相差層（ｂ３）との遅相軸と直線偏光型反射偏光子（ａ２）の偏光軸は前述の通りであり、２軸性位相差層（ｂ３）同士の軸角度は任意に設定できる。
【０１１０】
なお、正面位相差が略λ／４であることは、５５０ｎｍ波長の光に対してλ／４±４０ｎｍ程度、さらには±１５ｎｍの範囲に入るものであることが好ましい。
【０１１１】
また、正面位相差が略λ／２であり、厚み方向位相差がλ／２以上であるような２軸性位相差層（ｂ４）を１枚用いることでも同様な効果を得ることができる。２軸性位相差層（ｂ４）は、Ｎｚ係数が略１．　５以上であれば上記要件を満たす。この場合の構成断面と各層の配置は図８、図９に示した通りである。この場合、上下の直線偏光型反射偏光子（ａ２）と中央の２軸性位相差層（ｂ４）の軸角度の関係は指定したとおりの角度となり一義的に決定される。
【０１１２】
なお、正面位相差が略λ／２であることは、５５０ｎｍ波長の光に対してλ／２±４０ｎｍ程度、さらには±１５ｎｍの範囲に入るものが好ましい。
【０１１３】
具体的に前記２軸性位相差層（ｂ３）、（ｂ４）としては、ポリカーボネートやポリエチレンテレフタレート等の複屈折性を有するプラスチック材料を２軸延伸したもの、または液晶材料を平面方向では一軸配向させ、厚み方向にさらに配向させたハイブリッド配向したものが用いられる。液晶材料を１軸性にホメオトロピック配向させたものも可能であり、前記コレステリック液晶を製膜した方法と同様に行われる。ただし、コレステリック液晶ではなくネマチック液晶材料を用いる必要がある。
【０１１４】
（拡散反射板の配置）
光源たる導光板の下側（液晶セルの配置面とは反対側）には拡散反射板の配置が望ましい。平行光化フィルムにて反射される光線の主成分は斜め入射成分であり、平行光化フィルムにて正反射されてバックライト方向へ戻される。ここで背面側の反射板が正反射性が高い場合には反射角度が保存され、正面方向に出射できずに損失光となる。従って反射戻り光線の反射角度を保存せず、正面方向へ散乱反射成分を増大させるため拡散反射板の配置が望ましい。
【０１１５】
（拡散板の配置）
平行光化フィルムとバックライト光源の間には適当な拡散板を設置することも望ましい。斜め入射し、反射された光線をバックライト導光体近傍にて散乱させ、その一部を垂直入射方向へ散乱せしめることで光の再利用効率が高まるためである。
【０１１６】
用いられる拡散板は表面凹凸形状による物の他、屈折率が異なる微粒子を樹脂中に包埋する等の方法で得られる。この拡散板は平行光化フィルムとバックライト間に挟み込んでも良いし、平行光化フィルムに貼り合わせてもよい。
【０１１７】
平行光化フィルムを貼り合わせた液晶セルをバックライトと近接して配置する場合、フィルム表面とバックライトの隙間でニュートンリングが生じる恐れがあるが、本発明における平行光化フィルムの導光板側表面に表面凹凸を有する拡散板を配置することによってニュートンリングの発生を抑制することができる。また、本発明における平行光化フィルムの表面そのものに凹凸構造と光拡散構造を兼ねた層を形成しても良い。
【０１１８】
（視野角拡大層の配置）
本発明の液晶表示装置における視野角拡大は、平行光化されたバックライトと組み合わされた、液晶表示装置から得られる正面近傍の良好な表示特性の光線を拡散し、全視野角内で均一で良好な表示特性を得ることによって得られる。
【０１１９】
ここで用いられる視野角拡大層は実質的に後方散乱を有さない拡散板が用いられる。拡散板は、拡散粘着材により設けることができる。配置場所は液晶表示装置の視認側であるが偏光板の上下いずれでも使用可能である。ただし画素のにじみ等の影響やわずかに残る後方散乱によるコントラスト低下を防止するために偏光板〜液晶セル間など、可能な限りセルに近い層に設けることが望ましい。またこの場合には実質的に偏光を解消しないフィルムが望ましい。例えば特開２０００−３４７００６号公報、特開２０００−３４７００７号公報に開示されているような微粒子分散型拡散板が好適に用いられる。
【０１２０】
液晶セルの視認側の偏光板より外側に視野角拡大層を位置する場合には液晶セル−偏光板まで平行光化された光線が透過するので、ＴＮ液晶セルの場合は特に視野角補償位相差板を用いなくともよい。ＳＴＮ液晶セルの場合には正面特性のみ良好に補償した位相差フィルムを用いるだけでよい。この場合には視野角拡大層が空気表面を有するので表面形状による屈折効果によるタイプの採用も可能である。
【０１２１】
一方で、偏光板と液晶セルの間に視野角拡大層を挿入する場合には偏光板を透過する段階では拡散光線となっている。ＴＮ液晶の場合、偏光子そのものの視野角特性は補償する必要がある。この場合には偏光板の視野角特性を補償する位相差板を偏光板と視野角拡大層の間に挿入するのが好ましい。ＳＴＮ液晶の場合にはＳＴＮ液晶の正面位相差補償に加えて偏光板の視野角特性を補償する位相差板を挿入するのが好ましい。
【０１２２】
従来から存在するマイクロレンズアレイフィルムやホログラムフィルムのように、内部に規則性構造体を有する視野角拡大フィルムの場合、液晶表示装置のブラックマトリクスや従来のバックライトの平行光化システムが有するマイクロレンズアレイ／プリズムアレイ／ルーバー／マイクロミラーアレイ等の微細構造と干渉しモアレを生じやすかった。しかし本発明における平行光化フィルムは面内に規則性構造が視認されず、出射光線に規則性変調が無いので視野角拡大層との相性や配置順序を考慮する必要はない。従って、視野角拡大層は液晶表示装置の画素ブラックマトリクスと干渉／モアレを発生しなければ特に制限はなく選択肢は広い。
【０１２３】
本発明においては視野角拡大層として実質的に後方散乱を有さない、偏光を解消しない、特開２０００−３４７００６号公報、特開２０００−３４７００７号公報に記載されているような光散乱板で、ヘイズ８０％〜９０％のものが好適に用いられる。その他、ホログラムシート、マイクロプリズムアレイ、マイクロレンズアレイ等、内部に規則性構造を有していても液晶表示装置の画素ブラックマトリクスと干渉／モアレを形成しなければ使用可能である。
【０１２４】
（各層の積層）
前記各層の積層は、重ね置いただけでも良いが、作業性や、光の利用効率の観点より各層を接着剤や粘着剤を用いて積層することが望ましい。その場合、接着剤または粘着剤は透明で、可視光域に吸収を有さず、屈折率は、各層の屈折率と可及的に近いことが表面反射の抑制の観点より望ましい。かかる観点より、例えば、アクリル系粘着剤などが好ましく用いうる。各層は、それぞれ別途配向膜状などでモノドメインを形成し、透光性基材へ転写などの方法によって順次積層していく方法や、接着層などを設けず、配向のために、配向膜などを適宜形成し、各層を順次直接形成して行くことも可能である。
【０１２５】
各層および（粘）接着層には、必要に応じて拡散度合い調整用に更に粒子を添加して等方的な散乱性を付与することや、紫外線吸収剤、酸化防止剤、製膜時のレベリング性付与の目的で界面活性剤などを適宜に添加することができる。
【０１２６】
（その他の材料）
なお、液晶表示装置には、常法に従って、各種の光学層等が適宜に用いられて作製される。
【０１２７】
偏光板（ＰＬ）は、液晶セルの両側に配置される。液晶セルの両側に配置された偏光板（ＰＬ）は、偏光軸が互いに略直交するように配置される。また入射側の偏光板（ＰＬ）はその偏光軸方向と、光源側からの透過で得られる直線偏光の軸方向とが揃うように配置される。
【０１２８】
偏光板は、通常、偏光子の片側または両側に保護フィルムを有するものが一般に用いられる。
【０１２９】
偏光子は、特に制限されず、各種のものを使用できる。偏光子としては、たとえば、ポリビニルアルコール系フィルム、部分ホルマール化ポリビニルアルコール系フィルム、エチレン・酢酸ビニル共重合体系部分ケン化フィルム等の親水性高分子フィルムに、ヨウ素や二色性染料等の二色性物質を吸着させて一軸延伸したもの、ポリビニルアルコールの脱水処理物やポリ塩化ビニルの脱塩酸処理物等ポリエン系配向フィルム等があげられる。これらのなかでもポリビニルアルコール系フィルムとヨウ素などの二色性物質からなる偏光子が好適である。これら偏光子の厚さは特に制限されないが、一般的に、５〜８０μｍ程度である。
【０１３０】
ポリビニルアルコール系フィルムをヨウ素で染色し一軸延伸した偏光子は、たとえば、ポリビニルアルコールをヨウ素の水溶液に浸漬することによって染色し、元長の３〜７倍に延伸することで作製することができる。必要に応じてホウ酸や硫酸亜鉛、塩化亜鉛等を含んでいてもよいヨウ化カリウムなどの水溶液に浸漬することもできる。さらに必要に応じて染色の前にポリビニルアルコール系フィルムを水に浸漬して水洗してもよい。ポリビニルアルコール系フィルムを水洗することでポリビニルアルコール系フィルム表面の汚れやブロッキング防止剤を洗浄することができるほかに、ポリビニルアルコール系フィルムを膨潤させることで染色のムラなどの不均一を防止する効果もある。延伸はヨウ素で染色した後に行っても良いし、染色しながら延伸してもよいし、また延伸してからヨウ素で染色してもよい。ホウ酸やヨウ化カリウムなどの水溶液中や水浴中でも延伸することができる。
【０１３１】
前記偏光子の片面または両面に設けられる透明保護フィルムを形成する材料としては、透明性、機械的強度、熱安定性、水分遮蔽性、等方性などに優れるものが好ましい。例えば、ポリエチレンテレフタレートやポリエチレンナフタレート等のポリエステル系ポリマー、ジアセチルセルロースやトリアセチルセルロース等のセルロース系ポリマー、ポリメチルメタクリレート等のアクリル系ポリマー、ポリスチレンやアクリロニトリル・スチレン共重合体（ＡＳ樹脂）等のスチレン系ポリマー、ポリカーボネート系ポリマーなどがあげられる。また、ポリエチレン、ポリプロピレン、シクロ系ないしはノルボルネン構造を有するポリオレフィン、エチレン・プロピレン共重合体の如きポリオレフィン系ポリマー、塩化ビニル系ポリマー、ナイロンや芳香族ポリアミド等のアミド系ポリマー、イミド系ポリマー、スルホン系ポリマー、ポリエーテルスルホン系ポリマー、ポリエーテルエーテルケトン系ポリマー、ポリフェニレンスルフィド系ポリマー、ビニルアルコール系ポリマー、塩化ビニリデン系ポリマー、ビニルブチラール系ポリマー、アリレート系ポリマー、ポリオキシメチレン系ポリマー、エポキシ系ポリマー、または前記ポリマーのブレンド物なども前記透明保護フィルムを形成するポリマーの例としてあげられる。透明保護フィルムは、アクリル系、ウレタン系、アクリルウレタン系、エポキシ系、シリコーン系等の熱硬化型、紫外線硬化型の樹脂の硬化層として形成することもできる。
【０１３２】
また、特開２００１−３４３５２９号公報（ＷＯ０１／３７００７）に記載のポリマーフィルム、たとえば、（Ａ）側鎖に置換および／または非置換イミド基を有する熱可塑性樹脂と、（Ｂ）側鎖に置換および／非置換フェニルならびにニトリル基を有する熱可塑性樹脂を含有する樹脂組成物があげられる。具体例としてはイソブチレンとＮ−メチルマレイミドからなる交互共重合体とアクリロニトリル・スチレン共重合体とを含有する樹脂組成物のフィルムがあげられる。フィルムは樹脂組成物の混合押出品などからなるフィルムを用いることができる。
【０１３３】
保護フィルムの厚さは、適宜に決定しうるが、一般には強度や取扱性等の作業性、薄層性などの点より１〜５００μｍ程度である。特に１〜３００μｍが好ましく、５〜２００μｍがより好ましい。
【０１３４】
また、保護フィルムは、できるだけ色付きがないことが好ましい。したがって、Ｒｔｈ＝［（ｎｘ＋ｎｙ）／２−ｎｚ］・ｄ（ただし、ｎｘ、ｎｙはフィルム平面内の主屈折率、ｎｚはフィルム厚方向の屈折率、ｄはフィルム厚みである）で表されるフィルム厚み方向の位相差値が−９０ｎｍ〜＋７５ｎｍである保護フィルムが好ましく用いられる。かかる厚み方向の位相差値（Ｒｔｈ）が−９０ｎｍ〜＋７５ｎｍのものを使用することにより、保護フィルムに起因する偏光板の着色（光学的な着色）をほぼ解消することができる。厚み方向位相差値（Ｒｔｈ）は、さらに好ましくは−８０ｎｍ〜＋６０ｎｍ、特に−７０ｎｍ〜＋４５ｎｍが好ましい。
【０１３５】
保護フィルムとしては、偏光特性や耐久性などの点より、トリアセチルセルロース等のセルロース系ポリマーが好ましい。特にトリアセチルセルロースフィルムが好適である。なお、偏光子の両側に保護フィルムを設ける場合、その表裏で同じポリマー材料からなる保護フィルムを用いてもよく、異なるポリマー材料等からなる保護フィルムを用いてもよい。前記偏光子と保護フィルムとは通常、水系粘着剤等を介して密着している。水系接着剤としては、イソシアネート系接着剤、ポリビニルアルコール系接着剤、ゼラチン系接着剤、ビニル系ラテックス系、水系ポリウレタン、水系ポリエステル等を例示できる。
【０１３６】
前記透明保護フィルムの偏光子を接着させない面には、ハードコート層や反射防止処理、スティッキング防止や、拡散ないしアンチグレアを目的とした処理を施したものであってもよい。
【０１３７】
ハードコート処理は偏光板表面の傷付き防止などを目的に施されるものであり、例えばアクリル系、シリコーン系などの適宜な紫外線硬化型樹脂による硬度や滑り特性等に優れる硬化皮膜を透明保護フィルムの表面に付加する方式などにて形成することができる。反射防止処理は偏光板表面での外光の反射防止を目的に施されるものであり、従来に準じた反射防止膜などの形成により達成することができる。また、スティッキング防止処理は隣接層との密着防止を目的に施される。
【０１３８】
またアンチグレア処理は偏光板の表面で外光が反射して偏光板透過光の視認を阻害することの防止等を目的に施されるものであり、例えばサンドブラスト方式やエンボス加工方式による粗面化方式や透明微粒子の配合方式などの適宜な方式にて透明保護フィルムの表面に微細凹凸構造を付与することにより形成することができる。前記表面微細凹凸構造の形成に含有させる微粒子としては、例えば平均粒径が０．５〜５０μｍのシリカ、アルミナ、チタニア、ジルコニア、酸化錫、酸化インジウム、酸化カドミウム、酸化アンチモン等からなる導電性のこともある無機系微粒子、架橋又は未架橋のポリマー等からなる有機系微粒子などの透明微粒子が用いられる。表面微細凹凸構造を形成する場合、微粒子の使用量は、表面微細凹凸構造を形成する透明樹脂１００重量部に対して一般的に２〜５０重量部程度であり、５〜２５重量部が好ましい。アンチグレア層は、偏光板透過光を拡散して視角などを拡大するための拡散層（視角拡大機能など）を兼ねるものであってもよい。
【０１３９】
なお、前記反射防止層、スティッキング防止層、拡散層やアンチグレア層等は、透明保護フィルムそのものに設けることができるほか、別途光学層として透明保護フィルムとは別体のものとして設けることもできる。
【０１４０】
また位相差板は、視角補償フィルムとして偏光板に積層して広視野角偏光板として用いられる。視角補償フィルムは、液晶表示装置の画面を、画面に垂直でなくやや斜めの方向から見た場合でも、画像が比較的鮮明にみえるように視野角を広げるためのフィルムである。
【０１４１】
このような視角補償位相差板としては、他に二軸延伸処理や直交する二方向に延伸処理等された複屈折を有するフィルム、傾斜配向フィルムのような二方向延伸フィルムなどが用いられる。傾斜配向フィルムとしては、例えばポリマーフィルムに熱収縮フィルムを接着して加熱によるその収縮力の作用下にポリマーフィルムを延伸処理又は／及び収縮処理したものや、液晶ポリマーを斜め配向させたものなどが挙げられる。視角補償フィルムは、液晶セルによる位相差に基づく視認角の変化による着色等の防止や良視認の視野角の拡大などを目的として適宜に組み合わせることができる。
【０１４２】
また良視認の広い視野角を達成する点などより、液晶ポリマーの配向層、特にディスコティック液晶ポリマーの傾斜配向層からなる光学的異方性層をトリアセチルセルロースフィルムにて支持した光学補償位相差板が好ましく用いうる。
【０１４３】
前記のほか実用に際して積層される光学層については特に限定はないが、例えば反射板や半透過板などの液晶表示装置等の形成に用いられることのある光学層を１層または２層以上用いることができる。特に、楕円偏光板または円偏光板に、更に反射板または半透過反射板が積層されてなる反射型偏光板または半透過型偏光板があげられる。
【０１４４】
反射型偏光板は、偏光板に反射層を設けたもので、視認側（表示側）からの入射光を反射させて表示するタイプの液晶表示装置などを形成するためのものであり、バックライト等の光源の内蔵を省略できて液晶表示装置の薄型化を図りやすいなどの利点を有する。反射型偏光板の形成は、必要に応じ透明保護層等を介して偏光板の片面に金属等からなる反射層を付設する方式などの適宜な方式にて行うことができる。
【０１４５】
反射型偏光板の具体例としては、必要に応じマット処理した保護フィルムの片面に、アルミニウム等の反射性金属からなる箔や蒸着膜を付設して反射層を形成したものなどがあげられる。また前記保護フィルムに微粒子を含有させて表面微細凹凸構造とし、その上に微細凹凸構造の反射層を有するものなどもあげられる。前記した微細凹凸構造の反射層は、入射光を乱反射により拡散させて指向性やギラギラした見栄えを防止し、明暗のムラを抑制しうる利点などを有する。また微粒子含有の保護フィルムは、入射光及びその反射光がそれを透過する際に拡散されて明暗ムラをより抑制しうる利点なども有している。保護フィルムの表面微細凹凸構造を反映させた微細凹凸構造の反射層の形成は、例えば真空蒸着方式、イオンプレーティング方式、スパッタリング方式等の蒸着方式やメッキ方式などの適宜な方式で金属を透明保護層の表面に直接付設する方法などにより行うことができる。
【０１４６】
反射板は前記の偏光板の保護フィルムに直接付与する方式に代えて、その透明フィルムに準じた適宜なフィルムに反射層を設けてなる反射シートなどとして用いることもできる。なお反射層は、通常、金属からなるので、その反射面が保護フィルムや偏光板等で被覆された状態の使用形態が、酸化による反射率の低下防止、ひいては初期反射率の長期持続の点や、保護層の別途付設の回避の点などより好ましい。
【０１４７】
なお、半透過型偏光板は、上記において反射層で光を反射し、かつ透過するハーフミラー等の半透過型の反射層とすることにより得ることができる。半透過型偏光板は、通常液晶セルの裏側に設けられ、液晶表示装置などを比較的明るい雰囲気で使用する場合には、視認側（表示側）からの入射光を反射させて画像を表示し、比較的暗い雰囲気においては、半透過型偏光板のバックサイドに内蔵されているバックライト等の内蔵光源を使用して画像を表示するタイプの液晶表示装置などを形成できる。すなわち、半透過型偏光板は、明るい雰囲気下では、バックライト等の光源使用のエネルギーを節約でき、比較的暗い雰囲気下においても内蔵光源を用いて使用できるタイプの液晶表示装置などの形成に有用である。
【０１４８】
また、偏光板は、上記の偏光分離型偏光板の如く、偏光板と２層又は３層以上の光学層とを積層したものからなっていてもよい。従って、上記の反射型偏光板や半透過型偏光板と位相差板を組み合わせた反射型楕円偏光板や半透過型楕円偏光板などであってもよい。
【０１４９】
前記偏光板と位相差板等は、液晶表示装置の製造過程で順次別個に積層することよって形成することができるが、予め積層して楕円偏光板等の光学フィルムとしたのものは、品質の安定性や積層作業性等に優れて液晶表示装置などの製造効率を向上させうる利点がある。
【０１５０】
本発明の光学素子には、粘着層または接着層を設けることもできる。粘着層は、液晶セルへの貼着に用いることができる他、光学層の積層に用いられる。前記光学フィルムの接着に際し、それらの光学軸は目的とする位相差特性などに応じて適宜な配置角度とすることができる。
【０１５１】
接着剤や粘着剤としては特に制限されない。例えばアクリル系重合体、シリコーン系ポリマー、ポリエステル、ポリウレタン、ポリアミド、ポリビニルエーテル、酢酸ビニル／塩化ビニルコポリマー、変性ポリオレフィン、エポキシ系、フッ素系、天然ゴム、合成ゴム等のゴム系などのポリマーをベースポリマーとするものを適宜に選択して用いることができる。特に、光学的透明性に優れ、適度な濡れ性と凝集性と接着性の粘着特性を示して、耐候性や耐熱性などに優れるものが好ましく用いうる。
【０１５２】
前記接着剤や粘着剤にはベースポリマーに応じた架橋剤を含有させることができる。また接着剤には、例えば天然物や合成物の樹脂類、特に、粘着性付与樹脂や、ガラス繊維、ガラスビーズ、金属粉、その他の無機粉末等からなる充填剤や顔料、着色剤、酸化防止剤などの添加剤を含有していてもよい。また微粒子を含有して光拡散性を示す接着剤層などであってもよい。
【０１５３】
接着剤や粘着剤は、通常、ベースポリマーまたはその組成物を溶剤に溶解又は分散させた固形分濃度が１０〜５０重量％程度の接着剤溶液として用いられる。溶剤としては、トルエンや酢酸エチル等の有機溶剤や水等の接着剤の種類に応じたものを適宜に選択して用いることができる。
【０１５４】
粘着層や接着層は、異なる組成又は種類等のものの重畳層として偏光板や光学フィルムの片面又は両面に設けることもできる。粘着層の厚さは、使用目的や接着力などに応じて適宜に決定でき、一般には１〜５００μｍであり、５〜２００μｍが好ましく、特に１０〜１００μｍが好ましい。
【０１５５】
粘着層等の露出面に対しては、実用に供するまでの間、その汚染防止等を目的にセパレータが仮着されてカバーされる。これにより、通例の取扱状態で粘着層に接触することを防止できる。セパレータとしては、上記厚さ条件を除き、例えばプラスチックフィルム、ゴムシート、紙、布、不織布、ネット、発泡シートや金属箔、それらのラミネート体等の適宜な薄葉体を、必要に応じシリコーン系や長鏡アルキル系、フッ素系や硫化モリブデン等の適宜な剥離剤でコート処理したものなどの、従来に準じた適宜なものを用いうる。
【０１５６】
なお本発明において、上記光学素子等、また粘着層などの各層には、例えばサリチル酸エステル系化合物やべンゾフェノール系化合物、ベンゾトリアゾール系化合物やシアノアクリレート系化合物、ニッケル錯塩系化合物等の紫外線吸収剤で処理する方式などの方式により紫外線吸収能をもたせたものなどであってもよい。
【０１５７】
【実施例】
以下に、本発明を実施例をあげて説明するが、本発明は以下に示し実施例に制限されるものではない。
【０１５８】
なお、正面位相差は、面内屈折率が最大となる方向をＸ軸、Ｘ軸に垂直な方向をＹ軸、フィルムの厚さ方向をＺ軸とし、それぞれの軸方向の屈折率をｎｘ、ｎｙ、ｎｚとして、５５０ｎｍにおける屈折率ｎｘ、ｎｙ、ｎｚを自動複屈折測定装置（王子計測機器株式会社製，自動複屈折計ＫＯＢＲＡ２１ＡＤＨ）により計測した値と、位相差層の厚さｄ（ｎｍ）から、正面位相差：（ｎｘ−ｎｙ）×ｄ、厚み方向の位相差：（ｎｘ−ｎｚ）×ｄ、を算出した。傾斜させて測定したときの位相差は、上記自動複屈折測定装置により測定できる。傾斜位相差は：傾斜時の（ｎｘ−ｎｙ）×ｄである。
【０１５９】
Ｎｚ係数は、式：Ｎｚ＝（ｎｘ−ｎｚ）／（ｎｘ−ｎｙ）で定義される。
【０１６０】
なお、反射波長帯域は、反射スペクトルを分光光度計（大塚電子株式会社製、瞬間マルチ測光システム　ＭＣＰＤ−２０００）にて測定し、最大反射率の半分の反射率を有する反射波長帯域とした。
【０１６１】
実施例１
（二次集光素子（Ｙ）の作製）
二次集光素子（Ｙ）として、ＴｉＯ_２　／ＳｉＯ_２　積層枚数１５層の蒸着多層膜バンドパスフィルターを用いた。基材は５０μｍ厚のポリエチレンテレフタレートフィルムを用い、全体厚みは約５３μｍであった。蒸着薄膜の積層厚みの設計図を下記表１に示す。
【０１６２】
【表１】

【０１６３】
（光源）
輝線光源（Ｌ）としてはサイドライト型導光体（導光体は断面がウエッジ型で裏面側にドット印刷が行われた物）を用いたバックライト（スタンレー電気製）１０．　４インチ型を用いた。光源には３波長型冷陰極管を用いた。
【０１６４】
（波長特性）
光源である前記冷陰極管と、二次集光素子（Ｙ）である蒸着多層膜バンドパスフィルターの波長特性は図２２に示す通りである。波長特性の測定は、日立製作所製の分光光度計Ｕ４１００により行なったものである。
【０１６５】
（二次集光素子（Ｙ）の集光特性）
図２３に示すグラフは、図１５の構造にて、二次集光素子（Ｙ）である蒸着多層膜バンドパスフィルターを単独で用いて集光特性を測定したものである。
【０１６６】
図２３に示すグラフには７０°近傍で副次ピークが見られる。これは蒸着多層膜バンドパスフィルター（Ｙ）が斜め入射によりブルーシフトし、緑色光線に対する透過領域が青色光線に対して透過を示し、赤色光線に対する透過領域が緑色光線に対する透過を示すためである。このため斜めからの出射光が強い着色が認められた。さらに用いたバックライトシステムの出射光分布が正面より±６０°以上離れた角度で強い光束を出射しているため着色が目立った。
【０１６７】
（一次集光部（Ｘ）を有するバックライトシステム）
一次集光部（Ｘ）として、プリズムシートを用いた。プリズムシートは３Ｍ製のＢＥＦフィルム（厚み約１８０μｍ，ポリエチレンテレフタレートフィルム製，頂角約９０°，プリズムピッチ５０μｍ）を２枚用いた。
【０１６８】
プリズムシートのプリズム稜線が直交配置となるように、前述の輝線光源（Ｌ）の導光体上に２枚積層した。かかる一次集光部（Ｘ）として、プリズムシートを有するバックライトシステム（ＢＬＳ）は、正面方向に対して、±５０°以内に集光する特性を有していた。
【０１６９】
（集光システム）
前記一次集光部（Ｘ）を有するバックライトシステム（ＢＬＳ）と、二次集光素子（Ｙ）を、図１６の構造にて配置した。図２４は、図１６の構造にて集光特性を計測したものである。液晶セル（ＬＣ）としては、シャープ社製の１０．４インチＴＦＴセルを用いた。また偏光板（ＰＬ）としては日東電工社製のＳＥＧ１４６５ＤＵを用い、液晶セル（ＬＣ）の両側に直交になるように貼りあわせた。二次集光素子（Ｙ）は、偏光板（ＰＬ）に貼り合わせた。なお、以降の実施例において液晶セル（ＬＣ）、偏光板（ＰＬ）としては同じものを用いた。
【０１７０】
図２４から、一次集光により平行化フィルムの大角度での透過成分が劇的に減少し、不愉快な着色を除去することができていることが認められる。一次集光部（Ｘ）の効果により、±５０°程度までバックライトからの出射光が絞り込まれているので７０°近傍の副次透過はカットされて発生しないことが分かる。
【０１７１】
実施例２
（二次集光素子（Ｙ）の作製）
二次集光素子（Ｙ）として、コレステリック液晶ポリマーの薄膜塗工によって作製した、コレステリック液晶バンドパスフィルターを用いた。これは、右円偏光反射の３波長対応バンドパスフィルターと左円偏光反射の３波長対応バンドパスフィルターの組み合わせであり、目的とする３波長のみ垂直方向近傍に対し、光を透過し、斜め入射光線は反射するものである。
【０１７２】
前記コレステリック液晶バンドパスフィルターは、正面透過光線が非偏光である。これは液晶層をバンドパスフィルターとして用いており、コレステリック反射による偏光分離を行わない領域からの透過光線が正面方向へ透過しているためである。したがって、集光特性の測定にあたり、上記二次集光素子（Ｙ）と偏光板（ＰＬ）の間には位相差層は設けずに積層した。
【０１７３】
詳しくは、３波長冷陰極管の発光スペクトル４３５ｎｍ、５４５ｎｍ、６１０ｎｍに対して、選択反射波長域が４４０ｎｍ〜４９０ｎｍ、５５０〜６００ｎｍ、６１５〜７００ｎｍとなる、右円偏光を反射する選択反射円偏光バンドパスフィルターを作製した。用いた液晶材料は、欧州特許出願公開第０８３４７５４号明細書に基づき、選択反射中心波長が４８０ｎｍ、５７０ｎｍ、６５５ｎｍとなる３種のコレステリック液晶ポリマーを作製した。
【０１７４】
コレステリック液晶ポリマーは、下記化１：
【化１】

で表される重合性ネマチック液晶モノマーＡと、下記化２：
【化２】

で表される重合性カイラル剤Ｂを、下記表２に示す割合（重量比）で配合した液晶混合物を重合することにより作製した。前記液晶混合物は、それぞれはテトラヒドロフランに溶解した３３重量％溶液にした後、６０℃環境下にて窒素パージし、反応開始剤（アゾビスイソブチロニトリル，前記混合物に対して０．５重量％）を添加して重合処理を行った。得られた重合物はジエチルエーテルにて再沈分離し精製した。選択反射波長帯域を表２に示す。
【０１７５】
【表２】

【０１７６】
上記コレステリック液晶ポリマーを塩化メチレンに溶解して１０重量％溶液を調製した。当該溶液を、配向基材に、乾燥時の厚みが約１μｍになるようワイヤーバーで塗工した。配向基材として、７５μｍ厚のポリエチレンテレフタレートフィルムを用い、その表面にポリビニルアルコール層を約０．　１μｍ塗工し、レーヨン製ラビング布でラビングしたものを用いた。塗工後、１４０℃で１５分間乾燥した。この加熱処理終了後、液晶を室温にて冷却固定し薄膜を得た。
【０１７７】
上記各コレステリック液晶ポリマーを用いて、上記同様の工程を経て各色の液晶薄膜を作製したのち、イソシアネート系接着剤にて貼り合わせた。その後、ポリエチレンテレフタレート基材を除去し、各液晶層を短波長側から順に３層を積層して約５μｍ厚の液晶複合層を得た。
【０１７８】
一方、重合性カイラル剤Ｂとして、化２とは鏡像異性体となるものを用いたこと以外は上記と全く同様にして、液晶層の３層を積層して、左円偏光を反射する選択反射円偏光バンドパスフィルターを作製した。
【０１７９】
この両者の液晶面同士を、透光性アクリル系粘着材（日東電工製ＮＯ．７，２５μｍ厚）にて貼り合わせた後、支持基材のポリエチレンテレフタレートフィルムを剥離してコレステリック液晶バンドパスフィルター（約３５μｍ厚）を得た。
【０１８０】
（波長特性）
二次集光素子（Ｙ）であるコレステリック液晶バンドパスフィルターの波長特性は図２５に示す通りである。なお、図２１に示すグラフは、図１５の構造にて、前記二次集光素子（Ｙ）であるコレステリック液晶バンドパスフィルターを単独で用いて集光特性を測定したものである。
【０１８１】
（一次集光部（Ｘ）を有するバックライトシステム）
実施例１と同様の、一次集光部（Ｘ）として、プリズムシートを２枚積層したバックライトシステム（ＢＬＳ）を用いた。
【０１８２】
（集光システム）
前記一次集光部（Ｘ）を有するバックライトシステム（ＢＬＳ）と、二次集光素子（Ｙ）を、図１６の構造にて配置した。図２６は、図１６の構造にて集光特性を計測したものである。
【０１８３】
図２６から、一次集光により平行化フィルムの大角度での透過成分が劇的に減少し、不愉快な着色を除去することができていることが認められる。一次集光部（Ｘ）の効果により、±５０°程度までバックライトからの出射光が絞り込まれているので７０°近傍の副次透過はカットされて発生しないことが分かる。
【０１８４】
実施例３
（二次集光素子（Ｙ）の作製）
二次集光素子（Ｙ）として、偏光の選択反射の波長帯域が互いに重なる２枚の円偏光型反射偏光子（ａ１）の間に位相差板（ｂ１）を設けた偏光素子を用いた。
【０１８５】
円偏光型反射偏光子（ａ１）としては、日東電工社製のＮＩＰＯＣＳフィルム（ＰＣＦ４００）のコレステリック液晶層を用いた。
【０１８６】
次いで、下記方法にて、正面位相差が略０、斜め方向で位相差を発生する位相差層（ｂ１：ネガティブＣプレート）を重合性液晶にて作製した。重合性メソゲン化合物として、ＢＡＳＦ社製のＬＣ２４２、重合性カイラル剤として、ＢＡＳＦ社製のＬＣ７５６を用いた。重合性メソゲン化合物と重合性カイラル剤は、得られるコレステリック液晶の選択反射中心波長が約３５０ｎｍとなるように、重合性メソゲン化合物／重合性カイラル剤の混合比（重量比）＝１１／８８、とした。得られたコレステリック液晶の選択反射中心波長は３５０ｎｍであった。
【０１８７】
具体的な製法は、以下の通りである。重合性カイラル剤と重合性メソゲン化合物をシクロペンタンにて溶解（３０重量％）し、反応開始剤（チバスペシャルティケミカルズ社製のイルガキュア９０７，前記混合物に対して１重量％）を添加した溶液を調製した。溶液には、界面活性剤ＢＹＫ−　３６１（ビッグケミジャパン製）を前記混合物に対して０．　０１重量％添加した。配向基板は、東レ製のポリエチレンテレフタレートフィルム：ルミラー（厚さ７５μｍ）をラビング布にて配向処理したものを用いた。
【０１８８】
前記溶液をワイヤーバーにて乾燥時塗布厚みが７μｍ厚にて塗布し、９０℃で２分間乾燥した後、等方性転移温度１３０℃まで一旦加熱した後、徐冷した。均一な配向状態を保持し、８０℃の環境にて紫外線照射（１０ｍＷ／平方ｃｍ×１分間）にて硬化してネガティブＣプレート（ｂ１）を得た。このネガティブＣプレート（ｂ１）の位相差を測定したところ、５５０ｎｍの波長の光に対して正面方向では２ｎｍ、３０°傾斜させた時の位相差は約１９０ｎｍ（＞λ／８）であった。
【０１８９】
上記で得られた円偏光型反射偏光子（ａ１）の上部に透光性アクリル系粘着剤（日東電工社製，ＮＯ．７，２５μｍ厚）を用いて、ネガティブＣプレート（ｂ１）を接着した後、基材を剥離除去した。この上に、さらに円偏光型反射偏光子（ａ１）を積層転写し、偏光素子を得た。当該偏光素子を、二次集光素子（Ｙ）とした。
【０１９０】
実施例３の二次集光素子（Ｙ）は、可視光帯域全域で偏光分離機能を有しているので正面透過光線はコレステリック液晶の偏光分離機能により円偏光化している。したがって、液晶セル（ＬＣ）のバックライト側の偏光板（ＰＬ）と二次集光素子（Ｙ）の間には１／４波長板（Ｂ）を偏光板（ＰＬ）の偏光軸に対して４５°の傾斜で挿入し、透光性アクリル系粘着材（日東電工製ＮＯ．７，２５μｍ）にて貼り合わせた。円偏光を直線偏光化し、偏光板への透過特性を高めるためである。
【０１９１】
（一次集光部（Ｘ）を有するバックライトシステム）
一次集光部（Ｘ）として、プリズムシートを用いた。プリズムシートは３Ｍ製のＢＥＦフィルム（厚み約１８０μｍ，ポリエチレンテレフタレートフィルム製，頂角約９０°，プリズムピッチ５０μｍ）を２枚用いた。
【０１９２】
プリズムシートのプリズム稜線が直交配置となるように、ドット印刷されたアクリル製の導光板（茶谷産業製のサイドライト型バックライト）上に２枚積層した。かかる一次集光部（Ｘ）として、プリズムシートを有するバックライトシステムは、±５５°以内に集光する特性を有していた。
【０１９３】
（二次集光素子（Ｙ）の集光特性）
図２７に示すグラフは、図１７の構造にて二次集光素子（Ｙ）である偏光素子（Ａ）を単独で用いて集光特性を測定したものである。図２７に示すグラフには５０°以上の外側で漏れ光線が認められる。
【０１９４】
（集光システム）
前記一次集光部（Ｘ）を有するバックライトシステム（ＢＬＳ）と、二次集光素子（Ｙ）を、図１８の構造にて配置した。図２８は、図１８の構造にて集光特性を計測したものである。なお、図２７、図２８の集光特性の測定はＥＬＤＩＭ社製Ｅｚ−Ｃｏｎｔｒａｓｔにより行なったものである。
【０１９５】
図２８より、一次集光により平行化フィルムの大角度での透過成分が劇的に減少し、不愉快な着色を除去することができていることが認められる。一次集光部（Ｘ）により光源からの５０°以上の角度での出射光線が減少し、二次集光素子（Ｙ）を通過する光線が無くなり、中央の二次集光部分のみ残る。すなわち正面のみ明るく見えて斜め方向は漆黒で着色は見えない。
【０１９６】
実施例４
（二次集光素子（Ｙ）の作製）
二次集光素子（Ｙ）として、偏光の選択反射の波長帯域が互いに重なる２枚の直線偏光型反射偏光子（ａ２）の間に、位相差板（ｂ１）を有し、位相差板（ｂ１）の両側には、正面位相差が略λ／４である層（ｂ２）を有する偏光素子を用いた。
【０１９７】
直線偏光型反射偏光子（ａ２）としては、３Ｍ製のＤＢＥＦを用いた。位相差板（ｂ１）は、実施例３におけるネガティブＣプレートの作製法に準じて作製した。得られたネガティブＣプレート（ｂ１）は厚み８μｍ、位相差を測定したところ、５５０ｎｍの波長の光に対して正面方向では０ｎｍ、３０°傾斜させた時の位相差は約２２０ｎｍ（＞λ／４）であった。このネガティブＣプレートをサンドイッチする位相差板（ｂ２）として日東電工製ＮＲＦフィルム（正面位相差１４０ｎｍ）を用い、上下の直線偏光型反射偏光子（ａ２）に対して、各々の軸と４５°（−４５°）の角度で貼り合わせ、５枚を積層した。積層は透光性アクリル系粘着材（日東電工製ＮＯ．７，２５μｍ厚）にて貼り合わせた。
【０１９８】
（一次集光部（Ｘ）を有するバックライトシステム）
一次集光部（Ｘ）を有するバックライトシステム（ＢＬＳ）として、表面にマイクロプリズムアレイを作製した断面ウエッジ型アクリル導光体・サイドライト型バックライト（ＩＢＭ製ノートＰＣ　ＴｈｉｎｋＰａｄより取り出し）を用いた。一次集光部（Ｘ）を有するバックライトシステム（ＢＬＳ）は、光源からの出射光を、正面方向に対して、±５０°以内に１次集光していた。
【０１９９】
（二次集光素子（Ｙ）の集光特性）
図２９に示すグラフは、図１９の構造にて二次集光素子（Ｙ）である偏光素子（Ａ）単独による集光特性を測定したものである。図２９に示すグラフには正面方向に対して、±５０°以上の外側で漏れ光線が認められる。なお、図１９の構造において、光源（Ｌ）は、ハクバ製ライトボックス（直下型バックライト，拡散光源）を用いた。
【０２００】
（集光システム）
前記一次集光部（Ｘ）を有するバックライトシステム（ＢＬＳ）と、二次集光素子（Ｙ）を、図２０の構造にて配置した。図３０は、図２０の構造にて集光特性を計測したものである。
【０２０１】
図３０から、一次集光により平行化フィルムの大角度での透過成分が劇的に減少し、不愉快な着色を除去することができていることが認められる。
【０２０２】
比較例
集光フィルムとして、実施例２のコレステリック液晶バンドパスフィルターを用いた。ドット印刷された導光板上に配置した。集光特性は図２に示す通りであり、副次透過の強いピークが見られる。
【図面の簡単な説明】
【図１】偏光素子（Ａ）の平行光化の基本原理の一例を示す概念図である。
【図２】図１、３、４、６、８に示す、各光線の状態を説明するものである。
【図３】直線偏光の円偏光化を示す概念図である。
【図４】偏光素子（Ａ）の平行光化の基本原理の一例を示す概念図である。
【図５】直線偏光型反射偏光素子（ａ２）を用いた平行光化の各層の配置角度を示す一例である。
【図６】偏光素子（Ａ）の平行光化の基本原理の一例を示す概念図である。
【図７】直線偏光型反射偏光素子（ａ２）を用いた平行光化の各層の配置角度を示す一例である。
【図８】偏光素子（Ａ）の平行光化の基本原理の一例を示す概念図である。
【図９】直線偏光型反射偏光素子（ａ２）を用いた平行光化の各層の配置角度を示す一例である。
【図１０】モアレの直接解を示す概念図である。
【図１１】本発明の集光システムの概略図の一例である。
【図１２】本発明の集光システムの概略図の一例である。
【図１３】本発明の透過型液晶表示装置の概略図の一例である。
【図１４】本発明の透過型液晶表示装置の概略図の一例である。
【図１５】実施例１、２において、二次集光素子（Ｙ）単独による集光特性を測定したときの透過型液晶表示装置の概略図である。
【図１６】実施例１、２の透過型液晶表示装置の概略図である。
【図１７】実施例３において、二次集光素子（Ｙ）単独による集光特性を測定したときの透過型液晶表示装置の概略図である。
【図１８】実施例３の透過型液晶表示装置の概略図である。
【図１９】実施例４において、二次集光素子（Ｙ）単独による集光特性を測定したときの透過型液晶表示装置の概略図である。
【図２０】実施例４の透過型液晶表示装置の概略図である。
【図２１】実施例２の二次集光素子（Ｙ）単独による集光特性を示すグラフである。
【図２２】実施例１の二次集光素子（Ｙ）の波長特性を示すグラフである。
【図２３】実施例１の二次集光素子（Ｙ）単独による集光特性を示すグラフである。
【図２４】実施例１の、一次集光部（Ｘ）を有するバックライトシステムと、二次集光素子（Ｙ）を組み合わせた場合の集光特性を示すグラフである。
【図２５】実施例２の二次集光素子（Ｙ）の波長特性を示すグラフである。
【図２６】実施例２の、一次集光部（Ｘ）を有するバックライトシステムと、二次集光素子（Ｙ）を組み合わせた場合の集光特性を示すグラフである。
【図２７】実施例３の二次集光素子（Ｙ）の波長特性を示すグラフである。
【図２８】実施例３の、一次集光部（Ｘ）を有するバックライトシステムと、二次集光素子（Ｙ）を組み合わせた場合の集光特性を示すグラフである。
【図２９】実施例４の二次集光素子（Ｙ）の波長特性を示すグラフである。
【図３０】実施例４の、一次集光部（Ｘ）を有するバックライトシステムと、二次集光素子（Ｙ）を組み合わせた場合の集光特性を示すグラフである。
【符号の説明】
Ｘ　　　一次集光部
Ｙ　　　二次集光素子
Ｌ　　　光源
ＢＬＳ　バックライトシステム
ａ１　円偏光型反射偏光子
ａ２　直線偏光型反射偏光子
ｂ　　位相差層
Ａ　　偏光素子
Ｂ　　λ／４板
ＬＣ　液晶セル
ＰＬ　偏光板[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light collection system and a transmission type liquid crystal display device.
[0002]
[Prior art]
An optical film having an angle dependence with respect to transmittance and reflectance, such as a vapor deposition type bandpass filter using Brewster's angle (for example, see Patent Document 1) and a selective reflection characteristic of cholesteric liquid crystal using Bragg reflection. (See, for example, Patent Literature 2, Patent Literature 3, Patent Literature 4, etc.), a technique of condensing a diffused light source in the front direction is known. By using these optical films, the reflectance changes depending on the incident angle, and a filter that transmits light only to the front can be manufactured by appropriate optical design. Light rays that cannot be transmitted are reflected without being absorbed and returned to the light source side, recycled, and highly efficient light-collecting characteristics can be obtained.
[0003]
In addition, the parallel light conversion of these systems can be designed to have a high degree of parallelism, and it is possible to collect and collimate light in a narrow range of ± 20 ° or less from the front direction. This is a level that is difficult with a conventional backlight system using a prism sheet or a microdot array alone.
[0004]
However, the shielding ratio of these light-collecting films was not perfect, and residual transmitted light in oblique directions was observed. If the wavelength bandwidth to be shielded is narrow, secondary transmission appears in an oblique direction, which becomes a waste in the oblique direction, and causes problems such as coloring due to different transmittance for each wavelength. there were.
[0005]
For example, in the case of a bright line type light condensing element using a combination of a bandpass filter and a bright line type light source, only the front side transmits the necessary bright line and shields the oblique direction, but has three wavelengths to transmit. In this case, there is a problem that a region that transmits a green ray shifts to a blue bright line region and transmits blue light. In addition, there is a problem that a region transmitting a red light beam shifts to a green bright line region and transmits green light.
[0006]
Also, a method of condensing and collimating light using a bright line light source and an interference film bandpass filter has been proposed (for example, see Patent Document 5, Patent Document 6, Patent Document 7, etc.). However, these patent documents all mention only the effect near the front, and have not solved the problem of the secondary transmission at a large incident angle.
[0007]
In a total reflection type light-collecting device using a combination of a reflective polarizer and a retardation plate, there is no influence of the bright line. However, there is a problem similar to that of the bright line type light condensing element in that a blue shift of the reflection characteristic occurs when the incident angle increases, and in order to maintain sufficient shielding properties, the reflection characteristic in the infrared region at the time of front incidence is required. Required. Furthermore, the reflective polarizer has to function over the entire wavelength band so as to cover the characteristics of the phase difference plate sandwiched therebetween.
[0008]
Due to these problems, the above two types of light condensing elements could not sufficiently cut incident light from a large angle by themselves. Therefore, unpleasant coloring was observed because the wavelength characteristics of the transmission components were not uniform.
[0009]
It is possible to shield the secondary transmission in the design of the light collection film. However, in the case of realizing with a multilayer laminated structure of materials having different refractive indexes and phase differences, the number of laminated layers is increased, which causes a cost increase. In addition, when cholesteric liquid crystal is used, the thickness of the liquid crystal layer increases, which causes a cost increase. In addition to these cost increases, there was also a concern about an increase in the thickness of the optical functional layer, an adverse effect on reliability and appearance caused by internal residual stress, and the like.
[0010]
[Patent Document 1]
German Patent Application Publication No. 3836955
[Patent Document 2]
JP-A-2-158289
[Patent Document 3]
JP-A-6-235900
[Patent Document 4]
JP-A-10-321025
[Patent Document 5]
U.S. Pat. No. 4,984,872
[Patent Document 6]
US Patent Application Publication No. 2002/36735
[Patent Document 7]
U.S. Pat. No. 6,307,604
[0011]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a light-collecting system capable of effectively shielding oblique directions, suppressing unpleasant coloring, having good display, and reducing costs. .
[0012]
Still another object of the present invention is to provide a transmission type liquid crystal display device using the light collection system.
[0013]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have found the following transmissive liquid crystal display device, and have completed the present invention. That is, the present invention is as follows.
[0014]
1. A backlight system having a light source and a primary light collector (X) capable of collecting light emitted from the light source within ± 60 ° with respect to the front direction;
A light-collecting system comprising a light-collecting film having no pattern structure as a secondary light-collecting element (Y).
[0015]
2. The light collection system according to claim 1, wherein the backlight system having the primary light collection part (X) is a light source and a microprism sheet array arranged on the light source.
[0016]
3. The light collection system according to claim 1, wherein the backlight system having the primary light collection part (X) is a microprism processing light guide combined with a light source.
[0017]
4. The light collection system according to claim 1, wherein the backlight system having the primary light collection part (X) is a microdot processed light guide combined with a light source.
[0018]
5. Since the light-condensing film used as the secondary light-condensing element (Y) does not have a pattern structure, when the light-condensing film is applied to a liquid crystal cell and optically observed from the surface side (viewing side), 5. The light-collecting system according to any one of the above items 1 to 4, wherein moiré and interference fringes do not occur with the regular pattern of the optical member.
[0019]
6. A light-condensing film used as a secondary light-condensing element (Y) has a retardation layer (b) disposed between at least two reflective polarizers (a) in which the wavelength bands of polarized light selective reflection overlap each other. The light-collecting system according to any one of the above items 1 to 5, wherein the polarizing element (A) is a polarizing element (A).
[0020]
7. The reflective polarizer (a) is a circularly polarized reflective polarizer (a1) that transmits certain circularly polarized light and selectively reflects opposite circularly polarized light,
The retardation layer (b) forms a retardation layer (b1) having a front retardation (normal direction) of substantially zero and an incident light inclined at an angle of 30 ° or more with respect to the normal direction and having a wavelength of λ / 8 or more. 7. The light-collecting system according to the above 6, wherein the light-collecting system has:
[0021]
8. The reflection polarizer (a) is a linear polarization type reflection polarizer (a2) that transmits one of orthogonal linearly polarized lights and selectively reflects the other, and
The phase difference layer (b) has a front phase difference (normal direction) of substantially zero, and a phase difference layer (b1) of λ / 4 or more with respect to incident light incident at an angle of 30 ° or more with respect to the normal direction. Have
On both sides of the phase difference layer (b1), a layer (b2) having a front phase difference of approximately λ / 4 is provided between the layer and the linear polarization type reflective polarizer (a2);
The incident side layer (b2) is at an angle of 45 ° (−45 °) ± 5 ° with respect to the polarization axis of the incident side linear polarization type reflective polarizer (a2).
The emission-side layer (b2) has an angle of −45 ° (+ 45 °) ± 5 ° with respect to the polarization axis of the emission-side linear polarization type reflective polarizer (a2).
The incident side layer (b2) and the exit side layer (b2) have an arbitrary angle formed by their slow axes,
7. The light-collecting system according to the item 6, wherein the light-collecting system is disposed.
[0022]
9. The reflection polarizer (a) is a linear polarization type reflection polarizer (a2) that transmits one of orthogonal linearly polarized lights and selectively reflects the other, and
The retardation layer (b) has two biaxial retardation layers (b3) having a front retardation of approximately λ / 4 and an Nz coefficient of 2 or more,
The incident-side layer (b3) has a slow axis direction at an angle of 45 ° (−45 °) ± 5 ° with respect to the polarization axis of the incident-side linear polarization type reflective polarizer (a2).
The emission-side layer (b3) has a slow axis direction at an angle of -45 ° (+ 45 °) ± 5 ° with respect to the polarization axis of the emission-side linearly polarizing reflective polarizer (a2).
The incident side layer (b3) and the exit side layer (b3) have an arbitrary angle formed by their slow axes,
7. The light-collecting system according to the item 6, wherein the light-collecting system is disposed.
[0023]
10. The reflection polarizer (a) is a linear polarization type reflection polarizer (a2) that transmits one of orthogonal linearly polarized lights and selectively reflects the other, and
The retardation layer (b) has one biaxial retardation layer (b4) having a front retardation of approximately λ / 2 and an Nz coefficient of 1.5 or more,
The slow axis direction of the incident side layer is at an angle of 45 ° (−45 °) ± 5 ° with respect to the polarization axis of the linear polarization type reflective polarizer (a2) on the incident side.
The direction of the slow axis of the emission-side layer is −45 ° (+ 45 °) ± 5 ° with respect to the polarization axis of the emission-side linear polarization type reflective polarizer (a2).
The polarization axes of the two linearly polarizing reflective polarizers (a2) are substantially orthogonal,
7. The light-collecting system according to the item 6, wherein the light-collecting system is disposed.
[0024]
11. The light-collecting system according to any one of the above items 1 to 5, wherein the light-collecting film used as the secondary light-collecting element (Y) is a band-pass filter, and the light source has a bright line spectrum.
[0025]
12. 12. The light-collecting system according to the above item 11, wherein the band-pass filter is a vapor-deposited multilayer band-pass filter.
[0026]
13. 12. The light-collecting system according to the above item 11, wherein the band-pass filter is a cholesteric liquid crystal band-pass filter.
[0027]
14． 12. The light-collecting system according to the above item 11, wherein the band-pass filter is a band-pass filter made of a stretched film of a multilayer laminated extruded base material of resin materials having different refractive indexes.
[0028]
15. 12. The light-collecting system according to the above item 11, wherein the band-pass filter is a band-pass filter composed of a multilayer thin film precision coated film of resin materials having different refractive indexes.
[0029]
16. A light-collecting system according to any one of the above 1 to 15,
A liquid crystal cell through which the collimated light passes,
Polarizing plates arranged on both sides of the liquid crystal cell,
A transmissive liquid crystal display device characterized by containing at least:
[0030]
(Action)
The light-collecting system comprises: a backlight system having a primary light-collecting portion (X) within ± 60 ° with respect to a front direction of the light emitted from the light source; By combining the secondary light-collecting element (Y) with a strong aperture, the transmission component at a large angle is dramatically reduced, and unpleasant coloring can be removed.
[0031]
Generally, a secondary condensing element (Y) using a bright line type light source and an interference filter or a secondary condensing element (A) using a polarizing element (A) combining a reflective polarizer (a) and a retardation layer (b) ( The secondary transmission of Y) occurs at a large angle when viewed from the normal direction. Therefore, according to the present invention, as shown in FIGS. 11 and 12, a light collection system is provided in which a backlight system (BLS) having a primary light collection unit (X) and a secondary light collection element (Y) are combined. In FIG. 11, the primary condensing section (X) is provided separately from the light source (L). A prism sheet or the like can be given as the primary condensing section (X) shown in FIG. In FIG. 12, the primary condensing section (X) is incorporated in the light source (L) to form a backlight (BLS). The primary condensing section (X) performs primary condensing of the light emitted from the light source, and reduces incident light from a large oblique angle. Thus, the secondary light-collecting element (Y) is less susceptible to the leaked light in the region where the shielding ability is insufficient, and it is possible to reduce unpleasant coloring in an oblique direction. In addition, by the secondary focusing by the secondary focusing element (Y), in a region with high parallelism near the front, it is possible to further narrow down from the primary focused light beam to obtain high-purity parallel light. FIG. 13 and FIG. 14 show a transmission type liquid crystal display device using the light collecting system of FIG. 11 and FIG. Polarizing plates (PL) are arranged on both sides of the liquid crystal cell (LC). The above light-collecting system is arranged such that the secondary light-collecting element (Y) is on the liquid crystal cell (LC) side. 13 and 14, the secondary light-collecting element (Y) is bonded to the liquid crystal cell (LC).
[0032]
In general, the conventional primary light condensing means has a pattern structure, and the light can be condensed within a range of about ± 50 °, and beyond that, it is hard to stop. On the other hand, the secondary focusing means was sharply stopped down, but leakage of secondary peaks was observed.
[0033]
In the light collection system of the present invention, the primary light collection required for the primary light collection part (X) is within ± 60 °, more preferably within ± 50 °. This is because, as shown in FIG. 21, the secondary transmission of the light-collecting film used as the secondary light-collecting element (Y) generally appears at 60 to 70 °. By combining a light source that does not substantially generate an outgoing light beam at an angle at which the secondary transmission component occurs, the secondary transmission is effectively shielded, and the secondary transmission component is out of the display viewing angle range originally required for the secondary transmission. The emitted light can be efficiently reused. Note that the graph shown in FIG. 21 is obtained by measuring the light condensing characteristics when the cholesteric liquid crystal bandpass filter described in Example 2 is used as the secondary light condensing element (Y) in the structure of FIG. is there. Further, the same liquid crystal cell (LC), light source (L) and polarizing plate (PL) as in Example 2 were used. Note that the measurement of the light-collecting characteristics is obtained by measuring the emission light characteristics using Ez-Contrast manufactured by ELDIM. The vertical axis in FIG. 21 represents the luminance (candela), and the horizontal axis represents the angle of the light emitted from the light source with respect to the front direction. The measurement of the light-collecting characteristics in the present invention is all measured by such a measuring method.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
The light collection system of the present invention has a backlight system having a light source (L) and a primary light collection part (X). As the light source (L), any of a direct type backlight and a side type backlight can be adopted. The side backlight has a light guide plate. The primary condensing part (X) may be arranged on the light source (L) or may be incorporated in the light source (L).
[0035]
The primary condensing section (X) is, for example, a micro prism sheet array. Further, a microprism-processed light guide combined with a light source, a microdot-processed light guide combined with a light source, and the like can be given. These can be combined. Specifically, as a backlight system having a primary light condensing part (X), for example, a microprism array / microdot array is engraved on the surface of a wedge-shaped light guide, and the range of emitted light is narrowed to near the front. A light guide plate with high directivity or a backlight system in which emitted light is narrowed in the front direction by a microprism sheet is preferably used.
[0036]
The backlight system having the primary light condensing part (X) is not particularly limited as long as it has a characteristic of condensing the light emitted from the light source within ± 60 ° with respect to the front direction. Therefore, the backlight system having the primary light condensing part (X) has a light condensing characteristic, such as a light source type, a light guide plate type, a prism light condensing sheet serving as the primary light condensing part (X), and the like. The material and the like are not particularly limited, and the arrangement and the like can be appropriately set.
[0037]
Whether or not the backlight system having the primary condensing portion (X) has a characteristic of condensing the emitted light from the light source within ± 60 ° with respect to the front direction is determined as follows. . That is, for a backlight system having a primary light-collecting part (X), the light-collecting characteristics are measured in the same manner as described above (however, the primary light-collecting element (X) is used instead of the secondary light-collecting element (Y)). ). Then, with respect to the luminance value when the angle of the emitted light with respect to the front direction is changed, based on the maximum luminance value in the front direction, the case where the angle falling to half the value is within the range of ± 60 °, Light was condensed within ± 60 °.
[0038]
On the other hand, the light-collecting film used as the secondary light-collecting element (Y) has no pattern structure. Since the light-collecting film does not have a pattern structure, when the light-collecting film is applied to a liquid crystal cell and optically observed from the front side (viewing side), the regular pattern of other optical members and the moire pattern are observed. And no interference fringes.
[0039]
When the light-condensing film used as the secondary light-condensing element (Y) is optically observed from the surface side (viewing side), it is determined whether or not moiré or interference fringes occur with the regular pattern of other optical members. For example, for a member in which a polarizing plate is attached to both sides of a liquid crystal cell (TFT-liquid crystal display cell) and the light-condensing film is attached to the backlight side, the judgment is made by rotating the member and visually observing the member. be able to.
[0040]
The material and method of the light-condensing film used as the secondary light-condensing element (Y) are not particularly limited. For example, when combined with a light source having an emission line spectrum, a band-pass filter is used as the light-collecting film. On the other hand, when there is no limitation on the type of light source, the light-collecting film may include a retardation layer (b) between at least two reflective polarizers (a) in which the wavelength bands of polarized light selective reflection overlap each other. ) Can be used. Although these are both optical systems in which secondary transmission occurs at around 60 to 70 °, the structure of the present invention can prevent secondary transmission.
[0041]
Examples of the band-pass filter include a vapor-deposited multilayer film band-pass filter, a cholesteric liquid crystal band-pass filter, a multi-layer laminated extruded base material of a resin material having a different refractive index, and a multilayer thin film of a resin material having a different refractive index. A band pass filter made of a precision coated film or the like is preferably used.
[0042]
Hereinafter, the polarizing element (A) will be described. The mechanism of the simultaneous manifestation of the light-collecting property and the enhancement of the brightness when the polarizing element (A) is used will be described below with reference to the present invention with an ideal model.
[0043]
FIG. 1 is an explanatory diagram showing the principle when a circularly polarizing reflective polarizer (a1) is used as the reflective polarizer (a). In FIG. 1, as the polarizing element (A), a circularly polarizing reflective polarizer (a1), a retardation layer (b1), and a circularly polarizing reflective polarizer (a1) are arranged in this order from the backlight side (lower side). Have been.
[0044]
The operation principle is as described in 1) to 3).
1) An incident light beam is divided into a transmitted light beam and a reflected light beam by a circular polarization type reflective polarizer (a1) that separates polarized light by reflection. Therefore, there is no absorption loss.
2) A special retardation plate (b1) having a front phase difference of substantially zero and a phase difference in an oblique direction is used, and a front incident light beam is passed through.
3) Incident light rays in oblique directions are not absorbed but returned as reflected light. The reflected light is repeatedly reflected until it becomes a transmitted light.
[0045]
The retardation plate (b1) used here is generally called a negative C plate (negative retardation plate) or a positive C plate (positive retardation plate). These retardation plates (b1) have a property that the phase difference is close to 0 in the vertical direction (normal direction) and a phase difference is generated when the phase plate is tilted. As a typical negative C plate, specifically, a biaxially stretched polycarbonate film, a polyethylene terephthalate film, or a cholesteric liquid crystal is used. A film in which the selective reflection wavelength band is set shorter than visible light or a discotic liquid crystal is parallel to the surface. Examples thereof include an oriented film and a film obtained by in-plane orientation of an inorganic crystal compound having a negative retardation. A typical positive C plate is, for example, a homeotropically aligned liquid crystal film.
[0046]
The circular polarization type reflective polarizer (a1) is one in which the cholesteric liquid crystal is mainly oriented, and the twist pitch is adjusted so that the selective reflection wavelength band covers the visible light region / light source emission wavelength band (for example, the selective reflection center wavelength). A stack of a plurality of different films, or a single layer in which the pitch changes in the thickness direction) is used. As the circularly polarized reflective polarizer (a1) arranged on both sides of the retardation plate (b1) in FIG. 1, those having the same direction of transmitted circularly polarized light are preferably used.
[0047]
The circularly-polarized reflective polarizer (a1) and the retardation layer (b1) can be used without specifying the bonding direction because there is almost no axis in the in-plane direction. For this reason, the angle range for narrowing down the parallel light has isotropic / symmetric characteristics.
[0048]
In the following, as will be described with reference to the drawings, the symbol (r) in each drawing indicates natural light, (ii) indicates circularly polarized light, and (iii) indicates linearly polarized light, as shown in FIG. (Ii) In circularly polarized light, the arrows are opposite in (ii) -1 and -2. This means that the direction of rotation is reversed. (Iii) -1 and -2 mean that the polarization axes are orthogonal to each other.
[0049]
A description will be given of changes in each ray of the parallel light when the circular polarizer (a1) is used as the reflective polarizer (a) shown in FIG.
1) Among the natural light (r1) supplied from the backlight, one that is perpendicularly incident on the circularly polarized reflective polarizer (a1) is polarized and separated into transmitted light (r3) and reflected light (r2). The direction of rotation of the circularly polarized light is opposite to that of the transmitted light and the reflected light.
2) The transmitted light (r3) passes through the retardation layer (b1).
3) Further, the transmitted light (r4) passes through the circularly polarized reflective polarizer (a1).
4) The transmitted light (r5) is used for a liquid crystal display device disposed thereon.
5) On the other hand, among the natural light (r6) supplied from the backlight, one that is obliquely incident on the circularly-polarized reflective polarizer (a1) is polarized and separated into transmitted light (r8) and reflected light (r7). You. The direction of rotation of the circularly polarized light is opposite to that of the transmitted light and the reflected light.
6) The transmitted light (r8) is affected by the phase difference when passing through the phase difference layer (b1). Given a phase difference value of 波長 wavelength, the circularly polarized light turns in the opposite direction and becomes the opposite direction. Therefore, the transmitted light (r8) reverses its rotation after transmitting through the retardation layer (b1).
7) The transmitted light (r9) is emitted with its rotation inverted due to the effect of the phase difference.
8) The transmitted light (r9) that has been reversely rotated is reflected by the circular polarization type reflective polarizer (a1). It is known that the direction of rotation of circularly polarized light is generally reversed when reflected. ("Polarization and its Applications", WA Sharkiff, Polarized Light: Production and Use, by WA Sharkliffe, (Harvard University Press, Cambridge, Mass., 1966)). However, as an exception, it is known that the rotation direction does not change in the case of reflection at the cholesteric liquid crystal layer. Here, since the reflection is performed on the cholesteric liquid crystal surface, the rotation direction of the circularly polarized light of the transmitted light (r9) and the reflected light (r10) does not change.
9) The reflected light (r10) is affected by the phase difference when passing through the phase difference layer (b1).
10) The rotation of the transmitted light (r11) is inverted due to the influence of the phase difference.
11) The transmitted light (r11) that has been reversely rotated and returned in the same direction as the transmitted light (r8) passes through the circularly-polarized reflective polarizer (a1).
12) The reflected light (r2, r7, r12) returns to the backlight side and is recycled. These return light rays are repeatedly reflected by a diffuser or the like arranged in a backlight while changing the traveling direction and the direction of polarized light at random until the light rays can be transmitted in the vicinity of the normal direction of the polarizing element (A) again. Contribute to improvement.
13) The transmitted circularly polarized light (r5) can be converted to linearly polarized light by disposing a λ / 4 plate, so that it can be used without causing absorption loss in the liquid crystal display device.
[0050]
As for the transmittance and the reflectance of the circular polarization type reflective polarizer (a1) using the cholesteric liquid crystal, the wavelength characteristic of the transmitted light shifts to the shorter wavelength side with respect to the incident light in the oblique direction. Therefore, it is necessary to have sufficient polarization characteristics / phase difference characteristics on the long wavelength side outside the visible light range in order to function sufficiently for light rays incident at a deep angle. Ideally and theoretically, the retardation layer (b1) used in this system should have a phase difference of exactly 波長 wavelength in the oblique direction. The element (a1: cholesteric liquid crystal layer) has some properties as a negative retardation plate. Therefore, in order to obtain the function of the present invention, the optical function can be exhibited if the phase difference layer (b1) has a phase difference of about 1/8 wavelength or more in the oblique direction.
[0051]
When the reflection polarizer (a) is a linear polarization type reflection polarizer (a2), for example, when a C plate (a retardation layer (b1)) is used alone as the retardation layer (b), a C plate is used. The optical axis for a light beam that is incident obliquely on the light beam is always orthogonal to the light beam direction. Therefore, no phase difference is exhibited and no polarization conversion is performed. Therefore, when the linear polarization type reflection polarizer (a2) is used, the slow axis direction is set at 45 ° or −45 ° with respect to the polarization axis of the linear polarization type reflection polarizer (a2) on both sides of the C plate. Λ / 4 plate (b2) having Thus, the linearly polarized light is converted into circularly polarized light by the λ / 4 plate (b2), then converted into reverse circularly polarized light by the phase difference of the C plate, and the circularly polarized light is converted into linearly polarized light again by the λ / 4 plate (b2). Can be converted.
[0052]
FIG. 3 is a conceptual diagram in which natural light is polarization-separated into linearly polarized light by a linear polarization type reflection polarizer (a2), and further converted into circularly polarized light by a λ / 4 plate (b2).
[0053]
FIG. 4 is a conceptual diagram in the case where a linear polarization type reflection polarizer (a2) is used as the reflection polarizer (a). In FIG. 4, as the polarizing element (A), from the backlight side (lower side), a linear polarization type reflective polarizer (a2), a λ / 4 plate (b2), a retardation layer (b1), a λ / 4 plate ( b2), a linear polarization type reflective polarizer (a2) is arranged in this order.
[0054]
FIG. 5 is an example of a bonding angle of each film in the parallel light conversion system shown in FIG. The double-headed arrow shown in the linear polarization type reflection polarizer (a2) is the polarization axis, and the double-headed arrow shown in the λ / 4 plate (b2) is the slow axis. C plate: On both sides of the retardation layer (b1), the polarization axis of the linear polarization type reflection polarizer (a2) and the slow axis of the λ / 4 plate (b2) are at an angle of 45 ° (−45 °) ± 5. ° placed. These combinations are shown as set1 and set2, respectively. The angle formed by the axes of the λ / 4 plate (b2) on the incident side and the exit side is arbitrary.
[0055]
If the angle 45 ° (−45 °) between the polarization axis of the linear polarization type reflection polarizer (a2) and the slow axis of the λ / 4 plate (b2) is maintained, set1 and set2 may be rotated. . C plate: Since the retardation layer (b1) has no axial direction in the plane, it can be arranged without specifying the angle.
[0056]
The change of each light beam of the parallel light shown in FIGS. 4 and 5 will be described below.
1) Part of the natural light (r14) supplied from the backlight is perpendicularly incident on the linear polarization type reflective polarizer (a2).
2) The linearly polarized reflective polarizer (a2) transmits linearly polarized light (r15) and reflects linearly polarized light (r16) in the orthogonal direction.
3) The linearly polarized light (r15) passes through the λ / 4 plate (b2) and is converted into circularly polarized light (r17).
4) The circularly polarized light (r17) passes through the retardation layer (b1).
5) The circularly polarized light (r18) passes through the λ / 4 plate (b2) and is converted into linearly polarized light (r19).
6) The linearly polarized light (r19) passes through the linearly polarized reflection polarizer (a2).
7) The linearly polarized light (r20) enters the liquid crystal display device disposed thereon and is transmitted without loss.
8) On the other hand, a part of the natural light (r21) supplied from the backlight is obliquely incident on the linear polarization type reflective polarizer (a2).
9) The linearly polarized reflective polarizer (a2) transmits linearly polarized light (r22) and reflects linearly polarized light (r23) in the orthogonal direction.
10) The linearly polarized light (r22) passes through the λ / 4 plate (b2) and is converted into circularly polarized light (r24).
11) When passing through the retardation layer (b1), the circularly polarized light (r24) receives a phase difference of 波長 wavelength, and the rotation is reversed.
12) The inverted circularly polarized light (r25) passes through the λ / 4 plate (b2) and is converted into linearly polarized light (r26).
13) The linearly polarized light (r26) is reflected by the linearly polarized reflection polarizer (a2) to become linearly polarized light (r27).
14) The linearly polarized light (r27) passes through the λ / 4 plate (b2) and is converted into circularly polarized light (r28).
15) When passing through the retardation layer (b1), the circularly polarized light (r28) receives a phase difference of 1/2 wavelength, and the rotation is reversed.
16) The inverted circularly polarized light (r29) passes through the λ / 4 plate (b2) and is converted into linearly polarized light (r30).
17) The linearly polarized light (r30) passes through the linearly polarized reflection polarizer (a2).
18) The reflected light (r16, r23, r31) is returned to the backlight side and recycled.
[0057]
Originally, in an ideal system, the angle between the slow axis of the λ / 4 plate (b2) described here and the polarization axis of the linear polarization type reflection polarizer (a2) is 45 °. The characteristics of the actual linear polarization type reflection polarizer (a2) and the λ / 4 plate (b2) are not perfect in the visible light range, and there is a subtle change for each wavelength. If this is ignored and the layers are stacked at 45 °, coloring may be observed.
[0058]
Therefore, if the color tone is compensated by slightly changing the angle, the entire system can be optimized rationally. On the other hand, if the angle deviates greatly, other problems such as a decrease in transmittance will occur. Therefore, in reality, it is desirable to stop the adjustment within a range of about ± 5 degrees.
[0059]
The transmittance and the reflectance of the linear polarization type reflection polarizer (a2) are such that the wavelength characteristic of the transmitted light shifts to the shorter wavelength side with respect to the incident light in the oblique direction. The circularly polarized reflection polarizer using the cholesteric liquid crystal. Same as (a1). Therefore, it is necessary to have sufficient polarization characteristics / phase difference characteristics on the long wavelength side outside the visible light range in order to function sufficiently for light rays incident at a deep angle.
[0060]
The linear polarization type reflection polarizer (a2) has a smaller negative phase difference characteristic than the cholesteric liquid crystal. Accordingly, the phase difference in the oblique direction (30 ° inclination) of the retardation layer (b1) used sandwiched between the linear polarization type reflection polarizers (a2) is smaller than that of the circular polarization type reflection polarizer (a1) using the cholesteric liquid crystal. It is slightly larger than the case, preferably 1/4 wavelength or more.
[0061]
In addition to the above, when the reflection polarizer (a) is a linear polarization type reflection polarizer (a2), the C plate: the retardation layer (b1) is sandwiched between two λ / 4 plates (b2). The same applies to the case where two biaxial retardation layers (b3) having a front retardation of approximately λ / 4 and a thickness direction retardation of approximately λ / 2 or more are arranged instead of using the structure. The effect can be obtained. Such a biaxial retardation layer (b3) satisfies the above requirements if the Nz coefficient is 2 or more.
[0062]
FIG. 6 is a conceptual diagram in a case where a linear polarization type reflection polarizer (a2) is used as the reflection polarizer (a) and a biaxial retardation layer (b3) is used. In FIG. 6, as the polarizing element (A), from the backlight side (lower side), a linear polarization type reflective polarizer (a2), a biaxial retardation layer (b3), a biaxial retardation layer (b3), The linear polarization type reflection polarizer (a2) is arranged in order.
[0063]
FIG. 7 is an example of a bonding angle of each film in the parallel light conversion system shown in FIG. The double-headed arrow shown in the linear polarization type reflection polarizer (a2) is the polarization axis, and the double-headed arrow shown in the retardation layer (b1) is the slow axis. The polarization axis of the linear polarization type reflection polarizer (a2) and the slow axis of the biaxial retardation layer (b3) are arranged at an angle of 45 ° (−45 °) ± 5 °. These combinations are shown as set1 and set2, respectively.
[0064]
For easy explanation of the optical path, an example is shown in which the polarization axes of the upper and lower linearly polarizing reflective polarizers (a2) are parallel and the slow axes of the biaxial retardation layer (b3) are orthogonal. The angle formed by the slow axes of the upper and lower biaxial retardation layers (b3) is arbitrary. If the angle 45 ° (−45 °) between the polarization axis of the linear polarization type reflection polarizer (a2) and the slow axis of the biaxial retardation layer (b3) is maintained, set1 and set2 are rotated. Is also good.
[0065]
The change of each ray of the parallel light shown in FIGS. 6 and 7 in the above example will be described.
1) Part of the natural light (r32) supplied from the backlight is perpendicularly incident on the linear polarization type reflective polarizer (a2).
2) The linear polarization type reflective polarizer (a2) transmits linearly polarized light (r33) and reflects linearly polarized light (r34) in the orthogonal direction.
3) The linearly polarized light (r33) passes through two biaxial retardation layers (b3) having a front retardation of approximately １ ／ wavelength. Here, since the slow axes of the two biaxial retardation layers (b3) are orthogonal to each other at 90 °, the front retardation is zero. Therefore, the linearly polarized light (r35) passes through.
4) The linearly polarized light (r35) passes through the linearly polarized reflection polarizer (a2).
5) The linearly polarized light (r36) enters the liquid crystal display device and is transmitted without loss.
6) On the other hand, a part of the natural light (r37) supplied from the backlight is obliquely incident on the linear polarization type reflective polarizer (a2).
7) The linear polarization type reflective polarizer (a2) transmits linearly polarized light (r38) and reflects linearly polarized light (r39) in the orthogonal direction.
8) The linearly polarized light (r38) is obliquely incident on the two biaxial retardation layers (b3). Since the biaxial retardation layer (b3) has a front retardation of 1/4 wavelength and an Nz coefficient of 2 or more, the biaxial retardation layer (b3) has transmitted through the two biaxial retardation layers (b3) due to a change in retardation in the thickness direction. The linearly polarized light (r40) changes its polarization axis direction by 90 °.
9) The linearly polarized light (r40) enters the linearly polarized reflection polarizer (a2).
10) Since the upper and lower linearly polarized reflective polarizers (a2) have the same direction of the polarization axis, the linearly polarized light (r40) becomes reflected light (r41).
11) When the reflected light (r41) passes through the two biaxial retardation layers (b3), it is affected by the phase difference similarly to 8), and the linearly polarized light (r42) whose polarization axis direction is rotated by 90 °. ).
12) The linearly polarized light (r42) passes through the linearly polarized reflection polarizer (a2).
13) The reflected light (r34, r39, r43) is returned to the backlight side and recycled.
The polarizing element (A) shown in FIG. 6 and FIG. 7 has two biaxial retardation layers (b3) having a front retardation of about １ ／ wavelength and a Nz coefficient of 2 or more. This is almost the same as the case where a three-layer laminate having a structure in which a C plate and a retardation layer (b1) are sandwiched between two λ / 4 plates (b2) as shown in FIGS. 4 and 5 is used. Characteristics can be generated. Therefore, the number of layers is smaller than that of the above-mentioned polarizing element (A), and the productivity is slightly better.
[0066]
Originally, in an ideal system, the angle between the slow axis of the retardation layer (b3) described here and the polarization axis of the linear polarization type reflective polarizer (a2) is 45 °. Are not perfect in the visible light range, and there is a subtle change for each wavelength of the linearly polarized reflection polarizer (a2) and the retardation layer (b3). If this is ignored and the layers are stacked at 45 °, coloring may be observed.
[0067]
Therefore, if the color tone is compensated by slightly changing the angle, the entire system can be optimized rationally. On the other hand, if the angle deviates greatly, other problems such as a decrease in transmittance will occur. Therefore, in practice, it is desirable to stop the adjustment within a range of about ± 5 °.
[0068]
The transmittance and the reflectance of the linear polarization type reflection polarizer (a2) are such that the wavelength characteristic of the transmitted light shifts to the shorter wavelength side with respect to the incident light in the oblique direction. The circularly polarized reflection polarizer using the cholesteric liquid crystal. Same as (a1). Therefore, it is necessary to have sufficient polarization characteristics / phase difference characteristics on the long wavelength side outside the visible light range in order to function sufficiently for light rays incident at a deep angle.
[0069]
When the reflection polarizer (a) is a linear polarization type reflection polarizer (a2), the retardation layer (b) has a front phase difference of approximately λ / 2 and a thickness direction phase difference of λ /. A similar effect can be obtained by disposing a biaxial retardation layer (b4) having two or more layers. Such a biaxial retardation layer (b4) satisfies the above requirements if the Nz coefficient is 1.5 or more.
[0070]
FIG. 8 is a conceptual diagram in the case where a linear polarization type reflection polarizer (a2) is used as the reflection polarizer (a) and a biaxial retardation layer (b4) is used. In FIG. 8, as the polarizing element (A), from the backlight side (lower side), a linear polarization type reflection polarizer (a2), a biaxial retardation layer (b4), and a linear polarization type reflection polarizer (a2) are used. They are arranged in this order.
[0071]
FIG. 9 is an example of a bonding angle of each film in the parallel light conversion system shown in FIG. The double-headed arrow shown in the linear polarization type reflective polarizer (a2) is the polarization axis, and the double-headed arrow shown in the retardation layer (b4) is the slow axis. The polarization axes of the upper and lower linearly polarized reflective polarizers (a2) are arranged substantially orthogonally. The slow axis of the biaxial retardation layer (b4) and the polarization axis of the linear polarization type reflective polarizer (a2) are arranged at an angle of 45 ° (−45 °) ± 5 °.
[0072]
The change of each ray of the parallel light shown in FIGS. 8 and 9 will be described below.
1) Part of the natural light (r47) supplied from the backlight is perpendicularly incident on the linear polarization type reflective polarizer (a2).
2) The linear polarization type reflective polarizer (a2) transmits linearly polarized light (r48) and reflects linearly polarized light (r49) in the orthogonal direction.
3) The linearly polarized light (r48) passes through the biaxial retardation layer (b4) having a front phase difference of approximately 波長 wavelength, is converted into linearly polarized light (r50), and the direction of the polarization axis is rotated by 90 °.
4) The linearly polarized light (r50) passes through the linearly polarized reflection polarizer (a2).
5) The transmitted linearly polarized light (r51) enters the liquid crystal display device and is transmitted without loss.
6) On the other hand, a part of the natural light (r52) supplied from the backlight is obliquely incident on the linear polarization type reflective polarizer (a2).
7) The linear polarization type reflection polarizer (a2) transmits the linearly polarized light (r53), and reflects the linearly polarized light (r54) in the orthogonal direction.
8) The linearly polarized light (r53) is obliquely incident on the biaxial retardation layer (b4). Since the biaxial retardation layer (b4) has a front retardation of about 波長 wavelength and an Nz coefficient of 2 or more, the direction of the polarization axis is the same as that of the linearly polarized light (r53) due to the phase difference in the thickness direction. It transmits with the linearly polarized light (r55) in the state.
9) The transmitted linearly polarized light (r55) is reflected by the linearly polarized reflective polarizer (a2) to become reflected light (r56).
10) The reflected light (r56) enters the retardation layer (b4). This also transmits without changing the axial direction.
11) The transmitted linearly polarized light (r57) passes through the linearly polarized reflective polarizer (a2) to become linearly polarized light (r58).
12) The reflected light (r49, r54, r58) is returned to the backlight side and recycled.
[0073]
The polarizing element (A) shown in FIGS. 8 and 9 has one biaxial retardation layer (b4) having a front retardation of about 略 wavelength and a Nz coefficient of 1.5 or more. 4 and 5, a C plate: a three-layer laminate having a structure in which a retardation layer (b1) is sandwiched between two λ / 4 plates (b2) as shown in FIGS. Almost the same characteristics can be generated. Therefore, the number of layers is smaller than that of the above-mentioned polarizing element (A), and the productivity is slightly better. Furthermore, the productivity is superior to the case of using a two-layer laminate as shown in FIGS.
[0074]
Originally, in an ideal system, the angle between the slow axis of the retardation layer (b4) and the polarization axis of the linear polarization type reflection polarizer (a2) is 45 ° in theory in an ideal system. Are not perfect in the visible light range, and there is a subtle change for each wavelength of the linearly polarized reflection polarizer (a2) and the retardation layer (b4). If this is ignored and the layers are stacked at 45 °, coloring may be observed.
[0075]
Therefore, if the color tone is compensated by slightly changing the angle, the entire system can be optimized rationally. On the other hand, if the angle deviates greatly, other problems such as a decrease in transmittance will occur. Therefore, in practice, it is desirable to stop the adjustment within a range of about ± 5 °.
[0076]
The transmittance and the reflectance of the linear polarization type reflection polarizer (a2) are such that the wavelength characteristic of the transmitted light shifts to the shorter wavelength side with respect to the incident light in the oblique direction. The circularly polarized reflection polarizer using the cholesteric liquid crystal. Same as (a1). Therefore, it is necessary to have sufficient polarization characteristics / phase difference characteristics on the long wavelength side outside the visible light range in order to function sufficiently for light rays incident at a deep angle.
[0077]
As shown in FIGS. 1 to 9 described above, the polarizing element (A) converts the light beam incident at an incident angle of 30 ° from the normal direction into the axially polarized light reflected by the two reflective polarizers (a). The polarizing element (A) has a total reflection function at an incident angle of 30 °, and does not transmit light near the incident angle of 30 °. Substantially, the polarizing element (A) has a high transmittance in a range of about ± 15 to 20 ° from the normal direction, and light rays having an incident angle higher than that are reflected and reused. For this reason, the transmitted light from the light source is concentrated within the above range, and is condensed and parallelized.
[0078]
The collimated backlight obtained in this way has a feature that it is thinner than the prior art and a light source with high parallelism can be easily obtained. In addition, since parallel light is formed by polarized light reflection, which has essentially no absorption loss, the reflected non-parallel light component returns to the backlight side, is scattered and reflected, and recycling, in which only the parallel light component is extracted, is recycled. Repeatedly, substantially high transmittance and high light use efficiency can be obtained.
[0079]
The phase difference anisotropy control type parallelizing means used in the present invention does not allow the in-plane fine structure to be seen from the plane direction by optical observation, and the fineness used in the liquid crystal pixels, the black matrix, and the parallelizing means. There is no interference with the film having the structure, the glare-treated surface on the outermost surface of the liquid crystal display device, and the like, and has a feature that it does not cause moire.
[0080]
Moiré, as shown in FIG. 10, is a light and shade pattern having a lower frequency than a grid that is visible when grids formed in different layers are superposed at an angle.
[0081]
The pitch of moiré fringes is given by
(Equation 1)

Is represented by In Equation 1, S1: the first grating pitch, S2: the second grating pitch, S3: the moiré fringe pitch, α: the angle between the first grating and the second grating.
[0082]
When the maximum value of the intensity I of the moire fringes obtained by superimposing different gratings is Imax and the minimum value is Imin, and the visibility (V: visibility) of the moire fringes is calculated, the formula: V = (Imax−Imin) ) / (Imax + Imin). In order to reduce the contrast, it is desired that the angle between the gratings is sufficiently large and close to orthogonal. However, it is difficult to satisfy the requirements when the number of layers having the lattice is three or more. Therefore, it can be seen that the reduction of the layer having the lattice structure is effective for suppressing the moire phenomenon.
[0083]
(Reflective polarizer (a))
It is desirable to achieve total reflection of light having a wavelength of around 550 nm, which has high visibility, from the viewpoint of improving brightness, and the selective reflection wavelength of the reflective polarizer (a) should be at least 550 nm ± 10 nm. It is desirable that they overlap.
[0084]
For example, in a backlight using a wedge-type light guide plate, which is widely used in liquid crystal display devices, the angle of light emitted from the light guide plate is about 60 ° from the normal direction. The amount of blue shift at this angle extends to about 100 nm. Therefore, when a three-wavelength cold-cathode tube is used for the backlight, since the red emission line spectrum is 610 nm, it is understood that the selective reflection wavelength needs to reach at least the longer wavelength side than 710 nm. Since the selective reflection wavelength bandwidth required on the long wavelength side largely depends on the angle and wavelength of the incident light from the light source as described above, the long wavelength end is arbitrarily set according to the required specifications.
[0085]
When the backlight light source emits only a specific wavelength, for example, in the case of a colored cold-cathode tube, it is sufficient that only the obtained bright line can be shielded.
[0086]
Also, if the light emitted from the backlight is narrowed down to some extent from the beginning by designing microlenses, dots, prisms, etc. processed on the surface of the body, the transmitted light at a large incident angle can be ignored. The selective reflection wavelength does not need to be largely extended to the longer wavelength side. It can be designed appropriately according to the combination member and light source type.
[0087]
From this viewpoint, the reflective polarizer (a) may be a completely identical combination, or one may have reflection at all wavelengths of visible light and the other may partially reflect.
[0088]
(Circularly polarized reflective polarizer (a1))
As the circular polarization type reflective polarizer (a1), for example, a cholesteric liquid crystal material is used. In the circularly polarized reflective polarizer (a1), the central wavelength of selective reflection is determined by λ = np (n is the refractive index of the cholesteric material, and p is the chiral pitch). For obliquely incident light, the selective reflection wavelength shifts blue, so that the overlapping wavelength region is preferably wider.
[0089]
In the case where the circularly polarized reflective polarizer (a1) is a cholesteric material, even if a combination of different types (right-handed and left-handed) is tilted at a front phase difference of λ / 2 with the same concept, if the phase difference is zero or λ, Although a similar polarizer can be obtained, it is not preferable because problems such as anisotropy and coloring due to the azimuth of the inclined axis occur. From such a viewpoint, a combination of the same types (right-twisted, left-twisted) is preferable. However, coloring can be suppressed by canceling out the combination of the upper and lower cholesteric liquid crystal molecules or the C-plate having different wavelength dispersion characteristics. .
[0090]
As the cholesteric liquid crystal constituting the circular polarization type reflective polarizer (a1), an appropriate one may be used, and there is no particular limitation. For example, a liquid crystal polymer that exhibits cholesteric liquid crystallinity at a high temperature, or a polymerizable liquid crystal obtained by polymerizing a liquid crystal monomer and a chiral agent and an alignment assistant as required by irradiation with ionizing radiation such as an electron beam or ultraviolet light or heat, or a polymerizable liquid crystal thereof. And mixtures thereof. The liquid crystal properties may be either lyotropic or thermotropic, but it is desirable that the liquid crystal be a thermotropic liquid crystal from the viewpoint of easy control and easy formation of a monodomain.
[0091]
The cholesteric liquid crystal layer can be formed by a method according to a conventional alignment treatment. For example, a film of polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, polyetherimide, etc. is formed on a support base material having a birefringence retardation as small as possible, such as triacetyl cellulose or amorphous polyolefin, to form rayon. Alignment film rubbed with cloth or SiO ₂ An obliquely deposited layer, or a base material using an oriented base material such as polyethylene terephthalate or polyethylene naphthalate as an alignment film, or the base material surface is treated with a fine abrasive typified by a rubbing cloth or bengara. , A substrate on which fine irregularities having a fine alignment regulating force are formed on the surface, or a substrate on which an alignment film that generates a liquid crystal regulating force by light irradiation such as an azobenzene compound is formed on the base film, and the like. The liquid crystal polymer is spread on the alignment film and heated to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature. A method of forming a fixed solidified layer may, for example, be mentioned.
[0092]
Further, at the stage when the alignment state is formed, the structure may be fixed by irradiation with energy such as ultraviolet rays or ion beams. The base material having a small birefringence may be used as it is as a liquid crystal layer support. When the birefringence is large or the requirement for the thickness of the polarizing element (A) is strict, the liquid crystal layer can be peeled off from the alignment substrate and used as appropriate.
[0093]
The liquid crystal polymer film is formed by, for example, applying a solution of the liquid crystal polymer in a solvent by 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, a gravure printing method, or the like. It can be carried out by a method in which a layer is developed and, if necessary, a drying treatment is performed. Examples of the solvent include chlorine solvents such as methylene chloride, trichloroethylene and tetrachloroethane; ketone solvents such as acetone, methyl ethyl ketone and cyclohexanone; aromatic solvents such as toluene; cyclic alkanes such as cycloheptane; -Methylpyrrolidone, tetrahydrofuran and the like can be used as appropriate.
[0094]
In addition, a method in which a heated melt of a liquid crystal polymer, preferably a heated melt in a state exhibiting an isotropic phase, is developed in accordance with the above, and further developed into a thin layer and solidified while maintaining the melting temperature as necessary. can do. This method does not use a solvent, so that the liquid crystal polymer can be developed even by a method with good sanitation of the working environment. When the liquid crystal polymer is developed, a method of superimposing a cholesteric liquid crystal layer via an alignment film or the like may be employed as needed for the purpose of thinning or the like.
[0095]
Further, if necessary, these optical layers can be peeled off from the support base material / alignment base material used at the time of film formation and transferred to another optical material for use.
[0096]
(Linear polarization type reflective polarizer (a2))
Examples of the linearly-polarized reflective polarizer (a2) include a grid-type polarizer, a multilayer thin-film laminate of two or more layers made of two or more materials having a difference in refractive index, and a vapor-deposited multilayer thin film having a different refractive index used for a beam splitter and the like. A birefringent multilayer thin film laminate of two or more layers of two or more materials having birefringence, a stretched two or more resin laminate using two or more resins having birefringence, and linearly polarized light. One that is separated by being reflected / transmitted in an orthogonal axis direction is exemplified.
[0097]
For example, polyethylene naphthalate, polyethylene terephthalate, a material that generates a phase difference by stretching typified by polycarbonate, an acrylic resin typified by polymethyl methacrylate, a norbornene resin typified by ARTON manufactured by JSR, etc. A resin obtained by uniaxially stretching a small amount of resin alternately as a multilayer laminate can be used.
[0098]
(Retardation layer (b))
The retardation layer (b1) disposed between the circular polarization type reflection polarizer (a1) and the linear polarization type reflection polarizer (a2) has a phase difference of almost zero in the front direction and is 30 ° from the normal direction. It has a phase difference of λ / 8 or more with respect to incident light at an angle. The front phase difference is desirably λ / 10 or less because the purpose is to maintain polarized light that is vertically incident.
[0099]
The incident light from an oblique direction is appropriately determined by the angle of total reflection so as to be efficiently polarized and converted. For example, in order to achieve total reflection at an angle of about 60 ° from the normal, the phase difference measured at 60 ° may be determined so as to be about λ / 2. However, the transmitted light by the circularly polarized reflective polarizer (a1) changes its polarization state also due to the birefringence of the circularly polarized reflective polarizer (a1) itself. The phase difference measured at that angle of the plate may be a value smaller than λ / 2. Since the phase difference of the C plate monotonically increases as the incident light is inclined, an effective total reflection is caused when the incident light is inclined at an angle of 30 ° or more. You only have to.
[0100]
In the case where the polarizing element (A) of the present invention is designed so as to effectively block light having an incident angle of 30 ° from the front, substantially enough transmitted light can be obtained in a region having an incident angle of about 20 °. Is declining. When limited to light rays in this area, only light rays in an area showing good display of a general TN liquid crystal display device are transmitted. Although it varies depending on conditions such as the type of liquid crystal in the cell, the alignment state, and the pretilt angle of the TN liquid crystal display device to be used, it is used for expanding the viewing angle in the present invention because gradation inversion and sharp deterioration of contrast do not occur. Standard. The phase difference value of the retardation layer may be made larger in order to narrow down to only the front light, or the phase difference value may be made smaller and the focusing narrowed down on the assumption that a compensating phase difference plate is combined with the TN liquid crystal. .
[0101]
The material of the retardation layer (b1) is not particularly limited as long as it has the above optical characteristics. For example, a cholesteric liquid crystal having a selective reflection wavelength other than the visible light region (380 nm to 780 nm) having a fixed planar alignment state, a rod-shaped liquid crystal having a fixed homeotropic alignment state, a discotic liquid crystal having a columnar alignment or a nematic alignment. And a biaxially oriented polymer film in which a negative uniaxial crystal is oriented in a plane.
[0102]
As the C plate, for example, a C plate in which the planar alignment state of a cholesteric liquid crystal having a selective reflection wavelength other than the visible light region (380 nm to 780 nm) is fixed, the visible light region is colored as the cholesteric liquid crystal selective reflection wavelength It is desirable that there is no. Therefore, it is necessary that the selective reflection light is not in the visible region. The selective reflection is uniquely determined by the cholesteric chiral pitch and the refractive index of the liquid crystal. The value of the center wavelength of the selective reflection may be in the near-infrared region, but it is more preferably in the ultraviolet region of 350 nm or less because it is affected by optical rotation and a somewhat complicated phenomenon occurs. The formation of the cholesteric liquid crystal layer is performed in the same manner as the formation of the cholesteric layer in the reflective polarizer described above.
[0103]
A C-plate with a fixed homeotropic alignment state is formed by polymerizing a liquid crystalline thermoplastic resin or liquid crystal monomer that exhibits nematic liquid crystallinity at high temperature and an alignment aid, if necessary, with irradiation of ionizing radiation such as electron beams or ultraviolet rays or heat. Polymerizable liquid crystal or a mixture thereof is used. The liquid crystal properties may be either lyotropic or thermotropic. However, from the viewpoint of easy control and easy formation of a monodomain, it is desirable that the liquid crystal be a thermotropic liquid crystal. The homeotropic alignment can be obtained, for example, by applying the birefringent material on a film on which a vertical alignment film (such as a long-chain alkylsilane) is formed, and developing and fixing a liquid crystal state.
[0104]
As a C-plate using discotic liquid crystal, a discotic liquid crystal material having a negative uniaxial property such as a phthalocyanine or triphenylene compound having a molecular spread in a plane as a liquid crystal material is used as a nematic phase or a columnar phase. It is expressed and fixed. The negative uniaxial inorganic layered compound is described in detail in, for example, JP-A-6-82777.
[0105]
A C-plate utilizing biaxial orientation of a polymer film is a method of biaxially stretching a polymer film having a positive refractive index anisotropy in a well-balanced manner, a method of pressing a thermoplastic resin, and a method of cutting a parallel-oriented crystal. It can be obtained by a method or the like.
[0106]
When the linear polarization type reflection polarizer (a2) is used, the retardation layer (b1) has a phase difference of approximately zero in the front direction and λ / λ for incident light at an angle of 30 ° from the normal direction. Those having a phase difference of 4 or more are used. On both sides of the retardation layer (b1), linearly polarized light is once converted into circularly polarized light by using a λ / 4 plate (b2) having a front retardation of approximately λ / 4, and then the same method as the above-described circularly polarizing plate is used. Can be turned into parallel light. The configuration cross section and the arrangement of each layer in this case are as shown in FIG. 3, FIG. 4, and FIG. In this case, the angle between the slow axis of the λ / 4 plate (b2) and the polarization axis of the linear polarization type reflection polarizer (a2) is as described above, and the axis angle between the λ / 4 plates (b2) is arbitrary. Can be set to
[0107]
Specifically, a λ / 4 plate is used as the retardation layer (b2). As the λ / 4 plate, an appropriate retardation plate according to the purpose of use is used. The λ / 4 plate can control optical characteristics such as retardation by laminating two or more kinds of retardation plates. As the retardation plate, polycarbonate, norbornene-based resin, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyarylate, a birefringent film obtained by stretching a film made of an appropriate polymer such as polyamide or Examples include an alignment film made of a liquid crystal material such as a liquid crystal polymer, and an alignment layer of a liquid crystal material supported by a film.
[0108]
A retardation plate that functions as a λ / 4 plate in a wide wavelength range such as a visible light region is, for example, a retardation layer that functions as a λ / 4 plate for light-colored light having a wavelength of 550 nm and a retardation that exhibits other retardation characteristics. It can be obtained by a method of superimposing a layer, for example, a retardation layer functioning as a half-wave plate. Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement film may be composed of one or more retardation layers.
[0109]
A similar effect can be obtained by arranging two biaxial retardation layers (b3) having a front retardation of approximately λ / 4 and a thickness direction retardation of λ / 2 or more. . The biaxial retardation layer (b3) satisfies the above requirements if the Nz coefficient is approximately 2 or more. The configuration cross section and the arrangement of each layer in this case are as shown in FIGS. In this case, the slow axis with the biaxial retardation layer (b3) and the polarization axis of the linear polarization type reflective polarizer (a2) are as described above, and the axial angle between the biaxial retardation layers (b3) Can be set arbitrarily.
[0110]
It is preferable that the front phase difference is approximately λ / 4, which falls within a range of about λ / 4 ± 40 nm, more preferably ± 15 nm, for light having a wavelength of 550 nm.
[0111]
Similar effects can be obtained by using one biaxial retardation layer (b4) having a front retardation of approximately λ / 2 and a thickness direction retardation of λ / 2 or more. The biaxial retardation layer (b4) has an Nz coefficient of about 1. If it is 5 or more, the above requirement is satisfied. The configuration cross section and the arrangement of each layer in this case are as shown in FIGS. In this case, the relationship between the axis angles of the upper and lower linearly polarizing reflective polarizers (a2) and the central biaxial retardation layer (b4) becomes the designated angle and is uniquely determined.
[0112]
The front phase difference of approximately λ / 2 is preferably about λ / 2 ± 40 nm for light having a wavelength of 550 nm, and more preferably within a range of ± 15 nm.
[0113]
Specifically, as the biaxial retardation layers (b3) and (b4), a birefringent plastic material such as polycarbonate or polyethylene terephthalate is biaxially stretched, or a liquid crystal material is uniaxially oriented in a planar direction. A hybrid oriented material further oriented in the thickness direction is used. A liquid crystal material in which the liquid crystal material is uniaxially homeotropically aligned is also possible, and is performed in the same manner as in the method of forming a cholesteric liquid crystal film. However, it is necessary to use a nematic liquid crystal material instead of a cholesteric liquid crystal.
[0114]
(Arrangement of diffuse reflection plate)
It is desirable to dispose a diffuse reflection plate below the light guide plate as the light source (on the side opposite to the surface where the liquid crystal cells are disposed). The main component of the light beam reflected by the collimating film is an oblique incident component, which is specularly reflected by the collimating film and returned toward the backlight. Here, if the rear-side reflector has high specular reflectivity, the reflection angle is preserved, and the light cannot be emitted in the front direction, resulting in light loss. Therefore, it is desirable to dispose a diffuse reflector in order to increase the scattered reflection component in the front direction without preserving the reflection angle of the reflected return light beam.
[0115]
(Arrangement of diffusion plate)
It is also desirable to provide an appropriate diffuser between the collimating film and the backlight source. This is because the light reuse efficiency is increased by scattering the obliquely incident and reflected light rays in the vicinity of the backlight light guide and scattering a part of the light rays in the vertical incidence direction.
[0116]
The diffusion plate to be used can be obtained by a method of embedding fine particles having different refractive indices in a resin, in addition to a material having a surface irregular shape. This diffusion plate may be sandwiched between the collimating film and the backlight, or may be bonded to the collimating film.
[0117]
When the liquid crystal cell to which the collimating film is attached is disposed close to the backlight, Newton rings may occur in the gap between the film surface and the backlight. By disposing a diffusion plate having surface irregularities on the surface, the generation of Newton rings can be suppressed. Further, a layer having both a concavo-convex structure and a light-diffusing structure may be formed on the surface of the collimating film in the present invention.
[0118]
(Arrangement of viewing angle expansion layer)
The viewing angle expansion in the liquid crystal display device of the present invention, combined with a parallelized backlight, diffuses light beams having good display characteristics near the front obtained from the liquid crystal display device and is uniform within the entire viewing angle. It is obtained by obtaining good display characteristics.
[0119]
As the viewing angle expanding layer used here, a diffusion plate having substantially no back scattering is used. The diffusion plate can be provided by a diffusion adhesive. The arrangement location is on the viewing side of the liquid crystal display device, but it can be used on either side of the polarizing plate. However, in order to prevent the influence of pixel bleeding and the like and the decrease in contrast due to slightly remaining back scattering, it is desirable to provide the layer as close to the cell as possible, such as between the polarizing plate and the liquid crystal cell. In this case, a film that does not substantially eliminate polarized light is desirable. For example, a fine particle-dispersed diffusion plate as disclosed in JP-A-2000-347006 and JP-A-2000-347007 is preferably used.
[0120]
When the viewing angle enlarging layer is located outside the polarizing plate on the viewing side of the liquid crystal cell, the parallelized light passes through the liquid crystal cell and the polarizing plate. It is not necessary to use a plate. In the case of an STN liquid crystal cell, it is only necessary to use a retardation film in which only the front characteristics are well compensated. In this case, since the viewing angle widening layer has an air surface, it is possible to adopt a type based on a refraction effect due to the surface shape.
[0121]
On the other hand, when a viewing angle widening layer is inserted between the polarizing plate and the liquid crystal cell, the light is diffused at the stage of transmission through the polarizing plate. In the case of a TN liquid crystal, it is necessary to compensate for the viewing angle characteristics of the polarizer itself. In this case, it is preferable to insert a retardation plate for compensating the viewing angle characteristics of the polarizing plate between the polarizing plate and the viewing angle widening layer. In the case of the STN liquid crystal, it is preferable to insert a retardation plate for compensating the viewing angle characteristics of the polarizing plate in addition to the front retardation compensation of the STN liquid crystal.
[0122]
In the case of a viewing angle widening film having a regular structure inside, such as a conventional microlens array film or hologram film, the microlens of a black matrix of a liquid crystal display device or a conventional parallel light conversion system of a backlight Moire was likely to occur due to interference with microstructures such as arrays / prism arrays / louvers / micromirror arrays. However, in the parallel light-converting film of the present invention, the regular structure is not visually recognized in the plane, and there is no regular modulation in the outgoing light beam. Therefore, it is not necessary to consider the compatibility with the viewing angle widening layer and the arrangement order. Therefore, the viewing angle expanding layer is not particularly limited as long as it does not cause interference / moire with the pixel black matrix of the liquid crystal display device, and the options are wide.
[0123]
In the present invention, the light-scattering plate as described in JP-A-2000-347006 and JP-A-2000-347007 has substantially no back scattering as the viewing angle widening layer and does not eliminate polarized light. And a haze of 80% to 90% are preferably used. In addition, even if it has a regular structure inside, such as a hologram sheet, a microprism array, a microlens array, etc., it can be used without forming interference / moire with the pixel black matrix of the liquid crystal display device.
[0124]
(Lamination of each layer)
The layers may be stacked only by stacking, but it is preferable that the layers be stacked using an adhesive or a pressure-sensitive adhesive from the viewpoint of workability and light use efficiency. In this case, the adhesive or the pressure-sensitive adhesive is preferably transparent, has no absorption in the visible light range, and has a refractive index as close as possible to the refractive index of each layer from the viewpoint of suppressing surface reflection. From this viewpoint, for example, an acrylic pressure-sensitive adhesive can be preferably used. Each layer separately forms a monodomain in the form of an alignment film, and is sequentially laminated on a light-transmissive substrate by a method such as transfer, or without an adhesive layer or the like. Can be formed as appropriate, and each layer can be directly formed sequentially.
[0125]
Particles may be added to each layer and (adhesive) adhesive layer to adjust the degree of diffusion, if necessary, to impart isotropic scattering, an ultraviolet absorber, an antioxidant, and leveling during film formation. A surfactant or the like can be appropriately added for the purpose of imparting properties.
[0126]
(Other materials)
The liquid crystal display device is manufactured by appropriately using various optical layers and the like according to a conventional method.
[0127]
Polarizing plates (PL) are arranged on both sides of the liquid crystal cell. The polarizing plates (PL) arranged on both sides of the liquid crystal cell are arranged such that their polarization axes are substantially orthogonal to each other. The polarizing plate (PL) on the incident side is arranged so that the direction of the polarization axis thereof is aligned with the axis direction of linearly polarized light obtained by transmission from the light source side.
[0128]
Generally, a polarizing plate having a protective film on one or both sides of a polarizer is generally used.
[0129]
The polarizer is not particularly limited, and various types can be used. Examples of the polarizer include a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymer-based partially saponified film, and a dichromatic dye such as iodine or a dichroic dye. And uniaxially stretched by adsorbing a hydrophilic substance, or a polyene-based oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride. Among these, a polarizer composed of a polyvinyl alcohol-based film and a dichroic substance such as iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.
[0130]
A polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine and uniaxially stretching can be produced, for example, by dyeing polyvinyl alcohol by immersing it in an aqueous solution of iodine, and stretching the film to 3 to 7 times its original length. If necessary, it can be immersed in an aqueous solution of potassium iodide or the like which may contain boric acid, zinc sulfate, zinc chloride or the like. Further, if necessary, the polyvinyl alcohol-based film may be immersed in water and washed with water before dyeing. By washing the polyvinyl alcohol-based film with water, dirt on the surface of the polyvinyl alcohol-based film and an anti-blocking agent can be washed off. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be stretched and then dyed with iodine. Stretching can be performed in an aqueous solution of boric acid or potassium iodide or in a water bath.
[0131]
As a material for forming the transparent protective film provided on one or both surfaces of the polarizer, a material having excellent transparency, mechanical strength, heat stability, moisture shielding property, isotropy and the like is preferable. For example, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, and styrene such as polystyrene and acrylonitrile / styrene copolymer (AS resin). Polymers, polycarbonate polymers and the like. In addition, polyethylene, polypropylene, polyolefin having a cyclo- or norbornene structure, polyolefin-based polymers such as ethylene-propylene copolymer, vinyl chloride-based polymers, amide-based polymers such as nylon and aromatic polyamide, imide-based polymers, and sulfone-based polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Blends of polymers and the like are also examples of polymers forming the transparent protective film. The transparent protective film can also be formed as a cured layer of a thermosetting resin or an ultraviolet curing resin such as an acrylic, urethane, acrylic urethane, epoxy or silicone resin.
[0132]
Further, polymer films described in JP-A-2001-343529 (WO 01/37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a thermoplastic resin having a side chain And / or an unsubstituted phenyl and a resin composition containing a thermoplastic resin having a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film composed of a mixed extruded product of a resin composition or the like can be used.
[0133]
Although the thickness of the protective film can be determined as appropriate, it is generally about 1 to 500 μm from the viewpoint of workability such as strength and handleability, thinness, and the like. In particular, it is preferably from 1 to 300 µm, more preferably from 5 to 200 µm.
[0134]
Further, it is preferable that the protective film has as little coloring as possible. Therefore, Rth = [(nx + ny) / 2−nz] · d (where nx and ny are the main refractive indices in the film plane, nz is the refractive index in the film thickness direction, and d is the film thickness). A protective film having a retardation value in the film thickness direction of -90 nm to +75 nm is preferably used. By using a film having a retardation value (Rth) in the thickness direction of -90 nm to +75 nm, coloring (optical coloring) of the polarizing plate caused by the protective film can be substantially eliminated. The thickness direction retardation value (Rth) is more preferably -80 nm to +60 nm, and particularly preferably -70 nm to +45 nm.
[0135]
As the protective film, a cellulosic polymer such as triacetyl cellulose is preferable from the viewpoints of polarization characteristics and durability. Particularly, a triacetyl cellulose film is preferable. In the case where protective films are provided on both sides of the polarizer, a protective film made of the same polymer material may be used on both sides thereof, or a protective film made of a different polymer material may be used. Usually, the polarizer and the protective film are in close contact with each other via a water-based adhesive or the like. Examples of the aqueous adhesive include an isocyanate adhesive, a polyvinyl alcohol adhesive, a gelatin adhesive, a vinyl latex, an aqueous polyurethane, and an aqueous polyester.
[0136]
The surface of the transparent protective film on which the polarizer is not adhered may be subjected to a hard coat layer, an antireflection treatment, a treatment for preventing sticking, and a treatment for diffusion or antiglare.
[0137]
The hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate, for example, by applying a suitable ultraviolet-curable resin such as an acrylic resin or a silicone resin to a cured film having excellent hardness and sliding properties, etc., as a transparent protective film. It can be formed by a method of adding to the surface of. The anti-reflection treatment is performed for the purpose of preventing the reflection of external light on the polarizing plate surface, and can be achieved by forming an anti-reflection film or the like according to the related art. In addition, the anti-sticking treatment is performed for the purpose of preventing adhesion to an adjacent layer.
[0138]
The anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate, and is, for example, a roughening method using a sand blast method or an embossing method. The transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a method of mixing transparent fine particles or the like. As the fine particles to be contained in the formation of the surface fine uneven structure, for example, a conductive material composed of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide and the like having an average particle size of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles that may be used and organic fine particles made of a crosslinked or uncrosslinked polymer or the like are used. When forming the fine surface unevenness structure, the amount of the fine particles to be used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, per 100 parts by weight of the transparent resin forming the fine surface unevenness structure. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle expanding function) for diffusing light transmitted through the polarizing plate to increase the viewing angle or the like.
[0139]
The anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer and the like can be provided on the transparent protective film itself, or can be separately provided as an optical layer separately from the transparent protective film.
[0140]
Further, the retardation plate is laminated on a polarizing plate as a viewing angle compensation film and used as a wide viewing angle polarizing plate. The viewing angle compensation film is a film for widening the viewing angle so that an image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed not in a direction perpendicular to the screen but in a slightly oblique direction.
[0141]
As such a viewing angle compensating retardation film, a biaxially stretched film, a bidirectionally stretched film such as a biaxially stretched film such as an obliquely oriented film, and the like, which are subjected to a biaxial stretching process or a stretching process in two orthogonal directions, are used. Examples of the obliquely oriented film include a film obtained by bonding a heat shrinkable film to a polymer film and subjecting the polymer film to a stretching treatment and / or shrinkage treatment under the action of the shrinkage force caused by heating, and a film obtained by obliquely aligning a liquid crystal polymer. No. The viewing angle compensation film can be appropriately combined for the purpose of preventing coloring or the like due to a change in the viewing angle based on the phase difference due to the liquid crystal cell, expanding the viewing angle for good visibility, and the like.
[0142]
In addition, because of achieving a wide viewing angle with good visibility, the optically-compensated retardation, in which an optically anisotropic layer consisting of an alignment layer of liquid crystal polymer, particularly a tilted alignment layer of discotic liquid crystal polymer, is supported by a triacetyl cellulose film A plate can be preferably used.
[0143]
In addition to the above, the optical layer to be laminated in practical use is not particularly limited. For example, one or two or more optical layers which may be used for forming a liquid crystal display device such as a reflection plate or a semi-transmission plate are used. Can be. In particular, a reflective polarizing plate or a transflective polarizing plate obtained by further laminating a reflecting plate or a transflective reflecting plate on an elliptically polarizing plate or a circular polarizing plate is exemplified.
[0144]
The reflection type polarizing plate is provided with a reflection layer on a polarizing plate, and is used to form a liquid crystal display device of a type that reflects incident light from a viewing side (display side) and displays the reflected light. There is an advantage that the built-in light source can be omitted, and the liquid crystal display device can be easily made thinner. The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is provided on one surface of the polarizing plate via a transparent protective layer or the like as necessary.
[0145]
Specific examples of the reflective polarizing plate include a protective film that has been subjected to a mat treatment as required, and a reflective layer formed by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum on one surface. Further, there may be mentioned, for example, those in which fine particles are contained in the protective film to form a fine surface uneven structure, and a reflective layer having the fine uneven structure is provided thereon. The reflective layer having the above-mentioned fine uneven structure has an advantage of diffusing incident light by irregular reflection, preventing directivity and glare, and suppressing unevenness in brightness and darkness. Further, the protective film containing fine particles also has an advantage that the incident light and the reflected light are diffused when transmitting the light, and the unevenness of light and darkness can be further suppressed. The reflective layer of the fine uneven structure reflecting the surface fine uneven structure of the protective film is formed by, for example, protecting the metal transparently by an appropriate method such as an evaporation method such as a vacuum evaporation method, an ion plating method, and a sputtering method, and a plating method. It can be performed by a method of directly attaching to the surface of the layer.
[0146]
The reflection plate can be used as a reflection sheet or the like in which a reflection layer is provided on an appropriate film according to the transparent film instead of the method of directly applying the reflection film to the protective film of the polarizing plate. In addition, since the reflective layer is usually made of a metal, the use form in which the reflective surface is covered with a protective film, a polarizing plate, or the like is used to prevent a decrease in reflectance due to oxidation, and as a result, a long-lasting initial reflectance. It is more preferable to avoid separately providing a protective layer.
[0147]
The transflective polarizing plate can be obtained by forming a transflective reflective layer such as a half mirror that reflects and transmits light with the reflective layer. A transflective polarizing plate is usually provided on the back side of a liquid crystal cell. When a liquid crystal display device or the like is used in a relatively bright atmosphere, an image is displayed by reflecting incident light from the viewing side (display side). In a relatively dark atmosphere, a liquid crystal display device of a type that displays an image using a built-in light source such as a backlight built in the back side of a transflective polarizing plate can be formed. That is, the transflective polarizing plate can save energy for use of a light source such as a backlight in a bright atmosphere, and is useful for forming a liquid crystal display device of a type that can be used with a built-in light source even in a relatively dark atmosphere. It is.
[0148]
Further, the polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers as in the above-mentioned polarized light separating type polarizing plate. Therefore, a reflective elliptically polarizing plate or a transflective elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate, semi-transmissive polarizing plate, and retardation plate may be used.
[0149]
The polarizing plate and the retardation plate and the like can be formed by sequentially and separately laminating in the manufacturing process of the liquid crystal display device. There is an advantage that the manufacturing efficiency of a liquid crystal display device or the like can be improved due to its excellent stability and laminating workability.
[0150]
The optical element of the present invention may be provided with an adhesive layer or an adhesive layer. The adhesive layer can be used for sticking to a liquid crystal cell, and also used for laminating an optical layer. At the time of bonding the optical films, their optical axes can be arranged at an appropriate angle depending on the intended retardation characteristics and the like.
[0151]
The adhesive and the pressure-sensitive adhesive are not particularly limited. For example, acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate / vinyl chloride copolymer, modified polyolefin, epoxy polymer, fluorine polymer, rubber polymer such as natural rubber, synthetic rubber, etc. Can be appropriately selected and used. In particular, those having excellent optical transparency, exhibiting appropriate wettability, cohesiveness, and adhesive properties and exhibiting excellent weather resistance and heat resistance can be preferably used.
[0152]
The adhesive or pressure-sensitive adhesive may contain a crosslinking agent according to the base polymer. Adhesives include, for example, natural and synthetic resins, especially tackifying resins, fillers and pigments made of glass fibers, glass beads, metal powders, and other inorganic powders, coloring agents, and antioxidants. An additive such as an agent may be contained. An adhesive layer containing fine particles and exhibiting light diffusivity may be used.
[0153]
The adhesive or pressure-sensitive adhesive is usually used as an adhesive solution having a solid content concentration of about 10 to 50% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent. As the solvent, an organic solvent such as toluene or ethyl acetate or a solvent corresponding to the kind of the adhesive such as water can be appropriately selected and used.
[0154]
The pressure-sensitive adhesive layer or the adhesive layer may be provided on one side or both sides of a polarizing plate or an optical film as a superposed layer of different compositions or types. The thickness of the pressure-sensitive adhesive layer can be appropriately determined depending on the purpose of use, adhesive strength, and the like, and is generally 1 to 500 µm, preferably 5 to 200 µm, particularly preferably 10 to 100 µm.
[0155]
Until practical use, a separator is temporarily attached to the exposed surface of the adhesive layer or the like for the purpose of preventing contamination, and covered. This can prevent the adhesive layer from coming into contact with the adhesive layer in a normal handling state. Except for the above thickness conditions, the separator may be, for example, a plastic film, a rubber sheet, paper, cloth, a nonwoven fabric, a net, a foamed sheet or a metal foil, a suitable thin sheet such as a laminate thereof, or a silicone-based material as necessary. Appropriate conventional ones, such as those coated with an appropriate release agent such as long mirror alkyl, fluorine or molybdenum sulfide, can be used.
[0156]
In the present invention, the optical element and the like, and each layer such as an adhesive layer, for example, a salicylic acid ester compound or a benzophenol compound, a benzotriazole compound or a cyanoacrylate compound, an ultraviolet absorber such as a nickel complex salt compound. It may be one having an ultraviolet absorbing ability by a method such as a treatment method.
[0157]
【Example】
Hereinafter, the present invention will be described with reference to examples, but the present invention is described below and is not limited to the examples.
[0158]
In addition, the front phase difference is such that the direction in which the in-plane refractive index is maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the film is the Z axis, and the refractive index in each axial direction is nx. As ny and nz, the refractive index nx, ny and nz at 550 nm were measured with an automatic birefringence measuring device (manufactured by Oji Scientific Instruments, automatic birefringence meter KOBRA21ADH), and the thickness d (nm) of the retardation layer. From this, the front phase difference: (nx−ny) × d and the phase difference in the thickness direction: (nx−nz) × d were calculated. The phase difference measured when tilted can be measured by the automatic birefringence measuring device. The tilt phase difference is (nx−ny) × d when tilted.
[0159]
The Nz coefficient is defined by the formula: Nz = (nx−nz) / (nx−ny).
[0160]
The reflection wavelength band was a reflection wavelength band having a reflectance of half of the maximum reflectance by measuring a reflection spectrum with a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., instantaneous multiphotometry system MCPD-2000).
[0161]
Example 1
(Production of secondary light-collecting element (Y))
TiO as the secondary light-collecting element (Y) ₂ / SiO ₂ A deposited multilayer bandpass filter having 15 layers was used. As the substrate, a polyethylene terephthalate film having a thickness of 50 μm was used, and the overall thickness was about 53 μm. Table 1 below shows a design drawing of the laminated thickness of the deposited thin film.
[0162]
[Table 1]

[0163]
(light source)
9. Backlight (manufactured by Stanley Electric Co., Ltd.) using a sidelight type light guide (the light guide has a wedge-shaped cross section and dot printing is performed on the back side) as the bright line light source (L) A 4-inch type was used. A three-wavelength cold cathode tube was used as a light source.
[0164]
(Wavelength characteristics)
The wavelength characteristics of the cold-cathode tube as the light source and the vapor-deposited multilayer band-pass filter as the secondary light-collecting element (Y) are as shown in FIG. The measurement of the wavelength characteristics was performed by using a spectrophotometer U4100 manufactured by Hitachi, Ltd.
[0165]
(Light collection characteristics of secondary light collection element (Y))
The graph shown in FIG. 23 is obtained by measuring the light-collecting characteristics of the structure shown in FIG. 15 using only the vapor-deposited multilayer band-pass filter as the secondary light-collecting element (Y).
[0166]
In the graph shown in FIG. 23, a secondary peak is seen around 70 °. This is because the vapor-deposited multilayer film band-pass filter (Y) shifts blue due to oblique incidence, the transmission region for green light shows transmission for blue light, and the transmission region for red light shows transmission for green light. For this reason, strong coloring of the emitted light from oblique directions was recognized. Further, since the emitted light distribution of the used backlight system emits a strong light beam at an angle of ± 60 ° or more from the front, coloring is conspicuous.
[0167]
(Backlight system having primary condensing part (X))
A prism sheet was used as the primary condensing section (X). As the prism sheet, two 3M BEF films (about 180 μm thick, made of polyethylene terephthalate film, apex angle of about 90 °, prism pitch of 50 μm) were used.
[0168]
Two sheets were laminated on the light guide of the bright line light source (L) so that the prism ridges of the prism sheet were arranged orthogonally. A backlight system (BLS) having a prism sheet as such a primary light condensing part (X) has a characteristic of condensing light within ± 50 ° with respect to the front direction.
[0169]
(Condensing system)
A backlight system (BLS) having the primary light-collecting portion (X) and a secondary light-collecting element (Y) are arranged in the structure shown in FIG. FIG. 24 shows the results of measuring the light-collecting characteristics in the structure shown in FIG. As a liquid crystal cell (LC), a 10.4 inch TFT cell manufactured by Sharp Corporation was used. As a polarizing plate (PL), SEG1465DU manufactured by Nitto Denko Corporation was used and bonded to both sides of a liquid crystal cell (LC) so as to be orthogonal. The secondary light-collecting element (Y) was bonded to a polarizing plate (PL). In the following examples, the same liquid crystal cell (LC) and the same polarizing plate (PL) were used.
[0170]
From FIG. 24, it can be seen that the primary condensing dramatically reduces the transmission component at a large angle of the collimated film, and can remove unpleasant coloring. It can be seen that, due to the effect of the primary condensing part (X), the light emitted from the backlight is narrowed down to about ± 50 °, so that the secondary transmission near 70 ° is cut and does not occur.
[0171]
Example 2
(Production of secondary light-collecting element (Y))
As the secondary light-collecting element (Y), a cholesteric liquid crystal band-pass filter produced by applying a cholesteric liquid crystal polymer thin film was used. This is a combination of a three-wavelength band-pass filter that reflects right circularly polarized light and a three-wavelength band-pass filter that reflects left circularly polarized light. Light rays are reflective.
[0172]
In the cholesteric liquid crystal bandpass filter, the transmitted light in the front is unpolarized light. This is because the liquid crystal layer is used as a bandpass filter, and transmitted light from a region where polarization separation by cholesteric reflection is not performed is transmitted in the front direction. Therefore, in measuring the light-collecting characteristics, the secondary light-collecting element (Y) and the polarizing plate (PL) were stacked without providing a retardation layer.
[0173]
Specifically, the selective reflection circularly polarized light band that reflects right circularly polarized light has a selective reflection wavelength range of 440 nm to 490 nm, 550 to 600 nm, and 615 to 700 nm with respect to the emission spectrum of 435 nm, 545 nm, and 610 nm of the three-wavelength cold cathode tube. A pass filter was prepared. As the liquid crystal material used, three kinds of cholesteric liquid crystal polymers having selective reflection central wavelengths of 480 nm, 570 nm, and 655 nm were produced based on European Patent Application Publication No. 0834754.
[0174]
The cholesteric liquid crystal polymer has the following formula 1:
Embedded image

And a polymerizable nematic liquid crystal monomer A represented by the following formula 2:
Embedded image

Was prepared by polymerizing a liquid crystal mixture in which the polymerizable chiral agent B represented by the following formula (1) was blended in the ratio (weight ratio) shown in Table 2 below. Each of the liquid crystal mixtures was made into a 33% by weight solution dissolved in tetrahydrofuran, and then purged with nitrogen in an environment of 60 ° C., and a reaction initiator (azobisisobutyronitrile, 0.5% by weight based on the mixture) ) Was added to carry out a polymerization treatment. The obtained polymer was purified by reprecipitation separation with diethyl ether. Table 2 shows the selective reflection wavelength band.
[0175]
[Table 2]

[0176]
The cholesteric liquid crystal polymer was dissolved in methylene chloride to prepare a 10% by weight solution. The solution was coated on an alignment substrate with a wire bar so that the thickness when dried was about 1 μm. A 75 μm-thick polyethylene terephthalate film was used as an alignment base material, and a polyvinyl alcohol layer was formed on the surface of the polyethylene terephthalate film at a thickness of about 0.1 μm. One coated with 1 μm and rubbed with a rubbing cloth made of rayon was used. After coating, it was dried at 140 ° C. for 15 minutes. After the completion of the heat treatment, the liquid crystal was cooled and fixed at room temperature to obtain a thin film.
[0177]
Using each of the above cholesteric liquid crystal polymers, a liquid crystal thin film of each color was produced through the same steps as described above, and then bonded together with an isocyanate-based adhesive. Thereafter, the polyethylene terephthalate substrate was removed, and three liquid crystal layers were laminated in order from the short wavelength side to obtain a liquid crystal composite layer having a thickness of about 5 μm.
[0178]
On the other hand, three layers of liquid crystal layers are laminated in the same manner as described above except that the polymerizable chiral agent B is an enantiomer instead of chemical formula 2, and selectively reflects left circularly polarized light. A circularly polarized bandpass filter was manufactured.
[0179]
The two liquid crystal surfaces are bonded to each other with a translucent acrylic adhesive (Nitto Denko No. 7, 25 μm thick), and then the polyethylene terephthalate film of the supporting substrate is peeled off to remove the cholesteric liquid crystal band pass filter ( (About 35 μm thick).
[0180]
(Wavelength characteristics)
The wavelength characteristics of the cholesteric liquid crystal bandpass filter as the secondary light condensing element (Y) are as shown in FIG. The graph shown in FIG. 21 is obtained by measuring the light-collecting characteristics of the structure shown in FIG. 15 using the cholesteric liquid crystal band-pass filter as the secondary light-collecting element (Y) alone.
[0181]
(Backlight system having primary condensing part (X))
As in Example 1, a backlight system (BLS) in which two prism sheets were stacked was used as the primary light-collecting unit (X).
[0182]
(Condensing system)
A backlight system (BLS) having the primary light-collecting portion (X) and a secondary light-collecting element (Y) are arranged in the structure shown in FIG. FIG. 26 shows the results of measuring the light-collecting characteristics in the structure shown in FIG.
[0183]
From FIG. 26, it can be seen that the primary condensing dramatically reduces the transmission component of the collimated film at a large angle, thereby removing unpleasant coloring. It can be seen that, due to the effect of the primary condensing part (X), the light emitted from the backlight is narrowed down to about ± 50 °, so that the secondary transmission near 70 ° is cut and does not occur.
[0184]
Example 3
(Production of secondary light-collecting element (Y))
As the secondary light-collecting element (Y), a polarizing element in which a retardation plate (b1) was provided between two circularly-polarizing reflective polarizers (a1) in which the wavelength bands of polarized light selective reflection overlap each other was used.
[0185]
A cholesteric liquid crystal layer of a NIPOCS film (PCF400) manufactured by Nitto Denko Corporation was used as the circular polarization type reflective polarizer (a1).
[0186]
Next, a retardation layer (b1: negative C plate) having a front retardation of approximately 0 and generating a retardation in an oblique direction was prepared from a polymerizable liquid crystal by the following method. LC242 manufactured by BASF was used as the polymerizable mesogen compound, and LC756 manufactured by BASF was used as the polymerizable chiral agent. The polymerizable mesogen compound and the polymerizable chiral agent are mixed at a mixing ratio (weight ratio) of polymerizable mesogen compound / polymerizable chiral agent of 11/88 such that the selective reflection center wavelength of the obtained cholesteric liquid crystal becomes about 350 nm. did. The selective reflection center wavelength of the obtained cholesteric liquid crystal was 350 nm.
[0187]
The specific production method is as follows. A polymerizable chiral agent and a polymerizable mesogen compound are dissolved in cyclopentane (30% by weight) to prepare a solution to which a reaction initiator (Irgacure 907 manufactured by Ciba Specialty Chemicals, 1% by weight based on the mixture) is added. did. In the solution, a surfactant BYK-361 (manufactured by Big Chem Japan) was added to the mixture at a concentration of 0.1%. 01% by weight was added. As an alignment substrate, a polyethylene terephthalate film manufactured by Toray: Lumirror (thickness: 75 μm) which was subjected to an alignment treatment with a rubbing cloth was used.
[0188]
The solution was applied with a wire bar at a coating thickness of 7 μm when dried, dried at 90 ° C. for 2 minutes, heated once to an isotropic transition temperature of 130 ° C., and then gradually cooled. While maintaining a uniform alignment state, the composition was cured by ultraviolet irradiation (10 mW / square cm × 1 minute) in an environment of 80 ° C. to obtain a negative C plate (b1). When the phase difference of the negative C plate (b1) was measured, the phase difference was about 190 nm (> λ / 8) when the light having a wavelength of 550 nm was inclined by 2 nm in the front direction and 30 °.
[0189]
A negative C plate (b1) was adhered to the upper part of the circularly polarizing reflective polarizer (a1) obtained above using a translucent acrylic pressure-sensitive adhesive (Nitto Denko Corporation, No. 7, 25 μm thick). Thereafter, the substrate was peeled off. On top of this, a circular polarization type reflective polarizer (a1) was further laminated and transferred to obtain a polarizing element. The polarizing element was used as a secondary light-collecting element (Y).
[0190]
Since the secondary light condensing element (Y) of the third embodiment has a polarization separation function over the entire visible light band, the front transmitted light is circularly polarized by the polarization separation function of the cholesteric liquid crystal. Therefore, a 波長 wavelength plate (B) is provided between the polarizing plate (PL) on the backlight side of the liquid crystal cell (LC) and the secondary light-collecting element (Y) with respect to the polarization axis of the polarizing plate (PL). It was inserted at an inclination of 45 ° and bonded with a translucent acrylic adhesive (Nitto Denko No. 7, 25 μm). This is for converting the circularly polarized light into linearly polarized light to enhance the transmission characteristics to the polarizing plate.
[0191]
(Backlight system having primary condensing part (X))
A prism sheet was used as the primary condensing section (X). As the prism sheet, two 3M BEF films (about 180 μm thick, made of polyethylene terephthalate film, apex angle of about 90 °, prism pitch of 50 μm) were used.
[0192]
Two sheets were laminated on a dot printed acrylic light guide plate (side light type backlight made by Chatani Sangyo) so that the prism ridge lines of the prism sheet were arranged orthogonally. A backlight system having a prism sheet as such a primary condensing section (X) has a characteristic of condensing light within ± 55 °.
[0193]
(Light collection characteristics of secondary light collection element (Y))
The graph shown in FIG. 27 is obtained by measuring the light-collecting characteristics using the polarizing element (A) as the secondary light-collecting element (Y) in the structure of FIG. 17 alone. In the graph shown in FIG. 27, a leaked light beam is observed outside of 50 ° or more.
[0194]
(Condensing system)
A backlight system (BLS) having the primary light-collecting portion (X) and a secondary light-collecting element (Y) are arranged in the structure shown in FIG. FIG. 28 shows the result of measuring the light condensing characteristics in the structure of FIG. 27 and 28 were measured by Ez-Contrast manufactured by ELDIM.
[0195]
From FIG. 28, it can be recognized that the primary light condensing dramatically reduces the transmission component of the collimated film at a large angle, thereby removing unpleasant coloring. The primary light condensing portion (X) reduces rays emitted from the light source at an angle of 50 ° or more, eliminates light passing through the secondary light condensing element (Y), and leaves only the central secondary light converging portion. That is, only the front looks bright, and the oblique direction is jet black and no coloring is visible.
[0196]
Example 4
(Production of secondary light-collecting element (Y))
As a secondary light-collecting element (Y), a phase difference plate (b1) is provided between two linear polarization type reflection polarizers (a2) where wavelength bands of polarized light selective reflection overlap each other. On both sides of b1), a polarizing element having a layer (b2) having a front phase difference of approximately λ / 4 was used.
[0197]
As the linear polarization type reflection polarizer (a2), 3M DBEF was used. The retardation plate (b1) was produced according to the method for producing a negative C plate in Example 3. The obtained negative C plate (b1) was measured to have a thickness of 8 μm and a phase difference of 0 nm in the front direction with respect to light having a wavelength of 550 nm. )Met. A Nitto Denko NRF film (front retardation: 140 nm) was used as a retardation plate (b2) for sandwiching the negative C plate, and the respective axes and 45 ° ( (−45 °), and five sheets were laminated. The laminate was bonded with a translucent acrylic adhesive (No. 7, manufactured by Nitto Denko, 25 μm thick).
[0198]
(Backlight system having primary condensing part (X))
As a backlight system (BLS) having a primary condensing portion (X), a cross-section wedge-type acrylic light guide / sidelight-type backlight having a microprism array formed on the surface (taken from an IBM notebook PC ThinkPad) was used. . The backlight system (BLS) having the primary condensing part (X) condenses the light emitted from the light source primary within ± 50 ° with respect to the front direction.
[0199]
(Light collection characteristics of secondary light collection element (Y))
The graph shown in FIG. 29 is obtained by measuring the light condensing characteristics of the polarizing element (A) alone as the secondary light condensing element (Y) in the structure of FIG. In the graph shown in FIG. 29, a leaked light beam is observed outside ± 50 ° or more with respect to the front direction. In the structure of FIG. 19, a light box (direct backlight, diffused light source) made by Hakuba was used as the light source (L).
[0200]
(Condensing system)
A backlight system (BLS) having the primary light-collecting portion (X) and a secondary light-collecting element (Y) are arranged in the structure shown in FIG. FIG. 30 shows the results obtained by measuring the light-collecting characteristics using the structure shown in FIG.
[0201]
From FIG. 30, it is recognized that the primary condensing dramatically reduces the transmission component of the collimated film at a large angle, thereby removing unpleasant coloring.
[0202]
Comparative example
The cholesteric liquid crystal bandpass filter of Example 2 was used as a light-condensing film. It was placed on a dot printed light guide plate. The light-collecting characteristics are as shown in FIG. 2, and a strong peak of secondary transmission is observed.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an example of a basic principle of making a polarizing element (A) parallel light.
FIG. 2 illustrates the state of each light beam shown in FIGS. 1, 3, 4, 6, and 8.
FIG. 3 is a conceptual diagram illustrating conversion of linearly polarized light into circularly polarized light.
FIG. 4 is a conceptual diagram showing an example of a basic principle of making a polarizing element (A) parallel light.
FIG. 5 is an example showing an arrangement angle of each layer for parallel light conversion using a linear polarization type reflection polarizing element (a2).
FIG. 6 is a conceptual diagram showing an example of a basic principle of parallel light conversion of a polarizing element (A).
FIG. 7 is an example showing an arrangement angle of each layer for parallel light conversion using a linear polarization type reflection polarizing element (a2).
FIG. 8 is a conceptual diagram showing an example of the basic principle of making the polarizing element (A) parallel light.
FIG. 9 is an example showing an arrangement angle of each layer for parallel light conversion using a linear polarization type reflection polarizing element (a2).
FIG. 10 is a conceptual diagram showing a direct solution of moiré.
FIG. 11 is an example of a schematic diagram of a light collection system of the present invention.
FIG. 12 is an example of a schematic diagram of a light collection system of the present invention.
FIG. 13 is an example of a schematic view of a transmission type liquid crystal display device of the present invention.
FIG. 14 is an example of a schematic view of a transmission type liquid crystal display device of the present invention.
FIG. 15 is a schematic diagram of a transmissive liquid crystal display device when the light condensing characteristics of the secondary light condensing element (Y) alone are measured in Examples 1 and 2.
FIG. 16 is a schematic view of a transmission type liquid crystal display device of Examples 1 and 2.
FIG. 17 is a schematic diagram of a transmissive liquid crystal display device when the light-collecting characteristics of the secondary light-collecting element (Y) alone are measured in Example 3.
FIG. 18 is a schematic view of a transmission type liquid crystal display device according to a third embodiment.
FIG. 19 is a schematic diagram of a transmissive liquid crystal display device when the light-collecting characteristics of the secondary light-collecting element (Y) alone are measured in Example 4.
FIG. 20 is a schematic diagram of a transmission type liquid crystal display device of Example 4.
FIG. 21 is a graph illustrating light-collecting characteristics of the secondary light-collecting element (Y) of Example 2 alone.
FIG. 22 is a graph showing a wavelength characteristic of the secondary light-collecting element (Y) of Example 1.
FIG. 23 is a graph showing light-collecting characteristics of the secondary light-collecting element (Y) of Example 1 alone.
FIG. 24 is a graph showing light collecting characteristics when a backlight system having a primary light collecting section (X) and a secondary light collecting element (Y) are combined in Example 1.
FIG. 25 is a graph showing a wavelength characteristic of the secondary light-collecting element (Y) of Example 2.
FIG. 26 is a graph showing light collecting characteristics when a backlight system having a primary light collecting section (X) and a secondary light collecting element (Y) are combined in Example 2.
FIG. 27 is a graph showing a wavelength characteristic of the secondary light-collecting element (Y) of Example 3.
FIG. 28 is a graph showing light collecting characteristics when a backlight system having a primary light collecting section (X) and a secondary light collecting element (Y) are combined in Example 3.
FIG. 29 is a graph showing a wavelength characteristic of the secondary light-collecting element (Y) of Example 4.
FIG. 30 is a graph showing the light-collecting characteristics when a backlight system having a primary light-collecting portion (X) and a secondary light-collecting element (Y) in Example 4 are combined.
[Explanation of symbols]
X Primary focusing unit
Y secondary focusing element
L light source
BLS backlight system
a1 Circularly polarized reflective polarizer
a2 Linear polarization type reflective polarizer
b retardation layer
A Polarizing element
B λ / 4 plate
LC liquid crystal cell
PL polarizing plate

Claims (16)

A backlight system having a light source and a primary light collector (X) capable of collecting light emitted from the light source within ± 60 ° with respect to the front direction;
A light-collecting system comprising a light-collecting film having no pattern structure as a secondary light-collecting element (Y). The light collection system according to claim 1, wherein the backlight system having the primary light collection part (X) is a light source and a microprism sheet array arranged on the light source. The light collection system according to claim 1, wherein the backlight system having the primary light collection part (X) is a microprism processing light guide combined with a light source. The light collection system according to claim 1, wherein the backlight system having the primary light collection part (X) is a microdot processing light guide combined with a light source. Since the light-condensing film used as the secondary light-condensing element (Y) does not have a pattern structure, when the light-condensing film is applied to a liquid crystal cell and optically observed from the surface side (viewing side), The light collecting system according to any one of claims 1 to 4, wherein a moiré or interference fringe does not occur with the regular pattern of the optical member. A light-condensing film used as a secondary light-condensing element (Y) has a retardation layer (b) disposed between at least two reflective polarizers (a) in which the wavelength bands of polarized light selective reflection overlap each other. The light-collecting system according to any one of claims 1 to 5, wherein the polarizing element (A) is provided. The reflective polarizer (a) is a circularly polarized reflective polarizer (a1) that transmits certain circularly polarized light and selectively reflects opposite circularly polarized light,
The phase difference layer (b) has a front phase difference (normal direction) of substantially zero, and a phase difference layer (b1) of λ / 8 or more with respect to incident light incident at an angle of 30 ° or more with respect to the normal direction. 7. The light collection system according to claim 6, comprising: The reflection polarizer (a) is a linear polarization type reflection polarizer (a2) that transmits one of orthogonal linearly polarized lights and selectively reflects the other, and
The phase difference layer (b) has a front phase difference (normal direction) of substantially zero, and a phase difference layer (b1) of λ / 4 or more with respect to incident light incident at an angle of 30 ° or more with respect to the normal direction. Have
On both sides of the phase difference layer (b1), a layer (b2) having a front phase difference of approximately λ / 4 is provided between the layer and the linear polarization type reflective polarizer (a2);
The incident side layer (b2) is at an angle of 45 ° (−45 °) ± 5 ° with respect to the polarization axis of the incident side linear polarization type reflective polarizer (a2).
The emission-side layer (b2) has an angle of −45 ° (+ 45 °) ± 5 ° with respect to the polarization axis of the emission-side linear polarization type reflective polarizer (a2).
The incident side layer (b2) and the exit side layer (b2) have an arbitrary angle formed by their slow axes,
The light collection system according to claim 6, wherein the light collection system is arranged. The reflection polarizer (a) is a linear polarization type reflection polarizer (a2) that transmits one of orthogonal linearly polarized lights and selectively reflects the other, and
The retardation layer (b) has two biaxial retardation layers (b3) having a front retardation of approximately λ / 4 and an Nz coefficient of 2 or more,
The incident-side layer (b3) has a slow axis direction at an angle of 45 ° (−45 °) ± 5 ° with respect to the polarization axis of the incident-side linear polarization type reflective polarizer (a2).
The emission-side layer (b3) has a slow axis direction at an angle of -45 ° (+ 45 °) ± 5 ° with respect to the polarization axis of the emission-side linearly polarizing reflective polarizer (a2).
The incident side layer (b3) and the exit side layer (b3) have an arbitrary angle formed by their slow axes,
The light collection system according to claim 6, wherein the light collection system is arranged. The reflection polarizer (a) is a linear polarization type reflection polarizer (a2) that transmits one of orthogonal linearly polarized lights and selectively reflects the other, and
The retardation layer (b) has one biaxial retardation layer (b4) having a front retardation of approximately λ / 2 and an Nz coefficient of 1.5 or more,
The slow axis direction of the incident side layer is at an angle of 45 ° (−45 °) ± 5 ° with respect to the polarization axis of the linear polarization type reflective polarizer (a2) on the incident side.
The direction of the slow axis of the emission-side layer is −45 ° (+ 45 °) ± 5 ° with respect to the polarization axis of the emission-side linear polarization type reflective polarizer (a2).
The polarization axes of the two linearly polarizing reflective polarizers (a2) are substantially orthogonal,
The light collection system according to claim 6, wherein the light collection system is arranged. The light-collecting system according to any one of claims 1 to 5, wherein the light-collecting film used as the secondary light-collecting element (Y) is a band-pass filter, and the light source has a bright line spectrum. The light-collecting system according to claim 11, wherein the band-pass filter is a vapor-deposited multilayer band-pass filter. The light-collecting system according to claim 11, wherein the band-pass filter is a cholesteric liquid crystal band-pass filter. The light-collecting system according to claim 11, wherein the band-pass filter is a band-pass filter made of a stretched film of a multilayer laminated extruded substrate of resin materials having different refractive indices. The light-collecting system according to claim 11, wherein the band-pass filter is a band-pass filter made of a multilayer thin film precision coated film of resin materials having different refractive indexes. A light-collecting system according to any one of claims 1 to 15,
A liquid crystal cell through which the collimated light passes,
Polarizing plates arranged on both sides of the liquid crystal cell,
A transmissive liquid crystal display device characterized by containing at least:

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