JP2004004763A - LCD with wide viewing angle - Google Patents

Abstract

An object of the present invention is to provide a liquid crystal display device which is thin and can realize a wide viewing angle.
A polarizing element (A) in which a retardation layer (b) is disposed between at least two reflective polarizers (a) in which wavelength bands of polarized light selective reflection overlap each other, A backlight system that parallelizes the diffused light source, a liquid crystal cell through which the parallelized light passes, polarizers disposed on both sides of the liquid crystal cell, and a transmission panel disposed on the viewing side of the liquid crystal cell A viewing angle-enlarging layer (W) for diffusing the reflected light beam.
[Selection diagram] FIG.

Description

で表される。数１中、Ｓ１：第一格子ピッチ、Ｓ２：第二格子、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。
【００８３】
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り、格子構造を有さない本発明の偏光素子が視野角拡大システムの作製に大きな効果があることが分かる。
【００８４】
さらにプリズムアレイやマイクロレンズシート類と比べ、平行光を発生する薄膜層は反射偏光子を含めても数十〜数百μｍレベルであり、極めて薄型化の設計が容易である。また、空気界面を必要としないので貼り合わせて使用が可能であり、ハンドリング面で大きなアドバンテージが得られる。たとえば、反射偏光子にコレステリック液晶ポリマー（約１０μｍ）を用いた場合、組み合わせる位相差板も液晶ポリマーの塗工薄膜を用い（約５μｍ）、接着剤で積層すれば（約５μｍ）総計５０μｍ以下にまで薄膜化できる。各層を直接塗工し界面無く作製すればさらに薄層化可能である。
【００８５】
【発明の効果】
本発明の視野角拡大液晶表示装置は、コントラストが最も高く色再現性が良好な視野各領域にのみ出射光線を集束する。その結果、液晶表示装置から得られる映像は良好な表示品位の領域のみを明るくすることができる。
【００８６】
厚みも平行光化を発現する機能膜は２００μｍ以下、作製時の支持体基材の厚みを除けば数十μｍ程度で実用上十分な性能の光学膜が得られる。これは、従来のレンズやプリズムなどの幾何光学材料では実現し得なかった厚みである。すなわち、従来から提案されてきた視野角拡大システムと比べて大きなアドバンテージである。
【００８７】
このシステムを用いて正面近傍領域の良好な表示特性の光線を平均化し、角度を広げることで、階調反転や色調変化への耐性が高い、視野角特性良好な液晶表示装置を得ることができる。このシステムでは液晶表示装置のセルは、従来から存在する通常のＴＮ液晶に補償フィルムを用いない場合であっても十分高い特性が得られ、高コストの液晶配行制御や特殊な位相差板を必要としない。
【００８８】
このように本発明の視野角拡大液晶表示装置によれば、従来不可能であった薄型の視野角拡大システムが容易に低コストで実現できる。
【００８９】
【発明の実施の形態】
以下に、本発明の視野角拡大液晶表示装置の概念図の好ましい態様の例示は、図１１〜図１６、図１８に示す通りである。
【００９０】
本発明の偏光素子（Ａ）は、偏光の選択反射の波長帯域が互いに重なっている少なくとも２枚の反射偏光子（ａ）の間に、正面位相差と斜め入射光に対して位相差が前記特異的な値を示す位相差層（ｂ）を配置して重畳することにより形成することができる。
【００９１】
これにより、入射側の反射偏光子を斜め透過した光の一部を出射側の反射偏光子によって全反射させることが可能となる。この効果により、集光・平行光化されるバックライト光源上に配置された液晶表示装置は正面近傍の表示品位の高い領域のみの光線を利用することができ、視認側に配置する視野角拡大のための光拡散手段を用いて良好な表示品位の光線を広げ、視野角拡大システムを形成することができる。
【００９２】
（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。
【００９３】
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。
【００９４】
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。
【００９５】
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。
【００９６】
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。
【００９７】
（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。
【００９８】
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。
【００９９】
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。
【０１００】
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。
【０１０１】
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。
【０１０２】
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。
【０１０３】
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。
【０１０４】
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。
【０１０５】
（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。
【０１０６】
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。
【０１０７】
（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。
【０１０８】
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。
【０１０９】
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。
【０１１０】
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。
【０１１１】
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。
【０１１２】
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。
【０１１３】
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。
【０１１４】
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。
【０１１５】
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。
【０１１６】
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。
【０１１７】
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。
【０１１８】
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。
【０１１９】
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。
【０１２０】
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。
【０１２１】
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。
【０１２２】
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。
【０１２３】
（拡散反射板（Ｆ）の配置）
光源たる導光板（Ｅ）の下側（液晶セルの配置面とは反対側）には拡散反射板（Ｆ）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（Ｆ）の配置が望ましい。
【０１２４】
（拡散板（Ｄ）の配置）
本発明における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（Ｄ）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。
【０１２５】
用いられる拡散板（Ｄ）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（Ｄ）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。
【０１２６】
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（Ｄ）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。
【０１２７】
（視野角拡大層（Ｗ）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。
【０１２８】
ここで用いられる視野角拡大層（Ｗ）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（ＰＬ）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（ＰＬ）〜液晶セル（ＬＣ）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。
【０１２９】
液晶セル（ＬＣ）の視認側の偏光板（ＰＬ）より外側に視野角拡大層（Ｗ）を位置する場合には液晶セル（ＬＣ）−偏光板（ＰＬ）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（Ｗ）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。
【０１３０】
一方で、偏光板（ＰＬ）と液晶セル（ＬＣ）の間に視野角拡大層（Ｗ）を挿入する場合には偏光板（ＰＬ）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（ＰＬ）の視野角特性を補償する位相差板（Ｃ）を偏光板（ＰＬ）と視野角拡大層（Ｗ）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（ＰＬ）の視野角特性を補償する位相差板（Ｃ）を挿入するのが好ましい。
【０１３１】
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（Ｗ）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（Ｗ）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。
【０１３２】
本発明においては視野角拡大層（Ｗ）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。
【０１３３】
（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。
【０１３４】
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。
【０１３５】
本発明における偏光素子（Ａ）は用いる反射偏光子（ａ）と位相差層（ｂ）が前記要件を満たす限り、波長依存性は少なく正面にのみ透過、斜め方向は反射によりカットできる。従来技術の例えば、米国特許出願公開第２００２／３６７３５号明細書に記載されているような干渉フィルターと輝線発光光源の組み合わせによる平行光化・集光システムと比べて光源の特性に対する依存性が少ない特徴を有している。
【０１３６】
（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。
【０１３７】
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。
【０１３８】
偏光板（ＰＬ）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。
【０１３９】
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。
【０１４０】
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。
【０１４１】
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。
【０１４２】
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。
【０１４３】
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。
【０１４４】
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。
【０１４５】
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。
【０１４６】
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。
【０１４７】
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。
【０１４８】
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。
【０１４９】
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。
【０１５０】
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。
【０１５１】
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。
【０１５２】
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。
【０１５３】
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。
【０１５４】
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。
【０１５５】
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。
【０１５６】
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。
【０１５７】
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。
【０１５８】
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。
【０１５９】
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。
【０１６０】
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。
【０１６１】
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。
【０１６２】
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。
【０１６３】
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。
【０１６４】
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。
【０１６５】
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。
【０１６６】
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。
【０１６７】
【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。
【０１６８】
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。
【０１６９】
Ｎｚ係数は、式：Ｎｚ＝（ｎｘ−ｎｚ）／（ｎｘ−ｎｙ）で定義される。
【０１７０】
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。
【０１７１】
その他の、実験に用いた計測器は以下の通りである。
ヘイズ測定は、村上色彩社製のヘイズメーターＨＭ１５０を用いた。
透過反射の分光特性は、日立製作所製の分光光度計Ｕ４１００を用いた。
偏光板の特性は、村上色彩製のＤＯＴ３を用いた。
輝度計測は、トプコン社製の輝度計ＢＭ７を用いた。
紫外線照射は、ウシオ電機社製のＵＶＣ３２１ＡＭ１を用いた。
【０１７２】
実施例１
（円偏光型反射偏光子（ａ１）の作製）
市販の重合性ネマチック液晶モノマーとカイラル剤を用いて作製した。用いたコレステリック液晶は重合性メソゲン化合物と重合性カイラル剤の混合物からなり、重合性メソゲン化合物としてはＢＡＳＦ社製のＬＣ２４２、重合性カイラル剤としてはＢＡＳＦ社製ＬＣ７５６を用いた。
【０１７３】
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５５０ｎｍ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）＝５／９５、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：５４５ｎｍ、選択反射波長帯域幅：約６０ｎｍ、であった。
【０１７４】
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（２０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。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。
【０１７５】
前記溶液をワイヤーバーにて乾燥時塗布厚み５μｍ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）にて硬化して円偏光型反射偏光子（ａ１）を得た。ガラス板に、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、得られた円偏光型反射偏光子（ａ１）を転写した。得られた得られた円偏光型反射偏光子（ａ１）の選択反射波長帯域は約５２０〜５８０ｎｍであった。
【０１７６】
（ネガティブＣプレートの作製）
次いで、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。
【０１７７】
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：３５０ｎｍ、であった。
【０１７８】
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。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。
【０１７９】
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。
【０１８０】
（偏光素子（Ａ）およびそれを利用したバックライトシステムの作製）
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、本発明の偏光素子（Ａ）を得た。本サンプルは、狭帯域で可視光全域をカバーしていないので、単色光源上にて平行光化効果を確認した。
【０１８１】
得られた偏光素子（Ａ）に５４４ｎｍに輝線を有する緑色拡散光源を配置した。この光源には、冷陰極管としてエレバム製Ｇ０型を茶谷工業製ドット印刷サイドライト型バックライト装置内（Ｅ）に配置し、偏光素子（Ａ）との間には光散乱板（Ｄ：きもと製，ヘイズ９０％以上）を配置し、拡散光源として用いた。バックライト下面にはマットＰＥＴに銀蒸着を行った拡散反射板（Ｆ）を配置した。
【０１８２】
この拡散光源上に配置した偏光素子（Ａ）は法線方向には光線が出射されるが、斜め２０°程度より急激に透過光線が減少し始め、斜め３０°程度で半減し、斜め４５°前後では出射光線がほとんど無くなることが確認できた。
【０１８３】
（視野角拡大液晶表示装置の作製）
次に、この偏光素子（Ａ）を用いた単色光源バックライトに、市販のＴＮ液晶セル（ＬＣ）を配置した。ＴＮ液晶は視野角補正の為の位相差フィルムを有さない東芝製ＴＦＴ液晶セルを用いた（対角１０．　４インチ）。ただし、上下の偏光板（ＰＬ）は日東電工社製のＳＥＧ１４２５ＤＵに貼り替えて用いた。
【０１８４】
先に作製した集光バックライト上に、位相差層（Ｂ）として、λ／４板（日東電工社製のＮＲＦフィルム，正面位相差１４０ｎｍ）を配置した。その位相差層（Ｂ）の遅相軸角度に対して、液晶セル下面の偏光板（ＰＬ）の偏光軸方向が４５°の角度となるように配置し、正面透過光量が最大となる位置で透光性アクリル系粘着剤（日東電工社製，ＮＯ．７，２５μｍ厚）にて、液晶セル（ＬＣ）背面〜偏光板（ＰＬ）〜λ／４板（Ｂ）〜偏光素子（Ａ）を各々貼り合わせた。
【０１８５】
さらに視野角拡大層（Ｗ）として透光性アクリル粘着剤（日東電工社製　ＮＯ．７　屈折率＝１．　４７）中にシリカ真球状粒子（粒径４μｍ　配合部数３０ｗｔ％　屈折率１．　４４）を分散したヘイズ９２％の光拡散粘着層を作製した。厚みは約３０μｍであった。これを液晶表示装置表面側の偏光板（ＰＬ）と液晶セル（ＬＣ）の間に貼り合わた。
【０１８６】
得られた視野角拡大液晶表示装置は図１１に示す通りである。当該視野角拡大液晶表示装置は、法線方向に対して傾斜角±６０°以内にて階調反転が生じず、グレースケール表示による視野角特性において良好な表示特性を維持した。視野角拡大層（Ｗ）が偏光板（ＰＬ）と液晶セル（ＬＣ）間に挿入されているため、液晶セル（ＬＣ）を垂直透過した光線は液晶の視野角特性の影響は受けないが偏光板（ＰＬ）の視野角特性の影響は若干受けた。しかし、本発明における平行光化光源と視野角拡大層（Ｗ）の組み合わせを用いない、従来型の液晶表示装置と比べれば特性は向上していた。
【０１８７】
実施例２
（ポジティブＣプレートの作製）
正面位相差０、斜め方向で位相差を発生する位相差層（ｂ１：ポジティブＣプレート）を重合性液晶にて作製した。重合性液晶化合物としては、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を用いた。
【０１８８】
具体的な製法は、以下の通りである。重合性ネマチック液晶モノマーＡ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，前記モノマーＡに対して１重量％）を添加した溶液を調製した。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）に、離型処理剤（オクタデシルトリメトキシシラン）のシクロヘキサン溶液（０．　１重量％）を、塗布、乾燥して形成したものを垂直配向膜として用いた。
【０１８９】
前記重合性ネマチック液晶モノマーＡ溶液を、ワイヤーバーにて乾燥時塗布厚みが２．　５μｍ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）にて硬化してポジティブＣプレート（ｂ１）を得た。このポジティブ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は正面方向では０ｎｍ、３０°傾斜させて測定したときの位相差は約２００ｎｍ（＞λ／８）であった。
【０１９０】
（偏光素子（Ａ）の作製）
実施例１において、ネガティブＣプレート（ｂ１）の代わりに、上記ポジティブＣプレート（ｂ１）を用いたこと以外は実施例１に準じて偏光素子（Ａ）を得た。
【０１９１】
（視野角拡大液晶表示装置の作製）
得られた偏光素子（Ａ）を用いて、実施例１と同じ液晶表示装置・光源装置を用いて、視野角拡大システムを組み立てた。ただし、視野角拡大層（Ｗ）である拡散粘着層は、液晶表示装置の上板偏光板（ＰＬ）の上に貼り合わせ、その上にアンチグレア処理付きトリアセチルセルロースフィルム（ＡＧ：日東電工社製，ＡＧＳ１付き８０μｍＴＡＣ）を貼り合わせた。得られた視野角拡大液晶表示装置は図１２に示す通りである。特性は、実施例１とおおよそ同等の性能であった。実施例２では視野角拡大層（Ｗ）が偏光板（ＰＬ）上に配置されたので実施例１と比べて偏光板（ＰＬ）の視野角特性の影響は受けなかったが、外光（日光や照明などの入射光）の後方散乱が生じ、若干コントラストが低下した。しかし、従来型の液晶表示装置より視野角特性は優れていた。
【０１９２】
実施例３
（直線偏光型反射偏光子（ａ２）の作製）
ポリエチレンナフタレート（ＰＥＮ）／ナフタレンジカルボン酸−テレフタル酸コポリエステル（ｃｏ−　ＰＥＮ）が交互に積層するよう、薄膜をフィードブロック法にて交互に厚み制御して、２０層積層した多層膜を得た。この多層膜を一軸延伸した。延伸温度は約１４０℃として、延伸倍率はＴＤ方向に約３倍とした。得られた延伸フィルム中の各薄層の厚みは概略０．　１μｍ程度であった。得られた２０層積層フィルム延伸品をさらに５枚積層し、計１００枚積層品として、直線偏光型反射偏光子（ａ２）を得た。直線偏光型反射偏光子（ａ２）は、５００ｎｍ以上６００ｎｍ以下の波長帯域にて直線偏光に対して反射機能を有していた。
【０１９３】
（偏光素子（Ａ）の作製）
実施例１で得られたネガティブＣプレート（ｂ１）の両側に、位相差層（ｂ２）として、ポリカーボネート製の一軸延伸フィルムからなるλ／４板（日東電工社製，ＮＲＦフィルム，正面位相差１３５ｎｍ）を配置した。さらに、その外側に、図５の軸配置になるように直線偏光型反射偏光子（ａ２）を配置して、偏光素子（Ａ）を得た。すなわち、上記で得られた直線偏光型反射偏光子（ａ２）を、入射側の直線偏光型反射偏光子（ａ２）の透過偏光軸を０°とした場合に、λ／４板（ｂ２）：４５°、Ｃプレート（ｂ１：軸方位無し）、λ／４板（ｂ２）：−４５°、出射側の直線偏光型反射偏光子（ａ２）の透過軸９０°となるように配置した。これら各層は透光性のアクリル系粘着材（日東電工社製Ｎｏ．７　２５μｍ厚）で積層した。実施例１と同様にネガティブＣプレート（ｂ１）の基材は除去して用いた。
【０１９４】
（視野角拡大液晶表示装置の作製）
得られた偏光素子（Ａ）を用いて、実施例１と同じ液晶表示装置・光源装置を用いて、視野角拡大システムを組み立てた。さらに偏光板（ＰＬ）と視野角拡大層（Ｗ）間に、位相差層（Ｃ）として、偏光板視野角補償位相差板（富士写真フィルム製，８０μｍＴＡＣの２軸延伸位相差板）を挿入した。これは、液晶セル（ＬＣ）を垂直近傍で透過した光線は、視野角拡大層（Ｗ）で拡散した後に偏光板（ＰＬ）に入射するため、液晶セル（ＬＣ）の視角特性は現れないが、偏光板（ＰＬ）が持つ視野角特性は現れてしまうことを抑制するためのものである。なお、偏光板（ＰＬ）と偏光素子（Ａ）との間には、λ／４板（Ｂ）は配置しなかった。
【０１９５】
得られた視野角拡大液晶表示装置は図１３に示す通りである。特性は実施例１とおおよそ同等の性能で、偏光板の軸方向（画面正面から見て斜め±４５°方向）での偏光板そのものの視野角不足領域での特性が向上した。
【０１９６】
実施例４
（偏光素子（Ａ）の作製）
透過偏光軸が互いに直交配置した２層の実施例３で得られた直線偏光型反射偏光子（ａ２）の間に、位相差層（ｂ４）として、ポリカーボネート製フィルムを２軸延伸して得られた位相差フィルム（正面位相差２７０ｎｍ、Ｎｚ係数＝１．　５）を図９に準じて貼り合わせて偏光素子（Ａ）を作製した。当該位相差フィルムは鐘淵化学工業社製の無延伸ポリカーボネートフィルムを２軸延伸機にて延伸配向して作製した。各層の貼り合わせは透光性アクリル粘着材（日東電工社製，ＮＯ．７，２５μｍ厚）を用いた。
【０１９７】
（視野角拡大液晶表示装置の作製）
得られた偏光素子（Ａ）を用いて、実施例１と同様にしてバックライトシステムを作製した。
【０１９８】
次に、この偏光素子（Ａ）を用いた単色光源バックライトに、液晶セル（ＬＣ）としてカラーＳＴＮ液晶（１０．　４インチ）を配置した。上下の偏光板（ＰＬ）は日東電工社製のＳＥＧ１４２５ＤＵに貼り替えて用いた。また、液晶セル（ＬＣ）と偏光板（ＰＬ）との間には、位相差層（Ｃ）として、ＳＴＮ補償位相差板（日東電工社製のＮＲＦフィルム、正面位相差４３０ｎｍ，ポリカーボネート製、厚み５０μｍ，粘着剤層厚み２５μｍ）を挿入した。視野角拡大層（Ｗ）としては表面形状によるマイクロレンズアレイシート（ヘイズ９０％相当、レンズピッチ約２０μｍ）を偏光板（ＰＬ）表面側に配置した。これらは、透光性アクリル系粘着剤（日東電工社製，ＮＯ．７，２５μｍ厚）にて各々貼り合わせた。
【０１９９】
得られた視野角拡大液晶表示装置は図１４に示す通りである。当該視野角拡大液晶表示装置は、基本となった液晶表示装置の正面最大コントラストが約２０程度と低いものの、実施例１と同様に階調反転は見られず、実用的な視野角範囲は広い物が得られた。
【０２００】
実施例５
（円偏光型反射偏光子（ａ１）の作製）
選択反射中心波長の異なる４層のコレステリック液晶ポリマーと溶媒を含有する塗工液を、予めポリイミド配向膜を設けてラビング処理したトリアセチルセルロースフィルムのラビング処理面に塗布し、広帯域の円偏光型反射偏光子（ａ１）を得た。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４６０ｎｍ、５１０ｎｍ、５８０ｎｍ、６６０ｎｍとなる４種のコレステリック液晶ポリマーを作製した。
【０２０１】
コレステリック液晶ポリマーは、下記化２：
【化２】

で表される重合性ネマチック液晶モノマーＡと、下記化３：
【化３】

で表される重合性カイラル剤Ｂを、下記表１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１に示す。
【０２０２】
【表１】

【０２０３】
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１．　５μｍになるようワイヤーバーで塗工した。配向基材として、８０μｍ厚のトリアセチルセルロースフィルム（富士写真フイルム工業製，ＴＤ−ＴＡＣ）を用い、その表面にポリイミド層を約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。
【０２０４】
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、透明イソシアネート系接着材ＡＤ２４４（特殊色料工業製）にて貼り合わせた。Ｒ色とＧ色の液晶薄膜面同士を貼り合わせ、Ｇ側のトリアセチルセルロース基材を剥離した。同様にしてＢ色をＧ色液晶薄膜面に貼り合わせた後、Ｒ側のトリアセチルセルロース基材を剥離した。これにより、各液晶層を短波長側から順に４層を積層した約１０μｍ厚のコレステリック液晶複合層を得た。得られたコレステリック液晶複合層からなる円偏光型反射偏光子（ａ１）は４３０ｎｍ〜７１０ｎｍで選択反射機能を有した。
【０２０５】
（偏光素子（Ａ）およびそれを利用したバックライトシステムの作製）
上記得られた円偏光型反射偏光子（ａ１）を、実施例１で作製したネガティブＣプレート（ｂ１）の両側に透光性粘着材（日東電工社製，Ｎｏ．７，２５μｍ厚）で貼り合わせて偏光素子（Ａ）を作製した。上下の円偏光型反射偏光子（ａ１）は、円偏光の方向が同じものを用いた。
【０２０６】
得られた偏光素子（Ａ）を、３波長に輝線を有する冷陰極管（４３５ｎｍ、５４５ｎｍ、６１０ｎｍ）を用いた多摩電気工業製の直下型バックライト（Ｄ）に配置した。この場合も法線方向には光線が出射されるが、斜め２０°以上では透過光線が急激に減少し、３０°近傍では半減、４５°近傍では正面輝度に対して１０％程度まで低下した。偏光素子（Ａ）が可視光全域に対応しているため可視光全域で正面のみ透過し、斜め方向には透過しない集光素子として機能した。
【０２０７】
（視野角拡大液晶表示装置の作製）
得られたバックライトシステムを用いて、実施例２と同じ、液晶セル（ＬＣ）と視野角拡大層（Ｗ）の積層品と同等の構成品を重ね合わせ、視野角拡大液晶表示装置を得た。得られた視野角拡大液晶表示装置は図１５に示す通りである。
【０２０８】
実施例６
（偏光素子（Ａ）およびそれを利用したバックライトシステムの作製）
直線偏光型反射偏光子（ａ２）として、３Ｍ社製のＤＢＥＦを用いた。当該直線偏光型反射偏光子（ａ２）に対し、位相差層（ｂ３）として、ポリカーボネート製フィルムを２軸延伸して得られた位相差フィルム（正面位相差１４０ｎｍ、Ｎｚ係数＝２）を図６、７に準じて貼り合わせて偏光素子（Ａ）を作製した。当該位相差フィルムは鐘淵化学工業社製の無延伸ポリカーボネートフィルムを２軸延伸機にて延伸配向して作製した。各層の貼り合わせは透光性アクリル粘着材（日東電工社製，ＮＯ．７，２５μｍ厚）を用いた。
【０２０９】
光源装置として３波長に輝線を有する冷陰極管（４３５ｎｍ、５４５ｎｍ、６１０ｎｍ）を用いたサイドライト型バックライト（Ｅ：スタンレー電気製）に光拡散板（Ｄ：きもと製，ヘイズ約９０％）配置し、それに偏光素子（Ａ）を配置した。バックライト下面にはマットＰＥＴに銀蒸着を行った拡散反射板（Ｆ）を配置した。
【０２１０】
（視野角拡大液晶表示装置の作製）
得られたバックライトシステムを用いて、図１６に示す視野角拡大液晶表示装置を作製した。液晶セル（ＬＣ）として、東芝製のカラーＴＦＴ液晶（１０．　４インチ）を用いた。視野角拡大層（Ｗ）としては表面形状によるマイクロレンズアレイシートを用いた。偏光板（ＰＬ）は日東電工社製のＳＥＧ１４２５ＤＵを用いた。
【０２１１】
上記マイクロレンズアレイシートはヘイズ９０相当である。レンズピッチは約２０μｍであり、真鍮製金型研削品より転写形成して作製したものである。基材フィルムは富士写真工業社製の５０μｍクリアーＴＡＣである。形状転写樹脂は紫外線重合エポキシ樹脂（旭電化工業社製，ＫＲ４１０）にて、金型表面にシリコン樹脂にて離型処理後、エポキシ樹脂を滴下した。ガラス棒を用いエポキシ樹脂を全面に一様に広げた後、基材フィルムを貼り合わせ、紫外線重合（１０ｍＷ３０秒間）にて形成した形状をフィルム上に転写した。これを図１６の上側偏光板（ＰＬ）の表面に対し、基材フィルムを偏光板（ＰＬ）側へ、凹凸転写面を空気に面する側に配置し、貼り合わせた。得られた視野角拡大液晶表示装置は正面より±６０°で階調反転が見られなかった。
【０２１２】
本システムでは視野角拡大マイクロレンズアレイと液晶表示装置のブラックマトリクスが干渉し、モアレが生じたがマイクロレンズアレイの貼り合わせ角度を４５°傾斜させることでモアレを緩和することができた。またこの際に偏光反射子からなる偏光素子との干渉は生じなかった。
【０２１３】
実施例７
（偏光素子（Ａ）の作製）
直線偏光型反射偏光子（ａ２）として、３Ｍ社製のＤＢＥＦを用いた。実施例１で得られたネガティブＣプレート（ｂ１）の両側に、位相差層（ｂ２）として、ポリカーボネート製の一軸延伸フィルムを２層異軸で積層して成る広帯域λ／４位相差板（日東電工社製のＮＲＦフィルム，正面位相差１４０ｎｍと、同ＮＲＺフィルム，正面位相差２７０ｎｍ，Ｎｚ係数＝０．　５の積層物）を配置した。広帯域λ／４位相差板（ｂ２）の積層軸関係は図１７に示す。これは、直線偏光型反射偏光子（ａ２）が可視光全域をカバーする広帯域なものなので、集光・平行光化の波長特性を揃え、斜め方向での入射光線を反射する際に波長による反射率の差を押さえるためである。これにより、斜め方向で出射光線が減光する際に色による減光率の差が小さくなり、色調の変動が少なく光線を絞り込める。
【０２１４】
さらに、その外側に、図５の軸配置になるように直線偏光型反射偏光子（ａ２）を配置して、偏光素子（Ａ）を得た。すなわち、直線偏光型反射偏光子（ａ２）を、入射側の直線偏光型反射偏光子（ａ２）の透過偏光軸を０°としてた場合に、λ／４板（ｂ２）：４５°、Ｃプレート（ｂ１：軸方位無し）、λ／４板（ｂ２）：−４５°、出射側の直線偏光型反射偏光子（ａ２）の透過軸９０°となるように配置した。これら各層は透光性のアクリル系粘着材（日東電工社製のＮｏ．７，２５μｍ厚）で積層した。実施例１と同様にネガティブＣプレート（ｂ１）の基材は除去して用いた。
【０２１５】
（視野角拡大液晶表示装置の作製）
得られた偏光素子（Ａ）を用いて、実施例１と同様の視野角拡大システムを組み立てた。得られた視野角拡大液晶表示装置は図１８に示す通りである。ただし、視野角拡大層（Ｗ）としてホログラム拡散板を配置した。また、バックライトは３波長型（４３５ｎｍ、５４５ｎｍ、６１０ｎｍ）の冷陰極管を用いたスタンレー電気製サイドライト型バックライト（Ｅ）を用いた。拡散板（ヘイズ約９０）を組み合わせた物を用いた。また液晶セル（ＬＣ）はシャープ製ＴＦＴ液晶セル（１１．　３インチ）を用いた。
【０２１６】
特性は実施例１とおおよそ同等の性能であった。偏光板の軸方向（画面正面から見て斜め±４５°方向）での偏光板そのものの視野角不足領域での特性が向上した。
【０２１７】
比較例１
実施例１〜７の視野角拡大液晶表示装置から、反射偏光子（ａ）と位相差板（ｂ）から成る偏光素子（Ａ）を削除した。いずれの液晶表示装置も、視野角拡大層（Ｗ）の拡散効果により視野角特性は平均化されるが、階調反転する領域の光線も含めて平均化されるので、黒表示の輝度が向上して、コントラストが低下した。
【０２１８】
さらに階調反転した領域である法線方向から傾斜角±４５°以上の領域では平均化しても階調反転した映像の平均しか得られない。そのため、視野角拡大層（Ｗ）の効果は見られず、階調反転が生じ、グレースケール表示にて不自然な明暗変化が認められた。
【０２１９】
比較例２
実施例６において、偏光素子（Ａ）の代わりに、３Ｍ社製のライトコントロールフィルムを用いて平行光源を得た。しかし、マイクロレンズアレイと液晶表示装置の画素のブラックマトリクスと干渉が生じモアレが視認された。そこでマイクロレンズアレイを回転させて軽減を試みたが、マイクロレンズアレイを回転させるとライトコントロールフィルムのピッチとの間でモアレを生じ、両者消去することができなかった。
【０２２０】
比較例３
実施例３において、直線偏光型反射偏光子（ａ２）の代わりに、市販のヨウ素系吸収２色性偏光子（日東電工社製，ＮＰＦ−ＥＧ１４２５ＤＵ）を用いたこと以外は、実施例３と同様な組み合わせで偏光素子を作製した。当該偏光素子を用いて、実施例１と同様の視野角拡大液晶表示装置の作製した。しかし正面方向の透過特性と斜め方向の吸収特性による視野角制限効果は得られるが吸収損失が著しく、正面の明るさは向上せず、著しく暗い表示しか得られなかった。
【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、図３、図４、図６、図８の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】実施例１の視野角拡大液晶表示装置の概念図である。
【図１２】実施例２の視野角拡大液晶表示装置の概念図である。
【図１３】実施例３の視野角拡大液晶表示装置の概念図である。
【図１４】実施例４の視野角拡大液晶表示装置の概念図である。
【図１５】実施例５の視野角拡大液晶表示装置の概念図である。
【図１６】実施例６の視野角拡大液晶表示装置の概念図である。
【図１７】実施例７における二層異軸の広帯域λ／４位相差板（ｂ２）の積層軸関係を示す概念図である。
【図１８】実施例７の視野角拡大液晶表示装置の概念図である。
【符号の説明】
ａ　　反射偏光子
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
Ｃ　　補償位相差層
Ｄ　　拡散板
Ｅ　　サイドライト型導光板または直下型バックライト
Ｆ　　拡散反射板
ＡＧ　アンチグレア層
ＬＣ　液晶セル
ＰＬ　偏光板
Ｗ　　視野角拡大層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a viewing angle widening liquid crystal display device.
[0002]
[Prior art]
As a system for expanding the viewing angle of a liquid crystal display device, the backlight is made parallel to take out only rays with good contrast and color tone near the front, and by diffusing them, the light near the front at any angle can be seen. There is known a method of obtaining a display of the same quality as that of Japanese Patent Application Laid-Open (JP-A) Nos. 2000-187, and (see, for example, Patent Documents 1 and 2).
[0003]
However, it is difficult for this type of liquid crystal display device to have a backlight technology for obtaining parallel light. For example, the systems proposed in Patent Literature 1 and Patent Literature 2 have many problems in practical use because the backlight system is thick, the light use efficiency is low, and the cost is high.
[0004]
In a TN type liquid crystal display device that does not use a normal viewing angle compensation film, the region where high contrast is obtained is only about ± 20 ° from the front. In the case of STN liquid crystal, it is limited to a narrower range. To extract only light rays with good display quality near the front,
1) A method of narrowing the parallelism of the light emitted from the backlight to about ± 20 ° at a half-value width, and widening the transmitted light in the vicinity of the front by diffusing means after passing through the liquid crystal cell to enlarge the viewing angle.
2) a method of extracting only light rays in the vicinity of the front of ± 20 ° from the light rays transmitted through the liquid crystal display device, and spreading the light rays by a diffusing means;
There are two types.
[0005]
However, the method 2) has a large light loss and is not suitable for liquid crystal display applications. Further, in the 1) method, when a prism light condensing sheet represented by 3M BEF or the like is used for the backlight, the parallelism is limited to about ± 40 °. The collimation of light due to the shape of the backlight light guide was also limited to about ± 40 °, and the capability was insufficient for use in a system for expanding the viewing angle of a liquid crystal display device.
[0006]
[Patent Document 1]
JP-A-10-333147
[Patent Document 2]
JP-A-10-25528
[0007]
[Problems to be solved by the invention]
As the parallel light converting means, there is a method using a light shielding louver represented by a light control film manufactured by 3M Company or the like. However, in the above method, the parallel light conversion has a large absorption loss and has a problem in brightness. That is, one of the thickness, the brightness, and the parallelism of the obtained light has to be sacrificed due to a design problem, and there are many practical problems. In particular, for use in notebook PCs and mobile phones, the increase in the thickness of the parallel light optical system is desirably 200 μm or less, and more desirably 100 μm or less. It is desired that the maximum thickness increase be 500 μm or less even in the case of assembling, but it has been difficult to realize the above method.
[0008]
On the other hand, parallelizing means using a mirror, a lens, a prism, or a light guide is known. However, according to this method, the thickness and weight are remarkably increased, and it is not an effective means except for a special use such as a projector.
[0009]
Therefore, in the viewing angle liquid crystal display device, the light is narrowed down to about ± 20 ° within the range where the good viewing angle characteristics of the liquid crystal display device can be obtained, while the thin film-like structure is used to make the light parallel, and the light is absorbed further. It was necessary to reduce losses.
[0010]
Further, with the parallel light converting means using a light shielding louver, a micro lens array, a prism, or the like, moire occurs between the fine structure and the pixel of the liquid crystal display device, and it is difficult to obtain a good display. Since no light is emitted from the joints of the prisms, the gaps between the lenses, and the like, the emitted light has in-plane shading regularly, which causes moire. Although it is possible to insert a diffusion means for preventing moiré, there is a problem that the parallelism of the obtained parallel light is deteriorated, which causes a practical problem.
[0011]
In some cases, even if the interference between the liquid crystal pixel and the parallel light converting means was reduced by changing the period of the regularity, it further interfered with the fine structure of the parallel light diffusing means arranged on the display surface side of the liquid crystal display device. When a structure having regularity such as a microlens array or microprisms is used for the parallel light diffusing means, interference with the fine structure occurs.
[0012]
Therefore, in order to prevent interference with the liquid crystal pixels, it is necessary to devise the size of the fine structure and the arrangement method of the parallel light diffusion means. However, since the design for preventing the interference with the liquid crystal pixels is the same as the means for preventing the interference with the liquid crystal pixels of the collimating means, the problem that the members that have escaped the interference cause interference again easily occurs.
[0013]
For example, if the size of the structure that does not interfere with the liquid crystal pixels is adopted for the parallel light converting means, the size of the structure that does not interfere with the liquid crystal pixels is also used for the parallel light diffusing means, so that the size of the parallel light diffusing means is exactly the size of interference. The same applies to the angle and arrangement, etc., and the allowable design range was narrow, and the selectable optical system range was extremely narrow.
[0014]
As described above, the viewing angle widening system including the parallel light converting means and the parallel light diffusing means has narrow design options due to optical problems caused by the respective fine structures, and has been difficult to be put into practical use.
[0015]
In addition to the type that requires a large depth and air interface using the surface structure of lenses, mirrors and prisms and refraction and reflection, and the front light condensing / parallel light system that has a large absorption loss like a light shielding louver, Conventionally, studies have been made to convert a light source into parallel light using a special optical film.
[0016]
As a typical method, there is a method performed by a combination of a bright line light source and a band pass filter. For example, Philips, JP-A-6-235900, JP-A-2-158289, JP-T10-510671, U.S. Pat. No. 6,307,604, German Patent No. 3836955, German Patent Application Publication No. 422028, European Patent Application Publication No. 578302, US Patent Application Publication No. 2002/34009, and Japanese Patent Publication No. 02/25687.
[0017]
In addition, a band-pass filter is arranged on a light source / display device that emits a bright line such as a CRT or electroluminescence as disclosed in U.S. Patent Application Publication No. 2001 / 521,643 and U.S. Patent Application Publication No. 2001/516066. There is a method.
[0018]
Also, as described in US Patent Application Publication No. 2002/36735 of Fuji Photo Film Industry Co., Ltd., and JP-A-2002-90535 and JP-A-2002-258048 of Nitto Denko Corporation, a bright line type cold cathode tube is used. A method of arranging a band-pass filter corresponding to three wavelengths.
[0019]
However, these techniques will not work unless the light source has a bright line spectrum. Therefore, there is a problem relating to the design and manufacture of a film that selectively functions for a specific wavelength. Further, when the bandpass filter is a deposition interference film, there is also a problem of reliability such that the wavelength characteristic changes due to a change in the refractive index of the thin film in a humid environment.
[0020]
On the other hand, an example of a parallel light conversion system using a hologram-based material is described in US Pat. No. 4,984,872 by Rockwell. However, although this kind of material has a high frontal transmittance, it cannot completely reflect and remove obliquely incident light. When parallel light is incident and the direct transmittance is calculated, the transmittance is measured high because the front direction passes straight, while the transmittance is measured low by scattering the oblique incident light, but on the diffuse light source No difference is made. Therefore, when it is arranged on an actual diffused backlight light source, the light condensing function cannot be sufficiently performed. Moreover, many hologram-based materials have weak physical properties, and there are many problems in reliability.
[0021]
An object of the present invention is to provide a liquid crystal display device which is thin and can realize a wide viewing angle.
[0022]
[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 viewing angle widening liquid crystal display device, and have completed the present invention. That is, the present invention is as follows.
[0023]
1. Using a polarizing element (A) in which a retardation layer (b) is arranged between at least two reflective polarizers (a) in which the wavelength bands of polarized light selective reflection overlap each other, a parallel light source of a diffuse light source is used. A backlight system that has been lightened,
A liquid crystal cell through which the collimated light passes,
Polarizing plates arranged on both sides of the liquid crystal cell,
A viewing angle expansion layer disposed on the viewing side of the liquid crystal cell for diffusing transmitted light,
A viewing angle widening liquid crystal display device characterized by containing at least
[0024]
2. 2. The viewing angle widening liquid crystal display device according to the above item 1, wherein the selective reflection wavelengths of at least two reflective polarizers (a) overlap each other in a wavelength range of 550 nm ± 10 nm.
[0025]
3. The reflective polarizer (a) is a circularly polarized reflective polarizer (a1) that transmits certain circularly polarized light and selectively reflects opposite circularly polarized light,
A phase difference layer (b1) having a front phase difference (normal direction) of substantially zero and a phase difference of λ / 8 or more with respect to incident light that is incident at an angle of 30 ° or more with respect to the normal direction (b1); 3. The viewing angle widening liquid crystal display device according to the above item 1 or 2, comprising:
[0026]
4. 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
A phase difference layer (b1) having a front phase difference (normal direction) of substantially zero and a phase difference of λ / 4 or more with respect to incident light inclined at an angle of 30 ° or more with respect to the normal direction; )
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,
3. The viewing angle widening liquid crystal display device according to the above 1 or 2, wherein the liquid crystal display device is arranged.
[0027]
5. 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,
3. The viewing angle widening liquid crystal display device according to the above 1 or 2, wherein the liquid crystal display device is arranged.
[0028]
6. 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,
3. The viewing angle widening liquid crystal display device according to the above 1 or 2, wherein the liquid crystal display device is arranged.
[0029]
7. 5. The viewing angle widening liquid crystal according to any one of the above items 1 to 4, wherein the retardation layer (b1) is formed by fixing the planar orientation of a cholesteric liquid crystal phase having a selective reflection wavelength range other than the visible light range. Display device.
[0030]
8. 5. The viewing angle widening liquid crystal display device according to any one of the above items 1 to 4, wherein the retardation layer (b1) is one in which the homeotropic alignment state of the rod-shaped liquid crystal is fixed.
[0031]
9. 5. The viewing angle widening liquid crystal display device according to any one of the above items 1 to 4, wherein the retardation layer (b1) is a layer in which a nematic phase or a columnar phase alignment state of the discotic liquid crystal is fixed.
[0032]
10. 5. The viewing angle widening liquid crystal display device according to any one of the above items 1 to 4, wherein the retardation layer (b1) is formed by biaxially orienting a polymer film.
[0033]
11. The retardation layer (b1) is a layer in which an inorganic layered compound having a negative uniaxial property is oriented and fixed so that an optical axis is in a direction normal to a surface, and the retardation layer (b1) is any one of the above items 1 to 4. A viewing angle widening liquid crystal display device as described in the above.
[0034]
12. 12. The viewing angle widening liquid crystal display device according to any one of the above items 3, 6 to 11, wherein a cholesteric liquid crystal is used as the circularly polarizing reflective polarizer (a1).
[0035]
13. A λ / 4 plate is arranged on the viewing side (liquid crystal cell side) of the circular polarization type reflective polarizer (a1), and the axial direction of the linearly polarized light obtained by transmission and the transmission through the lower surface side (light source side) of the liquid crystal display device. 13. The viewing angle widening liquid crystal display device according to any one of the above items 3, 6 to 12, wherein the liquid crystal display device is arranged so that the axial directions are aligned.
[0036]
14． 12. The viewing angle expansion according to any one of 4 to 11, wherein a stretched product of a multilayer laminated film material of a resin material having different refractive index and retardation value is used as the linear polarization type reflection polarizer (a2). Liquid crystal display.
[0037]
15. Wherein the axial direction of the linearly polarized light obtained by transmission of the linearly polarized reflective polarizer (a2) is aligned with the transmission axis direction of the polarizing plate on the lower surface side (light source side) of the liquid crystal display device. 15. The viewing angle widening liquid crystal display device according to 4 to 11 or 14.
[0038]
16. 16. The viewing angle widening liquid crystal display device according to any one of the above 1 to 15, wherein a diffusion plate having substantially no backscattering and no depolarization is used as the viewing angle widening layer.
[0039]
17. 17. The viewing angle widening liquid crystal display device according to any one of the above items 1 to 16, wherein each layer is laminated using a translucent adhesive or a pressure-sensitive adhesive.
[0040]
(Action)
As described in Japanese Patent No. 2,561,483 and Japanese Patent Application Laid-Open No. 10-321,025, a retardation plate controlled so that the phase difference value in the vertical incidence direction and the phase difference value in the oblique incidence direction are specifically different. Is inserted between polarizers, the angular distribution of transmitted light is restricted, and if an absorbing polarizer is used, light is transmitted only near the front and all peripheral light is absorbed. On the other hand, if a reflective polarizer is used as a polarizer, light rays are transmitted only in the vicinity of the front, and all peripheral light rays are reflected. By using such a theory, it is possible to condense and collimate the light emitted from the backlight without causing absorption loss.
[0041]
The present invention will be described below with reference to an ideal model for the mechanism of simultaneously exhibiting the light-collecting property and the brightness enhancement.
[0042]
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.
[0043]
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.
[0044]
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.
[0045]
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.
[0046]
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.
[0047]
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.
[0048]
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.
[0049]
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.
[0050]
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.
[0051]
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).
[0052]
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.
[0053]
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.
[0054]
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.
[0055]
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.
[0056]
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.
[0057]
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.
[0058]
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.
[0059]
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.
[0060]
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.
[0061]
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.
[0062]
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.
[0063]
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.
[0064]
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 ４ wavelength and a Nz coefficient of 2 or more. Things. This is almost the same characteristic as the case of using a three-layer laminate in which a C plate and a retardation layer (b1) are sandwiched between two λ / 4 plates (b2) as shown in FIGS. 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.
[0065]
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.
[0066]
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 °.
[0067]
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.
[0068]
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.
[0069]
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.
[0070]
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 °.
[0071]
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.
[0072]
The polarizing element (A) shown in FIGS. 8 and 9 has one biaxial retardation layer (b4) having a front retardation of about 波長 wavelength and a Nz coefficient of 1.5 or more. It is arranged. This is almost the same characteristic as the case where a three-layer laminate having a structure in which a C plate: a retardation layer (b1) is sandwiched between two λ / 4 plates (b2) as shown in FIGS. 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.
[0073]
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.
[0074]
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 °.
[0075]
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.
[0076]
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.
[0077]
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.
[0078]
As the parallel light diffusing means, a diffusing plate as disclosed in JP-A-2000-347006 and JP-A-2000-347007, which has little backscattering, is suitably used. In this case, the viewing angle is isotropically enlarged, and there is no difference in viewing angle characteristics between up, down, left, and right. A liquid crystal display device having such characteristics is suitably used for DTP applications where the orientation of the liquid crystal display device is changed and the vertical and horizontal directions are often changed, or for digital cameras and video cameras.
[0079]
Also, the use of a diffuser plate with anisotropic light diffusibility and a microlens array sheet with controlled shape anisotropy, such as those found in hologram materials, can selectively improve the viewing angle characteristics in the horizontal and downward directions. It is suitable for use in televisions with landscape screens.
[0080]
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.
[0081]
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.
[0082]
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, S3: the moire fringe pitch, α: the angle between the first grating and the second grating.
[0083]
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 understood that the reduction of the layer having the lattice structure is effective for suppressing the moiré phenomenon, and that the polarizing element of the present invention having no lattice structure has a great effect in manufacturing a viewing angle widening system.
[0084]
Further, as compared with the prism array and the microlens sheets, the thin film layer that generates the parallel light has a level of several tens to several hundreds μm including the reflective polarizer, and it is easy to design a very thin film. In addition, since an air interface is not required, it can be used by bonding together, and a great advantage can be obtained in terms of handling. For example, when a cholesteric liquid crystal polymer (about 10 μm) is used for the reflective polarizer, a combined retardation plate also uses a liquid crystal polymer coated thin film (about 5 μm), and when laminated with an adhesive (about 5 μm), a total of 50 μm or less is obtained. Can be made thinner. If each layer is directly applied and produced without an interface, it can be further thinned.
[0085]
【The invention's effect】
The viewing angle widening liquid crystal display device of the present invention focuses outgoing light rays only in each field of view having the highest contrast and the best color reproducibility. As a result, in the image obtained from the liquid crystal display device, only an area with good display quality can be brightened.
[0086]
The thickness of the functional film exhibiting parallel light is 200 μm or less, and about tens of μm excluding the thickness of the support substrate at the time of production, an optical film having practically sufficient performance can be obtained. This is a thickness that could not be realized with conventional geometric optical materials such as lenses and prisms. That is, this is a great advantage as compared with the viewing angle expansion system that has been conventionally proposed.
[0087]
By averaging light beams having good display characteristics in the vicinity of the front using this system and widening the angle, a liquid crystal display device having high resistance to gradation inversion and color tone and excellent viewing angle characteristics can be obtained. . In this system, the cell of the liquid crystal display device can obtain sufficiently high characteristics even if the compensation film is not used for the conventional TN liquid crystal which has been conventionally used. do not need.
[0088]
As described above, according to the viewing angle widening liquid crystal display device of the present invention, a thin viewing angle widening system that has been impossible in the past can be easily realized at low cost.
[0089]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, examples of preferred embodiments of the conceptual view of the viewing angle widening liquid crystal display device of the present invention are as shown in FIGS. 11 to 16 and 18.
[0090]
The polarizing element (A) of the present invention has a phase difference between the front phase difference and the oblique incident light between at least two reflective polarizers (a) in which the wavelength bands of the polarized light selective reflection overlap each other. It can be formed by arranging and superposing the retardation layers (b) exhibiting specific values.
[0091]
This makes it possible to totally reflect a part of the light obliquely transmitted through the incident-side reflective polarizer by the output-side reflective polarizer. Due to this effect, the liquid crystal display device arranged on the backlight light source that is condensed and collimated can use light rays only in the high display quality area near the front and expand the viewing angle arranged on the viewing side. By using the light diffusing means for (1), light rays of good display quality can be spread, and a viewing angle widening system can be formed.
[0092]
(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.
[0093]
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.
[0094]
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.
[0095]
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.
[0096]
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.
[0097]
(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.
[0098]
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. .
[0099]
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.
[0100]
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.
[0101]
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.
[0102]
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.
[0103]
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.
[0104]
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.
[0105]
(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.
[0106]
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.
[0107]
(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.
[0108]
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.
[0109]
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. .
[0110]
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.
[0111]
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.
[0112]
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.
[0113]
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.
[0114]
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.
[0115]
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
[0116]
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.
[0117]
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.
[0118]
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.
[0119]
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.
[0120]
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.
[0121]
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.
[0122]
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.
[0123]
(Arrangement of diffuse reflection plate (F))
It is desirable to dispose a diffuse reflection plate (F) below the light guide plate (E) as a light source (on the side opposite to the liquid crystal cell arrangement surface). 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 (F) in order to increase the scattered reflection component in the front direction without preserving the reflection angle of the reflected return light beam.
[0124]
(Arrangement of diffusion plate (D))
It is also desirable to provide an appropriate diffusion plate (D) between the collimating film and the backlight light source in the present invention. 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.
[0125]
The diffusion plate (D) to be used can be obtained by a method of embedding fine particles having different refractive indexes in a resin or the like, in addition to the one having the uneven surface shape. This diffusion plate (D) may be sandwiched between the collimating film and the backlight, or may be bonded to the collimating film.
[0126]
When the liquid crystal cell to which the collimating film is attached is arranged close to the backlight, Newton rings may be generated in the gap between the film surface and the backlight, but the light guide plate side surface of the collimating film in the present invention. By disposing a diffusion plate (D) 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.
[0127]
(Arrangement of viewing angle expansion layer (W))
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.
[0128]
As the viewing angle widening layer (W) 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 (PL). However, in order to prevent the influence of pixel bleeding or 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 (PL) and the liquid crystal cell (LC). 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.
[0129]
When the viewing angle widening layer (W) is located outside the polarizing plate (PL) on the viewing side of the liquid crystal cell (LC), the parallel light is transmitted from the liquid crystal cell (LC) to the polarizing plate (PL). Therefore, in the case of a TN liquid crystal cell, it is not particularly necessary to use a viewing angle compensation phase difference 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 (W) has an air surface, it is possible to adopt a type based on a refraction effect due to the surface shape.
[0130]
On the other hand, when the viewing angle widening layer (W) is inserted between the polarizing plate (PL) and the liquid crystal cell (LC), the light is a scattered light at the stage of transmission through the polarizing plate (PL). 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 (C) for compensating the viewing angle characteristics of the polarizing plate (PL) between the polarizing plate (PL) and the viewing angle widening layer (W). In the case of STN liquid crystal, it is preferable to insert a retardation plate (C) for compensating the viewing angle characteristics of the polarizing plate (PL) in addition to the front retardation compensation of the STN liquid crystal.
[0131]
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 emitted light. Therefore, it is not necessary to consider the compatibility with the viewing angle widening layer (W) and the arrangement order. Therefore, the viewing angle widening layer (W) 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.
[0132]
In the present invention, the light as described in JP-A-2000-347006 and JP-A-2000-347007 has substantially no backscattering and does not eliminate polarized light as the viewing angle widening layer (W). A scattering plate having a haze of 80% to 90% is 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.
[0133]
(Lamination of each layer)
The respective layers may be laminated only by stacking, but it is desirable to laminate the respective layers 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.
[0134]
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.
[0135]
As long as the reflective polarizer (a) and the retardation layer (b) to be used satisfy the above requirements, the polarizing element (A) of the present invention has little wavelength dependence and can be transmitted only to the front and cut off in the oblique direction by reflection. There is less dependence on the characteristics of the light source as compared with the prior art, for example, a collimating / light collecting system using a combination of an interference filter and an emission light source as described in US Patent Application Publication No. 2002/36735. Has features.
[0136]
(Other materials)
The liquid crystal display device is manufactured by appropriately using various optical layers and the like according to a conventional method.
[0137]
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.
[0138]
Generally, a polarizing plate (PL) having a protective film on one or both sides of a polarizer is generally used.
[0139]
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.
[0140]
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.
[0141]
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.
[0142]
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.
[0143]
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.
[0144]
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.
[0145]
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.
[0146]
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.
[0147]
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.
[0148]
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.
[0149]
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.
[0150]
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.
[0151]
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.
[0152]
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.
[0153]
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.
[0154]
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.
[0155]
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.
[0156]
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.
[0157]
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.
[0158]
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.
[0159]
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.
[0160]
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.
[0161]
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.
[0162]
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.
[0163]
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.
[0164]
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.
[0165]
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.
[0166]
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.
[0167]
【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.
[0168]
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.
[0169]
The Nz coefficient is defined by the formula: Nz = (nx−nz) / (nx−ny).
[0170]
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).
[0171]
Other measuring instruments used in the experiment are as follows.
The haze was measured using a haze meter HM150 manufactured by Murakami Color Co., Ltd.
The spectrophotometer U4100 manufactured by Hitachi, Ltd. was used for the transmission and reflection spectral characteristics.
The characteristic of the polarizing plate used was DOT3 manufactured by Murakami Color.
The luminance was measured using a luminance meter BM7 manufactured by Topcon Corporation.
For UV irradiation, UVC321AM1 manufactured by Ushio Inc. was used.
[0172]
Example 1
(Production of Circularly Polarized Reflective Polarizer (a1))
It was prepared using a commercially available polymerizable nematic liquid crystal monomer and a chiral agent. The cholesteric liquid crystal used was composed of a mixture of a polymerizable mesogen compound and a polymerizable chiral agent. As the polymerizable mesogen compound, LC242 manufactured by BASF was used, and as the polymerizable chiral agent, LC756 manufactured by BASF was used.
[0173]
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 5/95 such that the obtained cholesteric liquid crystal has a selective reflection center wavelength of about 550 nm. did. The obtained cholesteric liquid crystal had a selective reflection center wavelength of 545 nm and a selective reflection wavelength bandwidth of about 60 nm.
[0174]
The specific production method is as follows. A polymerizable chiral agent and a polymerizable mesogen compound are dissolved in cyclopentane (20% 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. 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.
[0175]
The solution was applied with a wire bar at a coating thickness of 5 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 circularly polarized reflective polarizer (a1). The obtained circularly polarizing reflective polarizer (a1) was transferred to a glass plate using a translucent acrylic pressure-sensitive adhesive (Nitto Denko Corporation, No. 7, 25 μm thickness). The selective reflection wavelength band of the obtained circularly polarizing reflective polarizer (a1) was about 520 to 580 nm.
[0176]
(Preparation of negative C plate)
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. LC242 manufactured by BASF was used as the polymerizable mesogen compound, and LC756 manufactured by BASF was used as the polymerizable chiral agent.
[0177]
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 central wavelength of selective reflection of the obtained cholesteric liquid crystal was 350 nm.
[0178]
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. 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.
[0179]
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 °.
[0180]
(Preparation of Polarizing Element (A) and Backlight System Using It)
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. A circularly polarized reflective polarizer (a1) was further laminated thereon and transferred to obtain a polarizing element (A) of the present invention. Since this sample did not cover the entire visible light region in a narrow band, the collimation effect on a monochromatic light source was confirmed.
[0181]
A green diffusion light source having a bright line at 544 nm was arranged on the obtained polarizing element (A). In this light source, an Elevum G0 type cold cathode tube is disposed in a dot printing sidelight type backlight device (C) manufactured by Chatani Kogyo (E), and a light scattering plate (D: Kimoto) is provided between the light source and the polarizing element (A). And haze 90% or more) were used as a diffusion light source. On the lower surface of the backlight, a diffuse reflection plate (F) in which matte PET was subjected to silver deposition was arranged.
[0182]
The polarizing element (A) disposed on the diffused light source emits light in the normal direction, but the transmitted light starts to decrease sharply from about 20 ° obliquely, halves at about 30 ° oblique, and becomes 45 ° oblique. It was confirmed that there was almost no outgoing light before and after.
[0183]
(Production of liquid crystal display device with expanded viewing angle)
Next, a commercially available TN liquid crystal cell (LC) was arranged in a monochromatic light source backlight using the polarizing element (A). As the TN liquid crystal, a Toshiba TFT liquid crystal cell having no phase difference film for correcting a viewing angle was used (diagonal 10.4 inches). However, the upper and lower polarizing plates (PL) were replaced with SEG1425DU manufactured by Nitto Denko Corporation and used.
[0184]
A λ / 4 plate (NRF film manufactured by Nitto Denko Corporation, front phase difference: 140 nm) was disposed as a retardation layer (B) on the light-collecting backlight previously prepared. The polarizing axis of the polarizing plate (PL) on the lower surface of the liquid crystal cell is arranged at an angle of 45 ° with respect to the slow axis angle of the retardation layer (B). The back of the liquid crystal cell (LC), the polarizing plate (PL), the λ / 4 plate (B), and the polarizing element (A) were coated with a translucent acrylic adhesive (Nitto Denko, No. 7, 25 μm thick). Each was bonded.
[0185]
Furthermore, silica spherical particles (particle size: 4 μm, number of blended parts: 30 wt%, refractive index: 1.44) in a translucent acrylic pressure-sensitive adhesive (Nitto Denko No. 7, refractive index = 1.47) as a viewing angle widening layer (W). Was dispersed to prepare a light diffusion adhesive layer having a haze of 92%. The thickness was about 30 μm. This was bonded between the polarizing plate (PL) on the surface side of the liquid crystal display device and the liquid crystal cell (LC).
[0186]
The obtained viewing angle widening liquid crystal display device is as shown in FIG. The viewing angle widening liquid crystal display device did not cause gradation inversion within an inclination angle of ± 60 ° with respect to the normal direction, and maintained favorable display characteristics in the viewing angle characteristics by gray scale display. Since the viewing angle widening layer (W) is inserted between the polarizing plate (PL) and the liquid crystal cell (LC), the light vertically transmitted through the liquid crystal cell (LC) is not affected by the viewing angle characteristics of the liquid crystal, but is polarized. The viewing angle characteristics of the plate (PL) were slightly affected. However, the characteristics were improved as compared with a conventional liquid crystal display device which does not use the combination of the collimated light source and the viewing angle widening layer (W) in the present invention.
[0187]
Example 2
(Preparation of positive C plate)
A retardation layer (b1: a positive C plate) for generating a retardation in the oblique direction with a front retardation of 0 was prepared from a polymerizable liquid crystal. As the polymerizable liquid crystal compound, the following formula 1:
Embedded image

The polymerizable nematic liquid crystal monomer A represented by the following formula was used.
[0188]
The specific production method is as follows. A polymerizable nematic liquid crystal monomer A was 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 monomer A) was added. The alignment substrate is formed by applying a cyclohexane solution (0.1% by weight) of a release agent (octadecyltrimethoxysilane) to a polyethylene terephthalate film manufactured by Toray: Lumirror (75 μm in thickness) and drying. It was used as a vertical alignment film.
[0189]
The thickness of the polymerizable nematic liquid crystal monomer A solution when dried with a wire bar is 2. It was applied at a thickness of 5 μm, 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 positive C plate (b1). When the phase difference of this positive C plate (b1) was measured, the light having a wavelength of 550 nm had a phase difference of about 200 nm (> λ / 8) when measured at 0 nm in the front direction and at an inclination of 30 °. there were.
[0190]
(Preparation of polarizing element (A))
A polarizing element (A) was obtained in the same manner as in Example 1 except that the positive C plate (b1) was used instead of the negative C plate (b1).
[0191]
(Production of liquid crystal display device with expanded viewing angle)
Using the obtained polarizing element (A), a viewing angle expansion system was assembled using the same liquid crystal display device and light source device as in Example 1. However, the diffusion adhesive layer, which is the viewing angle widening layer (W), is laminated on the upper polarizing plate (PL) of the liquid crystal display, and a triacetyl cellulose film with anti-glare treatment (AG: manufactured by Nitto Denko Corporation) , 80 μm TAC with AGS1). The obtained viewing angle widening liquid crystal display device is as shown in FIG. The characteristics were almost the same as those in Example 1. In Example 2, since the viewing angle widening layer (W) was disposed on the polarizing plate (PL), the viewing angle characteristics of the polarizing plate (PL) were not affected as compared with Example 1. And back-scattering of incident light such as illumination, and the contrast was slightly lowered. However, the viewing angle characteristics were superior to the conventional liquid crystal display device.
[0192]
Example 3
(Production of a linearly polarized reflective polarizer (a2))
The thickness of the thin film was alternately controlled by a feed block method so that polyethylene naphthalate (PEN) / naphthalene dicarboxylic acid-terephthalic acid copolyester (co-PEN) was alternately laminated to obtain a multilayer film in which 20 layers were laminated. . This multilayer film was uniaxially stretched. The stretching temperature was about 140 ° C., and the stretching ratio was about 3 times in the TD direction. The thickness of each thin layer in the obtained stretched film is approximately 0.1. It was about 1 μm. The obtained 20-layer laminated film stretched product was further laminated with 5 sheets, and a total of 100 laminated products were obtained as a linearly polarized reflective polarizer (a2). The linear polarization type reflection polarizer (a2) had a function of reflecting linearly polarized light in a wavelength band of 500 nm or more and 600 nm or less.
[0193]
(Preparation of polarizing element (A))
On both sides of the negative C plate (b1) obtained in Example 1, as a retardation layer (b2), a λ / 4 plate made of a uniaxially stretched polycarbonate film (Nitto Denko Corporation, NRF film, front retardation 135 nm) ) Was placed. Further, a linearly polarizing reflective polarizer (a2) was arranged outside the mirror so as to have the axial arrangement shown in FIG. 5 to obtain a polarizing element (A). That is, when the transmission polarization axis of the linear polarization type reflection polarizer (a2) obtained above is set to 0 °, the λ / 4 plate (b2): 45 °, C plate (b1: no axial orientation), λ / 4 plate (b2): −45 °, and transmission axis 90 ° of the linearly polarizing reflective polarizer (a2) on the emission side. These layers were laminated with a translucent acrylic adhesive (No. 725, 25 μm thick, manufactured by Nitto Denko Corporation). The substrate of the negative C plate (b1) was removed and used in the same manner as in Example 1.
[0194]
(Production of liquid crystal display device with expanded viewing angle)
Using the obtained polarizing element (A), a viewing angle expansion system was assembled using the same liquid crystal display device and light source device as in Example 1. Further, between the polarizing plate (PL) and the viewing angle widening layer (W), a polarizing plate viewing angle compensating retardation plate (Fuji Photo Film, 80 μm TAC biaxially stretched retardation plate) is inserted as a retardation layer (C). did. This is because light transmitted through the liquid crystal cell (LC) in the vicinity of the vertical direction is incident on the polarizing plate (PL) after being diffused in the viewing angle widening layer (W), and thus the viewing angle characteristics of the liquid crystal cell (LC) do not appear. The purpose of this is to suppress the appearance of the viewing angle characteristic of the polarizing plate (PL). The λ / 4 plate (B) was not arranged between the polarizing plate (PL) and the polarizing element (A).
[0195]
The obtained viewing angle enlarged liquid crystal display device is as shown in FIG. The characteristics were almost the same as those of Example 1, and the characteristics of the polarizing plate itself in the viewing direction insufficient region in the axial direction of the polarizing plate (± 45 ° oblique as viewed from the front of the screen) were improved.
[0196]
Example 4
(Preparation of polarizing element (A))
As a retardation layer (b4), a polycarbonate film is biaxially stretched as a retardation layer (b4) between two layers of the linear polarization type reflection polarizer (a2) obtained in Example 3 in which transmission polarization axes are orthogonally arranged to each other. The resulting retardation film (front retardation: 270 nm, Nz coefficient = 1.5) was adhered according to FIG. 9 to produce a polarizing element (A). The retardation film was produced by stretching and orienting a non-stretched polycarbonate film manufactured by Kaneka Chemical Industry Co., Ltd. using a biaxial stretching machine. A translucent acrylic adhesive (Nitto Denko Corporation, No. 7, 25 μm thick) was used for bonding the layers.
[0197]
(Production of liquid crystal display device with expanded viewing angle)
Using the obtained polarizing element (A), a backlight system was produced in the same manner as in Example 1.
[0198]
Next, a color STN liquid crystal (10.4 inches) was arranged as a liquid crystal cell (LC) in a monochromatic light source backlight using the polarizing element (A). The upper and lower polarizing plates (PL) were replaced with SEG1425DU manufactured by Nitto Denko Corporation and used. Further, between the liquid crystal cell (LC) and the polarizing plate (PL), as a retardation layer (C), an STN compensation retardation plate (NRF film manufactured by Nitto Denko Corporation, frontal retardation 430 nm, polycarbonate, thickness 50 μm, and the thickness of the adhesive layer was 25 μm). As the viewing angle widening layer (W), a microlens array sheet (equivalent to 90% haze, lens pitch of about 20 μm) having a surface shape was disposed on the polarizing plate (PL) surface side. These were bonded together with a translucent acrylic adhesive (No. 7, 25 μm thick, manufactured by Nitto Denko Corporation).
[0199]
The obtained viewing angle widening liquid crystal display device is as shown in FIG. The viewing angle widening liquid crystal display device has a low front-side maximum contrast of the basic liquid crystal display device of about 20 but does not show gradation reversal similarly to the first embodiment, and has a wide practical viewing angle range. Thing was obtained.
[0200]
Example 5
(Production of Circularly Polarized Reflective Polarizer (a1))
A coating liquid containing four layers of cholesteric liquid crystal polymer having different selective reflection center wavelengths and a solvent is applied to a rubbed surface of a triacetyl cellulose film which has been rubbed with a polyimide alignment film in advance, and has a broadband circularly polarized reflection. A polarizer (a1) was obtained. As the liquid crystal material used, four types of cholesteric liquid crystal polymers having selective reflection central wavelengths of 460 nm, 510 nm, 580 nm, and 660 nm were produced based on European Patent Application Publication No. 0834754.
[0201]
Cholesteric liquid crystal polymer is represented by the following formula 2:
Embedded image

And a polymerizable nematic liquid crystal monomer A represented by the following formula:
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 1 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 1 shows the selective reflection wavelength band.
[0202]
[Table 1]

[0203]
The cholesteric liquid crystal polymer was dissolved in methylene chloride to prepare a 10% by weight solution. The solution is applied to an alignment base material to a thickness of about 1. Coating was performed with a wire bar so that the thickness became 5 μm. An 80 μm-thick triacetyl cellulose film (manufactured by Fuji Photo Film Co., Ltd., TD-TAC) was used as an alignment base material, and a polyimide layer was formed on the surface of the triacetyl cellulose film with 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.
[0204]
After 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 bonded together with a transparent isocyanate-based adhesive AD244 (manufactured by Tokuseki Kogyo Kogyo). The R and G liquid crystal thin film surfaces were bonded together, and the G-side triacetyl cellulose substrate was peeled off. Similarly, after the B color was bonded to the G liquid crystal thin film surface, the R side triacetyl cellulose substrate was peeled off. As a result, a cholesteric liquid crystal composite layer having a thickness of about 10 μm in which four liquid crystal layers were laminated in order from the short wavelength side was obtained. The obtained circularly polarizing reflective polarizer (a1) comprising a cholesteric liquid crystal composite layer had a selective reflection function at 430 nm to 710 nm.
[0205]
(Preparation of Polarizing Element (A) and Backlight System Using It)
The obtained circularly polarizing reflective polarizer (a1) is adhered to both sides of the negative C plate (b1) prepared in Example 1 with a translucent adhesive (No. 7, 25 μm thick, manufactured by Nitto Denko Corporation). Together, a polarizing element (A) was produced. As the upper and lower circularly polarizing reflective polarizers (a1), those having the same circularly polarized light direction were used.
[0206]
The obtained polarizing element (A) was placed in a direct backlight (D) manufactured by Tama Electric Industry using cold cathode tubes (435 nm, 545 nm, 610 nm) having bright lines at three wavelengths. In this case as well, light rays are emitted in the normal direction, but the transmitted light rays sharply decrease at an angle of 20 ° or more, halved near 30 °, and decreased to about 10% of the front luminance near 45 °. Since the polarizing element (A) corresponds to the entire range of visible light, it functioned as a light-collecting element that transmits only the front in the entire range of visible light and does not transmit in the oblique direction.
[0207]
(Production of liquid crystal display device with expanded viewing angle)
Using the obtained backlight system, the same components as those of the laminate of the liquid crystal cell (LC) and the viewing angle widening layer (W), which were the same as in Example 2, were overlaid to obtain a viewing angle widening liquid crystal display device. . The obtained viewing angle widening liquid crystal display device is as shown in FIG.
[0208]
Example 6
(Preparation of Polarizing Element (A) and Backlight System Using It)
As a linear polarization type reflection polarizer (a2), DBEF manufactured by 3M was used. FIG. 6 shows a retardation film (front retardation 140 nm, Nz coefficient = 2) obtained by biaxially stretching a polycarbonate film as a retardation layer (b3) with respect to the linear polarization type reflection polarizer (a2). And 7 were adhered to produce a polarizing element (A). The retardation film was produced by stretching and orienting a non-stretched polycarbonate film manufactured by Kaneka Chemical Industry Co., Ltd. using a biaxial stretching machine. A translucent acrylic adhesive (Nitto Denko Corporation, No. 7, 25 μm thick) was used for bonding the layers.
[0209]
A light diffusion plate (D: made by Kimoto, haze about 90%) is arranged in a side light type backlight (E: made by Stanley Electric) using a cold cathode tube (435 nm, 545 nm, 610 nm) having a bright line at three wavelengths as a light source device. Then, the polarizing element (A) was disposed thereon. On the lower surface of the backlight, a diffuse reflection plate (F) in which matte PET was subjected to silver deposition was arranged.
[0210]
(Production of liquid crystal display device with expanded viewing angle)
Using the obtained backlight system, a viewing angle widening liquid crystal display device shown in FIG. 16 was produced. As a liquid crystal cell (LC), a color TFT liquid crystal (10.4 inches) manufactured by Toshiba was used. As the viewing angle expanding layer (W), a microlens array sheet having a surface shape was used. The polarizing plate (PL) used was SEG1425DU manufactured by Nitto Denko Corporation.
[0211]
The microlens array sheet is equivalent to haze 90. The lens pitch is about 20 μm, and it is manufactured by transferring and forming from a brass die-ground product. The base film is 50 μm clear TAC manufactured by Fuji Photo Industry Co., Ltd. The shape transfer resin was a UV-curable epoxy resin (KR410, manufactured by Asahi Denka Kogyo Co., Ltd.). After releasing the mold surface with a silicone resin, the epoxy resin was dropped. After uniformly spreading the epoxy resin over the entire surface using a glass rod, the substrate film was bonded, and the shape formed by ultraviolet polymerization (10 mW for 30 seconds) was transferred onto the film. With respect to the surface of the upper polarizing plate (PL) in FIG. 16, the substrate film was arranged on the polarizing plate (PL) side, and the irregularity transfer surface was arranged on the side facing the air, and bonded. In the obtained viewing angle widening liquid crystal display device, no gradation inversion was observed at ± 60 ° from the front.
[0212]
In this system, the microlens array with a wide viewing angle interfered with the black matrix of the liquid crystal display device, and moiré occurred. However, moiré could be mitigated by inclining the bonding angle of the microlens array by 45 °. At this time, there was no interference with a polarizing element comprising a polarizing reflector.
[0213]
Example 7
(Preparation of polarizing element (A))
As a linear polarization type reflection polarizer (a2), DBEF manufactured by 3M was used. On both sides of the negative C plate (b1) obtained in Example 1, as a retardation layer (b2), a broadband λ / 4 retardation plate (Nitto) formed by laminating two uniaxially stretched polycarbonate films on different axes. An NRF film manufactured by Denko K.K. and a front retardation of 140 nm, and an NRZ film, a front retardation of 270 nm and a laminate having an Nz coefficient of 0.5 were arranged. FIG. 17 shows the lamination axis relation of the broadband λ / 4 phase difference plate (b2). This is because the linear polarization type reflective polarizer (a2) has a wide band covering the entire visible light range, so that the wavelength characteristics of condensing and collimating light are aligned, and the reflection by the wavelength when reflecting the incident light in the oblique direction. This is to reduce the difference in rates. Thereby, when the emitted light is dimmed in the oblique direction, the difference in the dimming rate due to the color becomes smaller, and the light can be narrowed down with little change in color tone.
[0214]
Further, a linearly polarizing reflective polarizer (a2) was arranged outside the mirror so as to have the axial arrangement shown in FIG. 5 to obtain a polarizing element (A). That is, when the transmission polarization axis of the linear polarization type reflection polarizer (a2) on the incident side is set to 0 °, the λ / 4 plate (b2): 45 °, and the C plate (B1: no axial direction), λ / 4 plate (b2): −45 °, and transmission axis 90 ° of the linearly polarizing reflective polarizer (a2) on the emission side. These layers were laminated with a translucent acrylic adhesive (No. 7, manufactured by Nitto Denko Corporation, 25 μm thick). The substrate of the negative C plate (b1) was removed and used in the same manner as in Example 1.
[0215]
(Production of liquid crystal display device with expanded viewing angle)
Using the obtained polarizing element (A), a viewing angle expanding system similar to that of Example 1 was assembled. The obtained viewing angle widening liquid crystal display device is as shown in FIG. However, a hologram diffusion plate was disposed as the viewing angle widening layer (W). As a backlight, a sidelight type backlight (E) made by Stanley Electric using a three-wavelength (435 nm, 545 nm, 610 nm) cold cathode tube was used. A combination of a diffusion plate (haze of about 90) was used. As a liquid crystal cell (LC), a TFT liquid crystal cell (11.3 inches) manufactured by Sharp was used.
[0216]
The characteristics were almost the same as those of Example 1. The characteristics of the polarizing plate itself in the viewing angle insufficient region in the axial direction of the polarizing plate (the direction ± 45 ° oblique as viewed from the front of the screen) are improved.
[0219]
Comparative Example 1
The polarizing element (A) including the reflective polarizer (a) and the retardation plate (b) was deleted from the viewing angle widening liquid crystal display devices of Examples 1 to 7. In any of the liquid crystal display devices, the viewing angle characteristics are averaged due to the diffusion effect of the viewing angle widening layer (W). Then, the contrast was lowered.
[0218]
Further, in the region where the inclination angle is ± 45 ° or more from the normal direction, which is the region where the gradation is inverted, even if averaging, only the average of the image whose gradation is inverted can be obtained. For this reason, the effect of the viewing angle widening layer (W) was not observed, gradation reversal occurred, and an unnatural change in brightness was observed in gray scale display.
[0219]
Comparative Example 2
In Example 6, a parallel light source was obtained using a light control film manufactured by 3M instead of the polarizing element (A). However, interference occurred between the microlens array and the black matrix of the pixels of the liquid crystal display device, and moire was visually recognized. Therefore, rotation of the microlens array was attempted to reduce the light emission. However, when the microlens array was rotated, moire was generated between the microlens array and the pitch of the light control film, and both could not be erased.
[0220]
Comparative Example 3
In the same manner as in Example 3, except that a commercially available iodine-based absorption dichroic polarizer (Nitto Denko Corporation, NPF-EG1425DU) was used instead of the linear polarization type reflection polarizer (a2). A polarizing element was produced in various combinations. Using the polarizing element, a viewing angle widening liquid crystal display device similar to that of Example 1 was manufactured. However, although the viewing angle limiting effect was obtained by the transmission characteristics in the front direction and the absorption characteristics in the oblique direction, the absorption loss was remarkable, the brightness in the front was not improved, and only a very dark display was obtained.
[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 in FIG. 1, FIG. 3, FIG. 4, FIG. 6, and FIG.
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 a conceptual diagram of a viewing angle widening liquid crystal display device of Example 1.
FIG. 12 is a conceptual diagram of a viewing angle widening liquid crystal display device according to a second embodiment.
FIG. 13 is a conceptual diagram of a viewing angle widening liquid crystal display device according to a third embodiment.
FIG. 14 is a conceptual diagram of a viewing angle widening liquid crystal display device according to a fourth embodiment.
FIG. 15 is a conceptual diagram of a viewing angle widening liquid crystal display device according to a fifth embodiment.
FIG. 16 is a conceptual diagram of a viewing angle widening liquid crystal display device according to a sixth embodiment.
FIG. 17 is a conceptual diagram showing a lamination axis relationship of a two-layer different axis broadband λ / 4 phase difference plate (b2) in Example 7.
FIG. 18 is a conceptual diagram of a viewing angle widening liquid crystal display device according to a seventh embodiment.
[Explanation of symbols]
a reflective polarizer
a1 Circularly polarized reflective polarizer
a2 Linear polarization type reflective polarizer
b retardation layer
A Polarizing element
B λ / 4 plate
C compensation retardation layer
D Diffuser
E Sidelight type light guide plate or direct type backlight
F Diffuse reflector
AG anti-glare layer
LC liquid crystal cell
PL polarizing plate
W Viewing angle expansion layer

Claims (17)

Using a polarizing element (A) in which a retardation layer (b) is arranged between at least two reflective polarizers (a) in which the wavelength bands of polarized light selective reflection overlap each other, a parallel light source of a diffuse light source is used. A backlight system that has been lightened,
A liquid crystal cell through which the collimated light passes,
Polarizing plates arranged on both sides of the liquid crystal cell,
A viewing angle expansion layer disposed on the viewing side of the liquid crystal cell for diffusing transmitted light,
A viewing angle widening liquid crystal display device characterized by containing at least 2. The viewing angle widening liquid crystal display device according to claim 1, wherein the selective reflection wavelengths of at least two layers of the reflective polarizers (a) overlap each other in a wavelength range of 550 nm ± 10 nm. The reflective polarizer (a) is a circularly polarized reflective polarizer (a1) that transmits certain circularly polarized light and selectively reflects opposite circularly polarized light,
A phase difference layer (b1) having a front phase difference (normal direction) of substantially zero and a phase difference of λ / 8 or more with respect to incident light that is incident at an angle of 30 ° or more with respect to the normal direction; 3. The viewing angle widening liquid crystal display device according to claim 1, wherein 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
A phase difference layer (b1) having a front phase difference (normal direction) of substantially zero and a phase difference of λ / 4 or more with respect to incident light inclined at an angle of 30 ° or more with respect to the normal direction; )
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,
3. The viewing angle widening liquid crystal display device according to claim 1, wherein the liquid crystal display device 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,
3. The viewing angle widening liquid crystal display device according to claim 1, wherein the liquid crystal display device 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,
3. The viewing angle widening liquid crystal display device according to claim 1, wherein the liquid crystal display device is arranged. The viewing angle expansion according to any one of claims 1 to 4, wherein the retardation layer (b1) is formed by fixing the planar orientation of a cholesteric liquid crystal phase having a selective reflection wavelength range other than the visible light range. Liquid crystal display. The viewing angle widening liquid crystal display device according to any one of claims 1 to 4, wherein the retardation layer (b1) is one in which the homeotropic alignment state of the rod-shaped liquid crystal is fixed. The viewing angle widening liquid crystal display device according to any one of claims 1 to 4, wherein the retardation layer (b1) is a layer in which a nematic phase or a columnar phase alignment state of the discotic liquid crystal is fixed. The viewing angle widening liquid crystal display device according to any one of claims 1 to 4, wherein the retardation layer (b1) is formed by biaxially orienting a polymer film. The phase difference layer (b1) is a layer obtained by fixing the orientation of an inorganic layered compound having a negative uniaxial property such that the optical axis is in the direction normal to the surface. 2. The viewing angle widening liquid crystal display device according to item 1. The viewing angle widening liquid crystal display device according to claim 3, wherein a cholesteric liquid crystal is used as the circular polarization type reflective polarizer (a <b> 1). A λ / 4 plate is arranged on the viewing side (liquid crystal cell side) of the circular polarization type reflective polarizer (a1), and the axial direction of the linearly polarized light obtained by transmission and the transmission through the lower surface side (light source side) of the liquid crystal display device 13. The viewing angle widening liquid crystal display device according to claim 3, wherein the liquid crystal display device is arranged in an axial direction. The viewing angle according to any one of claims 4 to 11, wherein a stretched product of a multilayer laminated film material of a resin material having a different refractive index and a retardation value is used as the linear polarization type reflection polarizer (a2). Enlarged liquid crystal display. An axial direction of linearly polarized light obtained by transmission of the linearly polarized reflective polarizer (a2) and a transmission axis direction of a polarizing plate on the lower surface side (light source side) of the liquid crystal display device are arranged. Item 15. The viewing angle widening liquid crystal display device according to item 4 to 11 or 14. The viewing angle widening liquid crystal display device according to any one of claims 1 to 15, wherein a diffusion plate having substantially no backscattering or depolarization is used as the viewing angle widening layer. The viewing angle widening liquid crystal display device according to any one of claims 1 to 16, wherein each layer is laminated using a translucent adhesive or pressure-sensitive adhesive.

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