JP3699160B2 - Liquid crystal display element using optical anisotropic element - Google Patents

Description

【００２６】
【化２】

【００２７】
また、本発明における、コレステリック相を呈する液晶性高分子を下記に列挙する。
【００２８】
【化３】

【００２９】
【化４】

【００３０】
本発明の場合、光学的チルト角を厚さ方向で連続的に変化させるためには、下記の処理が必要になる。
一般に、ネマチック液晶を用いた液晶セルの場合、該液晶層の両側を、ラビング処理した配向膜で挟むことにより、液晶分子の光軸が一定の方向へ配向している。すなわち、液晶層の両側にある配向膜の配向規制力により、液晶分子は厚さ方向で均一な配向をしているわけであり、該配向膜の配向規制力を両側でアンバランスにする事により、厚さ方向で連続的に分子の配向を変化させることが出来る。この考え方は、本発明の液晶性高分子にも応用することが出来る。
具体的には、ラビング処理した有機配向膜あるいは無機配向膜の形成された基板に液晶性高分子を塗布し、該液晶層の片側を開放系（空気層）のまま液晶相形成温度まで昇温するか、あるいは前記配向膜と、それとは異なった表面処理を施した配向膜で挟んだまま液晶相形成温度まで昇温することである。但し、上述の配向膜の配向規制力が十分に強い場合には、該液晶性高分子層の片側を解放系（空気層）のままであっても、該液晶性高分子の光学的チルト角が厚さ方向で同じである場合も存在する。
【００３１】
これにより該液晶は、光学的チルト角が厚さ方向で連続的に変化した斜め配向をし、その後の冷却により配向を保ったまま、常温では固体状態をとる。この場合、配向膜近傍でのチルト角は、液晶性高分子素材、配向膜素材、ラビング等で、コントロ−ルすることが出来、そのチルト角は、０°乃至８５°が好ましく、０°乃至５０°が更に好ましい。
また、空気層、あるいは異なった表面処理を施した配向膜近傍のチルト角は、液晶性高分子素材、可塑剤、バインダ−、界面活性剤、等でコントロ−ルすることが出来、更には、これら可塑剤、バインダ−、界面活性剤、等で、チルト角の厚さ方向の配向変化の度合いをコントロ−ルすることも可能である。
【００３２】
これら可塑剤の好ましい例としては、使用する液晶性高分子と相溶するものであれば特に制限はなく、耐熱性付与の観点からは、反応性の置換基を有することが好ましい。また、液晶性高分子に対する添加量は、重量比で０．１ｗｔ％乃至５０ｗｔ％が好ましい。
また、バインダ−の好ましい例としては、使用する液晶性高分子の配向を著しく阻害するものでなければ特に制限はなく、市販のポリマ−を使用することが出来る。本発明者の鋭意研究の結果、ディスコティック液晶をメソゲン基として有する液晶性高分子の場合はセルロ−ス系高分子誘導体が極めて好ましいことが見いだされた。
【００３３】
液晶相形成温度は構造、あるいは分子量等に固有のものであるが、異なるものを二種以上混合するか、又は前述の可塑剤を混合する事により、任意に調整する事ができる。
本発明に用いる液晶性高分子の液晶相−固相転移温度としては、好ましくは７０℃以上、３００℃以下、特に好ましくは７０℃以上、２５０℃以下である。
【００３４】
上記の有機配向膜として用いるポリマーとしては、ポリイミド、ポリスチレン誘導体など、また水溶性のものとしては、ゼラチン、ポリビニルアルコール、カルボキシメチルセルロースなどが挙げられる。これらは全てラビング処理を施すことにより、液晶性高分子を斜めに配向させることができる。
【００３５】
ＬＣＤの配向膜として広く用いられているポリイミド膜は有機配向膜として好ましく、これはポリアミック酸（例えば、日立化成製 ＬＱ／ＬＸシリーズ、日産化学製 ＳＥシリーズ等）を基板面に塗布し１００〜３００℃で０．５〜１時間焼成の後ラビングする事により得られる。
【００３６】
また、前記ラビング処理は、ＬＣＤの液晶配向処理工程として広く普及しているものと同一な工程であり、配向膜の表面を紙やガーゼ，フェルト，ラバー、或いはナイロン，ポリエステル繊維などを用いて一定方向にこすることにより配向を得る方法である。一般的には長さと太さが均一な繊維を平均的に植毛した布などを用いて数回程度ラビングを行う。
【００３７】
また、無機斜方蒸着膜の蒸着物質としてはＳｉＯを代表としＴｉＯ₂、ＭｇＦ₂、ＺｎＯ₂等の金属酸化物やフッ化物、Ａｕ，Ａｌ等の金属が挙げられる。尚、金属酸化物は高誘電率のものであれば斜方蒸着物質として用いることができ、上記に限定されるものではない。
【００３８】
本発明の光学異方素子を構成する、光学的に負の一軸性でその光軸がフイルムの法線方向にある光学異方素子（Ｂ）としては、光透過率が８０％以上であると同時に、フイルム面内の主屈折率をｎｘ、ｎｙ、厚み方向の主屈折率をｎｚ、フイルムの厚みをｄとしたとき、三軸の主屈折率の関係が ｎｚ＜ｎｙ＝ｎｘ を満足し、式 ｛（ｎｘ＋ｎｙ）／２−ｎｚ｝×ｄ で表されるレタデーションが２０ｎｍから４００ｎｍである事が好ましく、２０ｎｍから１５０ｎｍであることが更に好ましい。
但し、ｎｘとｎｙの値は厳密に等しい必要はなく、ほぼ等しければ十分である。具体的には、｜ｎｘ−ｎｙ｜／｜ｎｘ−ｎｚ｜≦０．３ であれば実用上問題はない。 ｜ｎｘ−ｎｙ｜×ｄ で表される正面レタデーションは、５０ｎｍ以下である事が好ましく、２０ｎｍ以下である事がさらに好ましい。
【００３９】
該光学異方素子（Ｂ）は、ゼオネックス（日本ゼオン）、ＡＲＴＯＮ（日本合成ゴム）、フジタック（富士写真フイルム）などの商品名で売られている固有複屈折率が小さい素材、あるいは、ポリカーボネート、ポリアリレート、ポリスルフォン、ポリエーテルスルフォンなどの固有複屈折率が大きい素材を、溶液流延、溶融押し出し等によって製膜し作成する事が出来る。
【００４０】
本発明の光学異方素子は、液晶表示素子において、液晶セルによる複屈折を補償するものであるから、光学異方素子の波長分散は、液晶セルと等しい事が好ましい。すなわち、光学異方素子の４５０、５５０μｍの光によるレタデーションをそれぞれＲ450、Ｒ550とすれば、波長分散を表わすＲ450／Ｒ550値は、１．０以上である事が好ましい。
【００４１】
本発明の液晶表示素子をカラー液晶表示装置として用いる場合カラーフィルターが必要となる。その時に用いるカラーフィルターとしては、例えば小林駿介編著「カラー液晶ディスプレイ」産業図書、１７２頁〜１７３頁、２３７頁〜２５１頁、あるいは日経マイクロデバイス編「フラットパネル・ディスプレイ１９９４」日経ＢＰ社、２１６頁等に記載のあるゼラチンやカゼイン、ＰＶＡ等の基質に重クロム酸塩を加えて感光性を付与し、フォトリソグラッフィー法によってパターンニングした後、染色して得られる染色フイルター、印刷フイルター、電着フイルター、あるいは顔料分散フイルター等が好ましい。
但し、これ以外にも、色純度、寸法精度、さらには耐熱性の高いものであれば方式にこだわらず、使用する事が出来る。
【００４２】
また、本発明の液晶表示装置に用いる液晶としては、例えば日本学術振興会第１、２委員会編「液晶デバイスハンドブック」日刊工業新聞社、１０７頁〜２１３頁記載のネマティック液晶が好ましい。この液晶分子の長軸は、液晶セルの上下基板間でほぼ９０°ツイスト配向したものであり、入射した直線偏光は印加電界がない場合、液晶セルの旋光性によって、９０°偏光方向を変えて液晶セルから出射する事になる。しきい値以上の十分高い電界を印加した時には、液晶分子の長軸が電界方向に向きを変え、電極面に垂直にならび、旋光性は殆ど消失する。したがって、この旋光の効果を十分に発揮させるために、ツイスト角は７０°〜１００°であり、８０°〜９０°がさらに好ましい。
【００４３】
この電界による液晶分子の配列の欠陥（ディスクリネーション）を少なくするため、液晶分子にあらかじめプレチルト角を与えておく事が好ましい。プレチルト角は５°以下が好ましく、さらに２°〜４°が好ましい。
このツイスト角、プレチルト角については、岡野光治、小林駿介共編「液晶応用編」培風館、１６頁〜２８頁に記載されている。
【００４４】
さらに液晶セルの屈折率異方性Δｎと、液晶セルにおける液晶層の厚みｄとの積Δｎｄの値は、例えば日本学術振興会第１４２委員会編「液晶デバイスハンドブック」日刊工業新聞社、３２９頁〜３３７頁に記載されているように、ｄが大きくなればコントラストは改良されるものの、応答速度が遅く、また視野角も悪くなるため、３００ｎｍ〜１０００ｎｍの範囲が好ましく、３００ｎｍ〜６００ｎｍの範囲がより好ましい。
【００４５】
本発明の液晶表示装置に印加される信号は、例えば日本学術振興会第１４２委員会編「液晶デバイスハンドブック」日刊工業新聞社、３８７頁〜４６５頁、あるいは岡野光治、小林駿介共編「液晶 応用編」培風館、８５頁〜１０５頁等に記載されている様に、５Ｈｚ〜１００Ｈｚの交流で、電圧は２０Ｖ以下、好ましくは８Ｖ以下である。たとえばノーマリーホワイトモードでは、印加電圧が０〜１．５Ｖで明表示、１．５Ｖ〜３．０Ｖで中間調表示、３．０Ｖ以上で暗表示を行っている場合が多い。
【００４６】
本発明において透明フィルム上に液晶性高分子を含む層を設けた場合、液晶セルに該光学異方素子を装着する時に、液晶性高分子層を液晶セル寄りに配置する場合と、透明フィルムを液晶セル寄りに配置する場合があるが、本発明においては、どちらに配置しても構わない。しかし、補償能を最大限に発揮するには、液晶性高分子層を液晶セル寄りに配置する方が好ましい。
【００４７】
【実施例】
以下、本発明を実施例に基づいて詳細に説明する。
【００４８】
実施例１
ゼラチン薄膜（０．１μｍ）を塗設したトリアセチルセルロースの１００μｍ厚フィルム（富士写真フイルム（株）製）上に長鎖アルキル変性ポバール（ＭＰ２０３ ：商品名 クラレ製）を塗布し、４０℃温風にて乾燥させた後、ラビング処理を行い配向膜を形成した。面内の主屈折率をｎx ’、ｎy ’、厚さ方向の屈折率をｎz ’、厚さをｄ’とした時、トリアセチルセルロースフィルムは、｜ｎx’−ｎy ’｜×ｄ’＝３ｎｍ、｛（ｎx ’＋ｎy ’）／２−ｎz ’｝×ｄ’＝７０ｎｍであり、ほぼ負の一軸性であり、光軸がほぼフイルム法線方向にあった。
【００４９】
この配向膜上に、前述した液晶性高分子ＴＥ−６ １．６ｇ、フェノ−ルＥＯ変性（ｎ＝１）アクリレート（Ｍ１０１ 東亜合成） ０．４ｇ、セルロ−スアセテ−トブチレ−ト（ＣＡＢ５３１−１ イ−ストマンケミカル） ０．０５ｇ、イルガキュアー９０７ ０．０１ｇを３．６５ｇのメチルエチルケトンに溶解した塗布液を、ワイヤ−バ−で塗布（＃４バ−使用）し、金属の枠に貼りつけて１１５℃の高温槽中で３分間加熱し、液晶を配向させた後、室温まで急冷して、液晶性高分子を含む層を有する光学異方素子を作成した。
【００５０】
このようにして得られた光学異方素子のレターデーションを、ラビング軸を含み位相差板面に垂直な面において、ラビング軸を起点に４０°から１４０°までを５°刻みで、島津製作所製エリプソメーター（ＡＥＰ−１００）を用いて測定したところ、レターデーションが０となる方向は存在しなかった。レターデーション値の絶対値が最小となる方向は、フィルム法線方向でも面方向でもなかった。また、ラビング軸を含み位相差板面に垂直な面において、ラビング軸を起点に４０°から１４０°までを５°刻みでレタ−デ−ション値を測定し、更に、測定部分の液晶性高分子を除去した後の支持体の光学特性を同様に測定した。また、液晶性高分子層を厚さ方向に１０分割し、この実測値をシュミレ−トしたところ、液晶性高分子層のチルト角は、２０°から７０°まで連続的に変化しており、レターデーションは７０ｎｍであった。
【００５１】
液晶の異常光と常光の屈折率の差と液晶セルのギャップサイズの積が４２０ｎｍで、ねじれ角が９０度のＴＮ型液晶セルに、上記光学異方素子１枚を、各光学素子が図１と同様な配置になるように装着した。各光学素子の装着角度は、図５に示したとおりである。光学異方素子のレターデーション値の絶対値が最小となる方向を液晶セル基板上に正射影した方向と、該光学異方素子に近い方の液晶セル基板のラビング方向のなす角αは２２５°とした。
【００５２】
実施例２
図３のような構成で、実施例１に用いた光学異方素子を、実施例１と同じＴＮ型液晶セルに２枚、液晶セルを挟むように配置した。各光学素子の装着角度は図６に示したとおりである。α１は１８０°、α２は１８０°とした。
【００５３】
比較例１
実施例１と同じＴＮ型液晶セルに、光学異方素子を装着せずに、図７のように配置した。
【００５４】
比較例２
図３のような構成で、実施例１に用いた光学異方素子を、実施例１と同じＴＮ型液晶セルに２枚、液晶セルを挟むように配置した。各光学素子の装着角度は図８に示したとおりである。α１は０°、α２は０°とした。
【００５５】
実施例３
６０μｍのＰＣフィルム上にポリイミド層を形成しラビング処理を行い、配向膜を形成した。面内の主屈折率をｎx ’、ｎy ’、厚さ方向の屈折率をｎz ’、厚さをｄ’とした時、ＰＣフィルムは、｜ｎx ’−ｎy ’｜×ｄ’＝５ｎｍ、｛（ｎx ’＋ｎy ’）／２−ｎz ’｝×ｄ’＝１００ｎｍであり、ほぼ負の一軸性であり、光軸がほぼフイルム法線方向にあった。
この配向膜上に前述した液晶性高分子ＴＥ−７にメチレンクロライドを加え、全体として２０ｗｔ％溶液とし、スピンコ−トにより２０００ｒｐｍで塗布を行った。８５℃まで昇温、熱処理した後、室温まで急冷し、およそ０．５μｍの液晶層を形成させ、光学異方素子を作製した。
実施例１と同様の光学測定を行い、液晶性高分子層の光学的チルト角をシュミレ−トすると、１５°から３５°まで変化しており、レターデーションは８０ｎｍであった。
【００５６】
延伸したＰＶＡにヨウ素を吸着させて作製される偏光膜に、液晶セル側の保護膜として、直接光学異方素子を、液晶性高分子層を液晶セル側にして貼り合わせた。そして、図３のような構成で、実施例１と同じＴＮ型液晶セルに２枚、液晶セルを挟むように配置した。各光学素子の装着角度は図９に示したとおりである。α１は１８０°、α２は１８０°とした。
【００５７】
（視野角の測定）
液晶セルに対して、５５Ｈｚ矩形波で電圧を印加した。白表示１Ｖ、黒表示５Ｖの透過率の比（白表示）／（黒表示）をコントラスト比として、正面方向および上／下および左／右方向へ傾いた方向からのコントラスト比測定を大塚電子製ＬＣＤ−５０００にて行った。正面コントラスト、および、コントラストが１０以上かつ階調反転が起きない上／下および左／右の視野角を求め、表１にまとめた。
【００５８】
【表１】

【００５９】
表１から明らかな様に、本発明の光学異方素子は、正面コントラストを低下させる事なく、視野角を広げる事が出来る。
【００６０】
【発明の効果】
本発明によれば、ＴＮ型液晶表示素子の視角特性が改善され、視認性にすぐれる高品位表示の液晶表示素子を提供することができる。また、本発明をＴＦＴやＭＩＭなどの３端子、２端子素子を用いたアクティブマトリクス液晶表示素子に応用しても優れた効果が得られることは言うまでもない。
【図面の簡単な説明】
【図１】本発明の液晶表示素子の構成の１実施例を説明する図
【図２】図１を原点からｚ軸方向に見た場合の軸構成を説明する図
【図３】本発明の液晶表示素子の構成の１実施例を説明する図
【図４】図３を原点からｚ軸方向に見た場合の軸構成を説明する図
【図５】実施例１の軸構成を説明する図
【図６】実施例２の軸構成を説明する図
【図７】比較例１の軸構成を説明する図
【図８】比較例２の軸構成を説明する図
【図９】実施例３の軸構成を説明する図[0001]
[Industrial application fields]
The present invention relates to a liquid crystal display element with improved display contrast and viewing angle characteristics of display colors.
[0002]
[Prior art]
CRT, which is the mainstream of display devices for OA equipment such as Japanese word processors and desktop personal computers, has been converted into a liquid crystal display element having the great advantages of being thin and light and low power consumption. Many of the liquid crystal display elements (hereinafter referred to as LCDs) that are currently popular use twisted nematic liquid crystals. Display systems using such liquid crystals can be broadly divided into two systems, birefringence mode and optical rotation mode.
[0003]
LCD using birefringence mode is a simple matrix electrode structure with no active elements (thin film transistors and diodes) because the twist angle of the liquid crystal molecular alignment is twisted 90 ° or more and has steep electro-optical characteristics. However, large-capacity display can be obtained by time-division driving. However, if the response speed is slow (several hundred milliseconds) and gradation display is difficult, the display performance of liquid crystal display elements using active elements (such as TFT-LCD and MIM-LCD) is exceeded. Absent.
[0004]
TFT-LCD and MIM-LCD use a rotation mode display system (TN type liquid crystal display element) in which the alignment state of liquid crystal molecules is twisted by 90 °. This display method is the most powerful method compared with other types of LCDs because it has a high response speed (several + milliseconds), easily obtains black and white display, and exhibits high display contrast. However, since the twisted nematic liquid crystal is used, there is a problem in viewing angle characteristics that the display color and the display contrast change depending on the viewing direction due to the principle of the display method, and the display performance of the CRT cannot be exceeded.
[0005]
SID '92 Digest p. 798 and the like, a method has been proposed in which pixels are divided and the tilt direction at the time of voltage application is reversed to compensate the viewing angle characteristics. According to this method, the viewing angle characteristic regarding the gradation inversion in the vertical direction is improved, but the contrast viewing angle characteristic is hardly improved.
[0006]
As seen in JP-A-4-229828, JP-A-4-258923, etc., an attempt is made to expand the viewing angle by arranging a retardation film between a pair of polarizing plates and a TN type liquid crystal cell. A method has been proposed.
[0007]
The retardation film proposed in the above patent publication has a phase difference of almost zero in the direction perpendicular to the surface of the liquid crystal cell, and does not exert any optical action from the front, and is tilted. This is to compensate for the phase difference that occurs in the liquid crystal cell. However, even with these methods, the viewing angle of the LCD is still insufficient, and further improvements are desired.
[0008]
In JP-A-4-366808 and JP-A-4-366809, a liquid crystal cell including a chiral nematic liquid crystal with an inclined optical axis is used as a retardation film, but the viewing angle is improved. The cost is high and it is very heavy.
[0009]
Further, in JP-A-6-75116, EP0576304A1, and JP-A-6-214116, a TN type LCD is obtained by using a phase difference plate that exhibits optically negative uniaxiality and whose optical axis is inclined. There has been proposed a method for improving the viewing angle characteristics.
According to this method, the viewing angle is improved as compared with the conventional one, but it is still difficult to realize a viewing angle wide enough to consider alternatives to CRT.
[0010]
As a result of intensive studies, an optically anisotropic element having an optically negative uniaxial property and its optical axis being inclined from the normal direction of the film, and an optically negative uniaxial property having an optical axis that is normal to the film. It has been found that the viewing angle characteristics of a TN type LCD in black and white display are remarkably improved by the retardation plate having the characteristics of the optical anisotropic element in the direction.
[0011]
However, in this method, the effect of improving the viewing angle as viewed from the contrast in black and white display is remarkable, but more advanced compensation is required for the inversion of the gradation depending on the viewing angle.
[0012]
[Problems to be solved by the invention]
The present invention provides a liquid crystal display element with improved display contrast, gradation characteristics and viewing angle characteristics of display colors without reducing front contrast in a TN liquid crystal cell.
[0013]
[Means for Solving the Problems]
The above problems have been achieved by the following means.
(1) Between two electrode substrates Twist angle is 70-100 degrees The liquid crystal is sandwiched TN type A liquid crystal display element comprising a liquid crystal cell, two polarizing elements disposed on both sides of the liquid crystal cell, and at least one optical anisotropic element having a layer containing a liquid crystalline polymer between the liquid crystal cell and the polarizing element The optical tilt angle of the liquid crystalline polymer continuously changes in the thickness direction of the layer, and the direction in which the absolute value of the retardation value of the optical anisotropic element is minimized is the film method. The angle formed by the direction orthogonally projected on the liquid crystal cell substrate, not the line direction or the plane direction, and the rubbing direction of the liquid crystal cell substrate closer to the optical anisotropic element is 90 ° to 270 °. A characteristic liquid crystal display element.
(2) The liquid crystal display element according to (1), wherein the optical anisotropic element is a transparent film provided with a layer containing a liquid crystalline polymer.
(3) The liquid crystal display element according to claim 2, wherein the optical tilt angle of the liquid crystalline polymer monotonously increases continuously from the bottom surface in the thickness direction.
(4) The angle of the low tilt angle side of the continuously changing optical tilt angle of the liquid crystalline polymer is 0 ° to 85 °, and the angle of the high tilt angle side is 5 ° to 90 °. The liquid crystal display element according to (3), which is characterized.
(5) The transparent film is optically negative uniaxial, the optical axis is in the normal direction, the main refractive index in the film plane is nx, ny, the main refractive index in the thickness direction is nz, (4) The liquid crystal display element according to (4), wherein the retardation represented by formula 1 is 20 nm to 400 nm, where d is the thickness of the film.
(Formula 1) {(nx + ny) / 2−nz} × d
( 6 2) The two optically anisotropic elements are arranged so as to sandwich the liquid crystal cell, and the optically anisotropic elements are both orthogonally projected onto the liquid crystal cell substrate in the direction in which the absolute value of the retardation value is minimum, The angle formed by the rubbing direction of the liquid crystal cell substrate closer to the optical anisotropic element is 135 ° to 225 ° (2) to ( 5 ) Liquid crystal display element as described.
[0014]
The fact that the viewing angle has been improved to a higher degree in the liquid crystal display device of the present invention can be explained as follows.
For example, in the liquid crystal display device of the present invention, in the normally white mode in which the transmission axes of the polarizer and the analyzer are substantially orthogonal, the black display portion is in a state where a voltage is applied to the liquid crystal, and the viewing angle is increased. As a result, the transmittance of light from the black display portion is remarkably increased, resulting in a sharp decrease in contrast.
At this time, the arrangement of the liquid crystal molecules inside the TN type liquid crystal cell can be regarded as a continuous change from the state in which the optical axis is inclined from the normal direction of the cell to the state in which the normal direction is directed. .
[0015]
If the liquid crystal molecules inside the liquid crystal cell can be regarded as a positive uniaxial optical anisotropy, in order to compensate for the birefringence caused by this, a negative uniaxial molecule is similarly removed from the normal direction of the cell. It is necessary to use one that continuously changes from an inclined state to a state in which it faces the normal direction.
[0016]
However, regarding the optical anisotropy of a TN type liquid crystal cell as positive uniaxial, it is only an approximation. Actually, the liquid crystal cell is not a simple positive optical anisotropic body but is twisted and has a tilt angle. Has also changed. Therefore, it is naturally limited to compensate with a negative uniaxial optical anisotropic body having an inclined optical axis. As a result of intensive studies, the present inventor has further improved the viewing angle characteristics, and in order to open up the possibility of CRT substitution, the direction in which the retardation value becomes zero, that is, the optical axis does not exist, the retardation. It has been found that this can be realized by using an optical anisotropic element in which the direction in which the absolute value of the value is minimum is neither the film normal direction nor the plane direction. Further, as a specific method, the optical anisotropic element (A) in which the optical tilt angle of the liquid crystalline polymer continuously changes in the thickness direction of the layer, or at least the optical anisotropic element ( A) and an optically anisotropic element composed of an optically anisotropic element (B) that is optically negative uniaxial and has an optical axis in the normal direction. According to the present invention, not only contrast but also visual angle characteristics for gradation inversion can be greatly improved.
[0017]
When the liquid crystalline polymer layer of the present invention is regarded as a large number of laminates, each thin layer can be optically approximated as negative uniaxial. Furthermore, in the present invention, a thin-layer laminate that can approximate negative uniaxiality is defined as optically negative birefringence. The optical tilt angle of the liquid crystalline polymer layer as used herein refers to an angle formed by the (negative uniaxial) optical axis of the thin layer and a normal to the optical anisotropic element surface.
This solves the essential problem that the image quality deteriorates depending on the viewing angle due to the principle of the display method using a nematic liquid crystal with a twist angle of 90 °. In addition, problems such as color change have been improved.
[0018]
The optical anisotropic element in the present invention has a minimum value of the retardation value when viewed from all directions, and the direction is neither the film normal direction nor the plane direction. In addition, the minimum absolute value of retardation is not zero. In the present invention, at least one such optical anisotropic element is used.
[0019]
In the present invention, there is no direction in which the retardation value is zero, and an optical anisotropic element in which the absolute value of the retardation value is not the normal direction or the plane direction of the film is used. Compensation is made by arranging the angle α between the direction in which the direction having the smallest value is orthogonally projected on the liquid crystal cell substrate and the rubbing direction of the liquid crystal cell substrate closer to the optical anisotropic element in the range of 90 ° to 270 °. Performance is maximized. For example, an optical anisotropic element is arranged as shown in FIG. α is defined as shown in FIG. 2 when FIG. 1 is viewed from the origin in the z-axis direction. That is, the angle between the right direction from the rubbing direction of the liquid crystal cell substrate closer to the optical anisotropic element and the direction in which the absolute value of the retardation value of the optical anisotropic element is minimized. In the present invention, the main viewing angle direction is the average twist direction of the liquid crystal molecules in the liquid crystal cell. In FIG. 1, when a TN liquid crystal twisted 90 ° counterclockwise with the z axis as the rotation axis is used, −x Axial direction. The direction opposite to the main viewing angle direction is referred to as the anti-viewing angle direction.
[0020]
When one optical anisotropic element in which the absolute value of the retardation value is not the normal direction of the film or in the plane direction is used, the direction in which the absolute value of the retardation value is the smallest on the liquid crystal cell substrate It is preferable that the direction orthogonally projected on is the main viewing angle direction or the anti-viewing angle direction. This satisfies the condition of α being 90 ° to 270 °. As shown in FIG. 1, when such an optically anisotropic element is arranged on the upper side of the liquid crystal cell, the direction in which the absolute value of the retardation value is orthogonally projected onto the liquid crystal cell substrate is almost the main viewing angle direction. Preferably there is. In addition, when such an optically anisotropic element is disposed on the lower side of the liquid crystal cell, the direction in which the direction in which the absolute value of the retardation value is minimized is orthogonally projected onto the liquid crystal cell substrate is substantially the anti-viewing angle direction. preferable.
[0021]
Preferably, as shown in FIGS. 3 and 4, two such optical anisotropic elements are arranged so as to sandwich the liquid crystal cell, and each optical anisotropic element has a minimum absolute value of retardation value. The angle formed between the direction orthogonally projected on the liquid crystal cell substrate and the rubbing direction of the liquid crystal cell substrate closer to the optical anisotropic element is set to 135 ° to 225 °. More preferably, the angle β formed by orthogonally projecting the direction in which the absolute value of the retardation value of the two optical anisotropic elements defined in FIG. 4 is the minimum onto the liquid crystal cell substrate is 90 ° to 180 °. It is preferably in the range of °.
[0022]
The optical anisotropic element in the present invention will be described in detail below.
The liquid crystalline polymer layer in the present invention preferably has an optical tilt angle continuously changing in the thickness direction of the layer. When the liquid crystalline polymer layer is provided in the form of a transparent film, it is preferable that the optical tilt angle increases monotonously continuously from the bottom surface in the thickness direction. Furthermore, it is preferable that the low tilt angle side of the optical tilt angle of the liquid crystalline polymer layer is 0 ° to 85 °, and the high tilt angle side is 5 ° to 90 °.
[0023]
The liquid crystalline polymer layer is divided into thin layers that can be regarded as having uniform optical characteristics, and the sum of the retardations in the thickness direction of each thin layer is defined as the retardation of the liquid crystalline polymer layer. The retardation in the thickness direction of the thin layer means that the triaxial refractive index of the thin layer is n1, n2, n3 in order of increasing values, and the thickness of the thin layer is d.
{(N2 + n3) / 2−n1} × d
It is represented by The retardation of the liquid crystalline polymer layer is preferably 20 nm or more and 400 nm or less.
[0024]
The liquid crystalline polymer of the present invention preferably has a mesogenic group having a negative intrinsic birefringence value or exhibits a cholesteric phase.
Examples of the mesogenic group having a negative intrinsic birefringence value include C.I. Destrade et al., Mol. Cryst. 71, 111 (1981), benzene derivatives and B.I. Kohne et al., Angew. Chem. 96, page 70 (1984) and the cyclohexane derivatives described in J. Am. M.M. Lehn et al. Chem. Commun. , 1794 (1985), J. Am. Zhang et al., J. Am. Chem. Soc. 116, 2655 (1994), such as azacrown and phenylacetylene macrocycles, etc., which are generally used as a mother nucleus at the center of a molecule, and are a linear alkyl group or alkoxy group, substituted A structure in which a benzoyloxy group or the like is radially substituted as a straight chain thereof exhibits liquid crystallinity and includes what is generally called a discotic liquid crystal. However, the molecule itself is not limited to the above description as long as it has negative uniaxiality and can give a certain orientation.
The liquid crystalline polymers having a mesogenic group having a negative intrinsic birefringence value in the present invention are listed below.
[0025]
[Chemical 1]

[0026]
[Chemical formula 2]

[0027]
In addition, liquid crystalline polymers exhibiting a cholesteric phase in the present invention are listed below.
[0028]
[Chemical 3]

[0029]
[Formula 4]

[0030]
In the case of the present invention, in order to continuously change the optical tilt angle in the thickness direction, the following processing is required.
In general, in the case of a liquid crystal cell using nematic liquid crystal, the optical axes of liquid crystal molecules are aligned in a certain direction by sandwiching both sides of the liquid crystal layer with a rubbing-treated alignment film. In other words, the liquid crystal molecules are uniformly aligned in the thickness direction due to the alignment regulating force of the alignment film on both sides of the liquid crystal layer, and the alignment regulating force of the alignment film is unbalanced on both sides. The molecular orientation can be changed continuously in the thickness direction. This concept can also be applied to the liquid crystalline polymer of the present invention.
Specifically, a liquid crystalline polymer is applied to a substrate on which a rubbing-treated organic alignment film or inorganic alignment film is formed, and the temperature of the liquid crystal layer is raised to the liquid crystal phase formation temperature while leaving one side of the liquid crystal layer open (air layer). Alternatively, the temperature is raised to the liquid crystal phase formation temperature while being sandwiched between the alignment film and an alignment film subjected to a surface treatment different from the alignment film. However, when the alignment regulating force of the alignment film described above is sufficiently strong, the optical tilt angle of the liquid crystalline polymer can be maintained even if one side of the liquid crystalline polymer layer remains an open system (air layer). May be the same in the thickness direction.
[0031]
As a result, the liquid crystal has an oblique orientation in which the optical tilt angle continuously changes in the thickness direction, and takes a solid state at room temperature while maintaining the orientation by subsequent cooling. In this case, the tilt angle in the vicinity of the alignment film can be controlled by a liquid crystalline polymer material, an alignment film material, rubbing, etc., and the tilt angle is preferably 0 ° to 85 °, preferably 0 ° to 50 ° is more preferable.
In addition, the tilt angle in the vicinity of the air layer or the alignment film subjected to different surface treatments can be controlled by a liquid crystalline polymer material, a plasticizer, a binder, a surfactant, etc. The degree of orientation change in the thickness direction of the tilt angle can be controlled with these plasticizers, binders, surfactants, and the like.
[0032]
Preferred examples of these plasticizers are not particularly limited as long as they are compatible with the liquid crystalline polymer to be used. From the viewpoint of imparting heat resistance, it is preferable to have a reactive substituent. Further, the addition amount with respect to the liquid crystalline polymer is preferably 0.1 wt% to 50 wt% in weight ratio.
Further, as a preferable example of the binder, there is no particular limitation as long as it does not significantly inhibit the alignment of the liquid crystalline polymer to be used, and a commercially available polymer can be used. As a result of diligent research by the present inventors, it has been found that in the case of a liquid crystalline polymer having a discotic liquid crystal as a mesogenic group, a cellulose polymer derivative is extremely preferable.
[0033]
The liquid crystal phase formation temperature is specific to the structure, molecular weight, etc., but can be arbitrarily adjusted by mixing two or more different types or by mixing the above-mentioned plasticizers.
The liquid crystal phase-solid phase transition temperature of the liquid crystalline polymer used in the present invention is preferably 70 ° C. or higher and 300 ° C. or lower, particularly preferably 70 ° C. or higher and 250 ° C. or lower.
[0034]
Examples of the polymer used as the organic alignment film include polyimide and polystyrene derivatives, and examples of water-soluble polymers include gelatin, polyvinyl alcohol, and carboxymethyl cellulose. All of these can be obliquely oriented by applying a rubbing treatment.
[0035]
A polyimide film widely used as an alignment film for LCD is preferable as an organic alignment film, and this is applied to a substrate surface with polyamic acid (for example, LQ / LX series manufactured by Hitachi Chemical Co., Ltd., SE series manufactured by Nissan Chemical Co., Ltd.). It is obtained by rubbing after baking at a temperature of 0.5 to 1 hour.
[0036]
The rubbing process is the same as a process widely used as a liquid crystal alignment process for LCD, and the surface of the alignment film is fixed using paper, gauze, felt, rubber, nylon, polyester fiber or the like. This is a method of obtaining orientation by rubbing in the direction. In general, rubbing is performed several times using a cloth in which fibers having a uniform length and thickness are flocked on average.
[0037]
In addition, as a deposition material of the inorganic oblique deposition film, SiO is representative and TiO is representative. ₂ , MgF ₂ ZnO ₂ And metal oxides such as fluorides, metals such as Au and Al. In addition, if a metal oxide is a thing with a high dielectric constant, it can be used as an oblique vapor deposition substance, It is not limited to the above.
[0038]
As the optically anisotropic element (B) constituting the optically anisotropic element of the present invention and having an optically negative uniaxial property and its optical axis being in the normal direction of the film, the light transmittance is 80% or more. At the same time, when the main refractive index in the film plane is nx, ny, the main refractive index in the thickness direction is nz, and the thickness of the film is d, the relationship between the triaxial main refractive indexes satisfies nz <ny = nx, The retardation represented by the formula {(nx + ny) / 2-nz} × d is preferably 20 nm to 400 nm, and more preferably 20 nm to 150 nm.
However, the values of nx and ny do not have to be strictly equal, and it is sufficient if they are almost equal. Specifically, if | nx−ny | / | nx−nz | ≦ 0.3, there is no practical problem. The front retardation represented by | nx−ny | × d is preferably 50 nm or less, and more preferably 20 nm or less.
[0039]
The optical anisotropic element (B) is made of a material having a low intrinsic birefringence, such as ZEONEX (Nippon ZEON), ARTON (Nippon Synthetic Rubber), or Fujitac (Fuji Photo Film), or a polycarbonate, A material having a large intrinsic birefringence, such as polyarylate, polysulfone, or polyethersulfone, can be formed by forming a film by solution casting, melt extrusion, or the like.
[0040]
Since the optical anisotropic element of the present invention compensates for birefringence due to the liquid crystal cell in the liquid crystal display element, the wavelength dispersion of the optical anisotropic element is preferably equal to that of the liquid crystal cell. That is, if the retardation of the optically anisotropic element with light of 450 and 550 μm is R450 and R550, respectively, the R450 / R550 value representing wavelength dispersion is preferably 1.0 or more.
[0041]
When the liquid crystal display element of the present invention is used as a color liquid crystal display device, a color filter is required. As color filters used at that time, for example, Kobayashi Keisuke edited by “Color Liquid Crystal Display” Industrial Books, pages 172 to 173, pages 237 to 251, or Nikkei Microdevices “Flat Panel Display 1994” Nikkei BP, page 216 After adding a dichromate to a substrate such as gelatin, casein, or PVA described in the above, the photolithographic method is used for patterning, and then dyeing, printing, and electrodeposition are obtained. A filter or a pigment dispersion filter is preferred.
However, other than this, any one having high color purity, dimensional accuracy, and high heat resistance can be used regardless of the method.
[0042]
As the liquid crystal used in the liquid crystal display device of the present invention, for example, nematic liquid crystal described in pages 107 to 213 of the “Liquid Crystal Device Handbook” edited by the Japan Society for the Promotion of Science, 1st and 2nd Committee, Nikkan Kogyo Shimbun, is preferable. The major axis of this liquid crystal molecule is twisted by approximately 90 ° between the upper and lower substrates of the liquid crystal cell. When there is no applied electric field, the incident linearly polarized light changes the 90 ° polarization direction depending on the optical rotation of the liquid crystal cell. The light is emitted from the liquid crystal cell. When a sufficiently high electric field exceeding the threshold value is applied, the major axis of the liquid crystal molecules changes in the direction of the electric field and is perpendicular to the electrode surface, so that the optical rotation almost disappears. Therefore, in order to fully demonstrate the effect of this optical rotation In addition, Twist angle is 70 ° -100 ° And 80 ° to 90 ° is more preferable.
[0043]
In order to reduce the alignment defect (disclination) of the liquid crystal molecules due to the electric field, it is preferable to give a pretilt angle to the liquid crystal molecules in advance. The pretilt angle is preferably 5 ° or less, and more preferably 2 ° to 4 °.
The twist angle and the pretilt angle are described in “Liquid Crystal Application” Baifukan, pages 16 to 28, edited by Koji Okano and Keisuke Kobayashi.
[0044]
Further, the value of the product Δnd of the refractive index anisotropy Δn of the liquid crystal cell and the thickness d of the liquid crystal layer in the liquid crystal cell is, for example, “Liquid Crystal Device Handbook” edited by Japan Society for the Promotion of Science 142nd page, page 329. As described on page 337, the contrast is improved if d is increased, but the response speed is slow and the viewing angle is also deteriorated. Therefore, the range of 300 nm to 1000 nm is preferable, and the range of 300 nm to 600 nm is preferable. More preferred.
[0045]
The signal applied to the liquid crystal display device of the present invention is, for example, “Liquid Crystal Device Handbook” edited by Japan Society for the Promotion of Science 142nd page, Nikkan Kogyo Shimbun, pages 387 to 465, or Mitsuji Okano and Keisuke Kobayashi “Liquid Crystal Application”. "As described in Baifukan, pages 85-105, etc., the voltage is 20 V or less, preferably 8 V or less, with an alternating current of 5 Hz to 100 Hz. For example, in the normally white mode, bright display is often performed when the applied voltage is 0 to 1.5V, halftone display is performed when the applied voltage is 1.5V to 3.0V, and dark display is often performed when the applied voltage is 3.0V or higher.
[0046]
In the present invention, when a layer containing a liquid crystalline polymer is provided on a transparent film, the liquid crystalline polymer layer is disposed closer to the liquid crystal cell when the optical anisotropic element is mounted on the liquid crystal cell, and the transparent film Although it may arrange | position near a liquid crystal cell, in this invention, you may arrange | position in any. However, in order to maximize the compensation capability, it is preferable to dispose the liquid crystalline polymer layer closer to the liquid crystal cell.
[0047]
【Example】
Hereinafter, the present invention will be described in detail based on examples.
[0048]
Example 1
A long-chain alkyl-modified poval (MP203: manufactured by Kuraray Co., Ltd.) was applied to a triacetylcellulose 100 μm thick film (Fuji Photo Film Co., Ltd.) coated with a gelatin thin film (0.1 μm), and warm air at 40 ° C. After drying, the film was rubbed to form an alignment film. When the in-plane main refractive index is nx ', ny', the refractive index in the thickness direction is nz ', and the thickness is d', the triacetyl cellulose film is | nx'-ny '| xd' = 3 nm. {(Nx ′ + ny ′) / 2−nz ′} × d ′ = 70 nm, almost negative uniaxiality, and the optical axis was substantially in the film normal direction.
[0049]
On this alignment film, 1.6 g of the aforementioned liquid crystalline polymer TE-6, phenol EO-modified (n = 1) acrylate (M101 Toa Gosei) 0.4 g, cellulose acetate butyrate (CAB531-1) (Eastman Chemical) A coating solution prepared by dissolving 0.05 g of Irgacure 907 0.01 g in 3.65 g of methyl ethyl ketone was applied with a wire bar (using # 4 bar), and attached to a metal frame. After heating for 3 minutes in a high-temperature bath at 115 ° C. to align the liquid crystal, it was rapidly cooled to room temperature to produce an optical anisotropic element having a layer containing a liquid crystalline polymer.
[0050]
The retardation of the optically anisotropic element obtained in this way is obtained by Shimadzu Corp. in increments of 5 ° from 40 ° to 140 ° starting from the rubbing axis on the surface perpendicular to the retardation plate surface including the rubbing axis. When measured using an ellipsometer (AEP-100), there was no direction in which the retardation was zero. The direction in which the absolute value of the retardation value was minimized was neither the film normal direction nor the plane direction. In addition, on the surface that includes the rubbing axis and is perpendicular to the phase difference plate surface, the measurement value is measured in increments of 5 ° from 40 ° to 140 ° starting from the rubbing axis. The optical properties of the support after removing the molecules were measured in the same manner. Further, when the liquid crystalline polymer layer was divided into 10 in the thickness direction and the measured values were simulated, the tilt angle of the liquid crystalline polymer layer was continuously changed from 20 ° to 70 °. The retardation was 70 nm.
[0051]
The product of the refractive index difference between liquid crystal extraordinary light and ordinary light and the gap size of the liquid crystal cell is 420 nm and the twist angle is 90 degrees. One optical anisotropic element is shown in FIG. It was attached so that it might become the same arrangement. The mounting angle of each optical element is as shown in FIG. The angle α between the direction in which the direction in which the absolute value of the retardation value of the optical anisotropic element is minimum is orthogonally projected onto the liquid crystal cell substrate and the rubbing direction of the liquid crystal cell substrate closer to the optical anisotropic element is 225 °. It was.
[0052]
Example 2
With the configuration as shown in FIG. 3, two optical anisotropic elements used in Example 1 were placed in the same TN liquid crystal cell as in Example 1 so as to sandwich the liquid crystal cell. The mounting angle of each optical element is as shown in FIG. α1 was 180 ° and α2 was 180 °.
[0053]
Comparative Example 1
The same TN type liquid crystal cell as in Example 1 was arranged as shown in FIG. 7 without mounting an optical anisotropic element.
[0054]
Comparative Example 2
With the configuration as shown in FIG. 3, two optical anisotropic elements used in Example 1 were placed in the same TN liquid crystal cell as in Example 1 so as to sandwich the liquid crystal cell. The mounting angle of each optical element is as shown in FIG. α1 was 0 ° and α2 was 0 °.
[0055]
Example 3
A polyimide layer was formed on a 60 μm PC film and rubbed to form an alignment film. When the main refractive index in the plane is nx ', ny', the refractive index in the thickness direction is nz ', and the thickness is d', the PC film is | nx'-ny '| xd' = 5 nm, { (Nx ′ + ny ′) / 2−nz ′} × d ′ = 100 nm, almost negative uniaxiality, and the optical axis was substantially in the film normal direction.
On this alignment film, methylene chloride was added to the liquid crystalline polymer TE-7 described above to make a 20 wt% solution as a whole, and coating was performed at 2000 rpm by a spin coat. After heating to 85 ° C. and heat treatment, it was rapidly cooled to room temperature to form a liquid crystal layer of approximately 0.5 μm, and an optical anisotropic element was produced.
When the same optical measurement as in Example 1 was performed and the optical tilt angle of the liquid crystalline polymer layer was simulated, it changed from 15 ° to 35 °, and the retardation was 80 nm.
[0056]
As a protective film on the liquid crystal cell side, a direct optical anisotropic element and a liquid crystalline polymer layer were bonded to the polarizing film prepared by adsorbing iodine to the stretched PVA. Then, with the configuration as shown in FIG. 3, two TN liquid crystal cells as in Example 1 were arranged so as to sandwich the liquid crystal cell. The mounting angle of each optical element is as shown in FIG. α1 was 180 ° and α2 was 180 °.
[0057]
(Viewing angle measurement)
A voltage was applied to the liquid crystal cell with a 55 Hz rectangular wave. Otsuka Electronics makes contrast ratio measurements from the front and up / down and left / right tilt directions, with the ratio of white display 1V and black display 5V (white display) / (black display) as the contrast ratio. Performed on LCD-5000. Table 1 shows the front contrast and the upper / lower and left / right viewing angles at which contrast is 10 or more and gradation inversion does not occur.
[0058]
[Table 1]

[0059]
As is apparent from Table 1, the optical anisotropic element of the present invention can widen the viewing angle without lowering the front contrast.
[0060]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the viewing angle characteristic of TN type | mold liquid crystal display element can be improved, and the liquid crystal display element of a high quality display which is excellent in visibility can be provided. Further, it goes without saying that excellent effects can be obtained even when the present invention is applied to an active matrix liquid crystal display element using three-terminal and two-terminal elements such as TFT and MIM.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining one embodiment of a configuration of a liquid crystal display element of the present invention.
2 is a diagram for explaining an axis configuration when FIG. 1 is viewed in the z-axis direction from the origin. FIG.
FIG. 3 is a diagram for explaining one embodiment of the configuration of the liquid crystal display element of the present invention.
FIG. 4 is a diagram illustrating an axis configuration when FIG. 3 is viewed from the origin in the z-axis direction.
FIG. 5 is a diagram illustrating a shaft configuration according to the first embodiment.
FIG. 6 is a diagram illustrating a shaft configuration according to the second embodiment.
FIG. 7 is a diagram illustrating a shaft configuration of Comparative Example 1
FIG. 8 is a diagram for explaining a shaft configuration of Comparative Example 2;
FIG. 9 is a view for explaining a shaft configuration of the third embodiment.

Claims (6)

A TN type liquid crystal cell in which a liquid crystal having a twist angle of 70 ° to 100 ° is sandwiched between two electrode substrates, two polarizing elements disposed on both sides thereof, and between the liquid crystal cell and the polarizing element A liquid crystal display element in which at least one optical anisotropic element having a layer containing a liquid crystalline polymer is disposed, wherein the optical tilt angle of the liquid crystalline polymer continuously changes in the thickness direction of the layer. The direction in which the absolute value of the retardation value of the optically anisotropic element is minimum is neither the film normal direction nor the plane direction, and the direction orthogonally projected on the liquid crystal cell substrate and the optically anisotropic An angle formed by a rubbing direction of a liquid crystal cell substrate closer to the element is 90 ° to 270 °. The liquid crystal display element according to claim 1, wherein the optically anisotropic element is a transparent film provided with a layer containing a liquid crystalline polymer. 3. The liquid crystal display element according to claim 2, wherein the optical tilt angle of the liquid crystalline polymer monotonously increases continuously from the bottom surface in the thickness direction. The low tilt angle side of the continuously changing optical tilt angle of the liquid crystalline polymer is 0 ° to 85 °, and the high tilt angle side angle is 5 ° to 90 °. The liquid crystal display element according to claim 3. The transparent film is optically negative uniaxial, the optical axis is in the normal direction, the main refractive index in the film plane is nx, ny, the main refractive index in the thickness direction is nz, and the thickness of the film The liquid crystal display element according to claim 4, wherein when d is d, the retardation represented by Formula 1 is 20 nm to 400 nm.
(Formula 1) {(nx + ny) / 2−nz} × d The two optically anisotropic elements are arranged so as to sandwich the liquid crystal cell, and both the optically anisotropic elements are orthogonally projected onto the liquid crystal cell substrate in the direction in which the absolute value of the retardation value is minimum, and the optical the liquid crystal display device of claims 2 to 5, wherein the angle between the rubbing direction of the liquid crystal cell substrate closest to the anisotropic element is 135 ° to 225 °.

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