JP3568449B2

JP3568449B2 - Liquid crystal display

Info

Publication number: JP3568449B2
Application number: JP2000076252A
Authority: JP
Inventors: 剛須崎; 裕之賀勢; 善隆森; 慎一郎田中
Original assignee: Tottori Sanyo Electric Co Ltd; Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 2000-03-17
Filing date: 2000-03-17
Publication date: 2004-09-22
Anticipated expiration: 2020-03-17
Also published as: JP2001264764A

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device having excellent viewing angle characteristics. SOLUTION: In the liquid crystal display device having a liquid crystal layer 3 held between a pair of substrates 1, 2, the liquid crystal layer 3 has a region 12a where the liquid crystal molecules 4 are aligned horizontally along the normal direction 9 of the substrates 1, 2 and a region 12b where the liquid crystal molecules 4 are aligned perpendicularly. The gap widths dh, dv of the regions 12a, 12b, respectively, are determined in such a manner that when the device is observed in the direction inclined from the normal direction 9 of the substrates 1, 2, the retardation by the liquid crystal molecules 4 in the region 12a having the horizontal arrangement and the retardation by the liquid crystal molecules 4 in the region 12b having perpendicular arrangement are compensated with each other.

Description

【０００１】
【発明の属する技術分野】
本発明は、高速応答性及び視角特性に優れた液晶表示装置に関する。
【０００２】
【従来の技術】
液晶表示装置は薄型軽量、低消費電力という特徴があり、携帯端末からパーソナルコンピュータ、テレビに至るまで幅広く利用されている。こうした液晶表示装置にはその性能として高速応答や広視野角が要求され、その要求を満たすために様々な工夫がなされている。高速応答が可能な液晶表示装置として、例えば特開平９−１４６０８６号公報や特開平９−１９７３９７号公報に開示されているＨＡＮ配向（ｈｙｂｒｉｄＡｌｉｇｎｅｄＮｅｍａｔｉｃ）の液晶表示装置がある。
【０００３】
この従来の液晶表示装置を図７及び図８に基づき説明する。ここではオフ時に黒表示となるノーマリブラックの場合を説明する。図７は黒表示（オフ時）における液晶表示装置の概略構成図であり、図８は黒表示（オフ時）における偏光板の透過軸と液晶分子を配列状態との位置関係を示す概略図である。
【０００４】
この液晶表示装置は一方の基板１００ｂには水平配向処理を行い、他方の基板１００ａには垂直配向処理を行ったもので、オフ状態の場合は、液晶分子１０２は水平配向の基板１００ｂ側では所定のプレチルト角を有して水平配列し、垂直配向の基板１００ａ側では垂直配列し、その間の液晶層１０１で水平配列から垂直配列に徐々に配列状態を変化している。
【０００５】
この液晶層１０１を挟んだ基板１００の上下には偏光板１０３が配置され、この偏光板１０３は、両偏光板１０３の透過軸１０７のなす角が９０度で、水平配向の基板１００ｂに対応する偏光板１０３ｂの透過軸１０７ｂが水平配向の配向方向と４５度をなすように設定されている。なお、透過軸を吸収軸に置換えても良い。図８では基板１００ｂ側の液晶分子１０２ｂ及び偏光板１０３ｂの透過軸１０７ｂを点線で示し、基板１００ａ側の液晶分子１０２ａ及び偏光板１０３ａの透過軸１０７ａを実線で示している。
【０００６】
基板１００ａと偏光板１０３ａの間には光学補償シート１０８を設けている。この光学補償シート１０８は、オフ時の液晶層１０１と光学補償シート１０８の合成屈折率楕円体が球になるような屈折率楕円体を有し、例えば１軸性又は２軸性の光学異方素子が用いられる。
【０００７】
そして透過軸１０７ｂを通過した入射光（直線偏光）は液晶層１０１の液晶分子１０２、光学補償シート１０８を通過して偏光板１０３ａへ達する。このオフ時には液晶層１０１と光学補償シート１０８の合成屈折率楕円体が球になるので、偏光板１０３ａに達した透過光は振幅方向が透過軸１０７ｂと同一方向の直線偏光になり、偏光板１０３ａの透過軸１０７ａを通過することなく黒表示（ノーマリブラックモード）になる。
【０００８】
また液晶層１０１に所定電圧が印加されると、水平配列している液晶分子１０２の配列状態が垂直配列に変化し、液晶層１０１と光学補償シート１０８の合成屈折率楕円体が球から楕円体に変化する。したがって透過軸１０７ｂを通過した入射光（直線偏光）は、偏光板１０３ａに達したときに液晶層１０１と光学補償シート１０８による複屈折効果により楕円偏光になるので、透過軸１０７ａを通過して白表示になる。
【０００９】
【発明が解決しようとする課題】
しかしＨＡＮ配向の液晶表示装置は、偏光板１０３ａの表面の法線方向から見たときは良好な黒表示が実現できるが、法線方向に対してある程度の角度をなす方向から見たときに光漏れが生じる。特に透過軸１０７の方向１０９から偏光板１０３ａを斜めに見る場合は光漏れが少ないものの、透過軸１０７と４５度の角度をなす方向１１０から偏光板１０３ａを斜めに見る場合は光漏れが多い。
【００１０】
こうした光漏れを防ぐために、どの方向から偏光板１０３ａを斜めに見た場合も液晶層１０１と光学補償シート１０８の合成屈折率楕円体が球になるように、光学補償シートに様々な工夫することが試みられている。
【００１１】
そこで本発明は、液晶層の垂直配列の液晶分子と水平配列の液晶分子が互いのリタデーションを相殺するようにして液晶層自体に視角補償の機能を持たせ、広視角化及び高速応答が可能な液晶表示装置を提供することを目的とする。
【００１２】
【課題を解決するための手段】
上記課題を解決するために請求項１記載の発明は、一対の基板間に液晶層を挟み込んだ液晶表示装置において、液晶層は基板の法線方向について液晶分子が水平配列した領域と垂直配列した領域を有し、水平配列した領域の液晶分子によるリタデーションと垂直配列した領域の液晶分子によるリタデーションが互いに相殺し合うように各領域のギャップ幅を設定したことを特徴とする。
【００１３】
また請求項２記載の発明は、一対の基板間に液晶層を挟み込み、一方の基板の配向膜には垂直配向を行い、他方の基板の配向膜には水平配向を行った液晶表示装置において、垂直配向の配向膜に影響されて垂直配列する液晶分子のリタデーションと水平配向の配向膜に影響されて水平配列する液晶分子のリタデーションとが相殺するように各配向膜の配向アンカリングの強度を設定したことを特徴とする。
【００１４】
また請求項３記載の発明は、一対の基板を一対の偏光板で挟んだ液晶表示装置において、両偏光板の透過軸又は吸収軸のなす角度が９０度になると共に、水平配向の配向膜を有する基板に対応する偏光板の透過軸又は吸収軸が水平配向方向と同一方向になるように偏光板が配置されていることを特徴とする。
【００１５】
また請求項４記載の発明は、偏光板の透過軸又は吸収軸に対して４０度から５０度をなす方向であって、且つ偏光板の法線方向に対して１０度から７０度の方向に含まれる所定の方向から偏光板を見たときの液晶層のリタデーションがほぼ０になるように、水平配列の領域と垂直配列の領域のギャップ幅を設定したことを特徴とする。
【００１６】
また請求項５記載の発明は、基板間にカイラル剤が添加された誘電率異方性が負のネマティック液晶を介在させたことを特徴とする。
【００１７】
また請求項６記載の発明は、一対の基板のうち、一方の基板の配向膜には水平配向が施され、他方の基板の配向膜には垂直配向が施されると共に一方の基板の配向膜に施された水平配向方向と直交する水平方向に配向処理が施されていることを特徴とする。
【００１８】
【発明の実施の形態】
以下、本発明の実施の形態を図に基づいて説明する。この液晶表示装置はノーマリブラックモードであり、図１は黒表示（オフ時）における液晶分子の配列状態を示す概略構成図、図２は白表示（オン時）における液晶分子の配列状態を示す概略構成図、図３はオフ時の液晶表示装置の側面該略図、図４は偏光板の透過軸と液晶分子の配列方向の関係を示す図である。
【００１９】
第１基板１はガラス基板１ａ上に画素電極１ｂ、配向膜１ｃを積層し、第２基板２はガラス基板２ａ上に透明電極２ｂ、配向膜２ｃを積層している。第１基板１上にスペーサを散布させた後、第１基板１と第２基板２をそれぞれの配向膜１ｃ、２ｃが向かい合うように所定の位置に対向配置し、両基板１、２の周辺をシール剤で固着する。両基板１、２間に誘電率異方性が負のネマティック液晶３が封入され、液晶分子４が配向膜１ｃ、２ｃの影響によって後述する配列を保っている。また液晶層３にはカイラル剤が添加されているので、オン時には図２に示すように液晶分子４が配列する。なおこの実施例では、カイラル剤は液晶分子４を右方向（時計回り）に回転させる特性を有している。
【００２０】
第１基板１の下方には下偏光板５が配置され、第２基板２の上方には上偏光板６が配置されている。下偏光板５と上偏光板６は図４に示すように、その表面の法線方向９から見た際に互いの透過軸８ａ、８ｂが直交するように配置され、且つ下偏光板５は透過軸８ａと第１基板１の配向方向７ａが同一方向になるように配置される。図４では第１基板１側の液晶分子４ａ及び下偏光板５の透過軸７ａを実線で示し、第２基板２側の液晶分子４ａ及び上偏光板６の透過軸７ｂを点線で示している。また、両基板１、２及び両偏光板５、６は表面が平行になるように配置されるので、その法線方向９は一致する。なお、この実施例では透過軸で説明するが、透過軸の代わりに吸収軸の場合でもよい。
【００２１】
第１基板１の配向膜１ｃには水平配向処理が施され、第２基板２の配向膜２ｃには垂直配向処理が施されている。また第２基板２の配向膜２ｃには第１基板１ｃの水平配向の配向方向７ａと９０度をなす方向７ｂに配向処理が行われ、オン時に第２基板２側の液晶分子４ｂがその配向方向７ｂに配列する。この配向処理は、第２基板２に垂直配向膜を積層し、この垂直配向膜に形成しようとする配向方向７ｂと振幅方向が直交する直線偏光の紫外線を照射することで、オフ時には垂直配向が液晶分子４に作用しながらオン時には液晶分子４を配向方向７ｂの水平方向に配列するよう作用する配向膜２ｃが形成できる。
【００２２】
オフ時（図１）には、第１基板１側の液晶分子４ａは配向膜１ｃの水平配向に影響されてプレチルト角θの傾斜で水平配列し、第２基板２側の液晶分子４ｂは配向膜２ｃの垂直配向に影響されて垂直配列する。このとき液晶分子４の水平配列領域１２ａのギャップ幅と垂直配列領域１２ｂのギャップ幅は、上偏光板６の法線方向９に対してある角度を有する斜め方向から見たときに光り漏れが生じないように、水平配列領域１２ａのリタデーションと垂直配列領域１２ｂのリタデーションが相殺するように設定され、これは各配向膜１ｃ、２ｃの配向アンカリングの強さを調整して実現する。特に透過軸８ａ、８ｂに対して４５度の角度（β）をなす方向から見た際の液晶層３のリタデーションがほぼ０になるように設定すれば、オフ時の光漏れを最小限に抑えることができる。
【００２３】
そしてオフ時の場合、振幅方向が透過軸８ａと同一方向の直線偏光（入射光）１０ａが下偏光板５を通過し、液晶分子４を介して上偏光板６へ到達する。このとき上偏光板６へ達した透過光１０ｂは入射光１０ａと振幅方向が同一方向の直線偏光なので、上偏光板６によって遮られる。また、水平配列領域１２ａの液晶分子４ａが透過光１０ｂに与えるリタデーションと垂直配列領域１２ｂの液晶分子１０ａが透過光１０ｂに与えるリタデーションが相殺し合うので、例えば透過軸８ｂと４５度（β）をなす方向から斜めに見た場合（矢印１）も黒表示になる。
【００２４】
オン時（図２）の場合、誘電率異方性が負の液晶にカイラル剤が添加されているので、垂直配列状態の液晶分子４ｂは水平方向に倒れ、且つ水平状態の液晶分子４は右方向（時計回り）へ回転する。したがって液晶層３では第１基板１から第２基板２にかけて液晶分子４が時計回りに捻れながら配列する。さらに垂直配向処理が施された配向膜２ｃには、配向膜１ｃの配向方向７ａと直交する水平方向７ｂの配向処理が施されているので、垂直配列状態１２ｂの液晶分子４ｂが第２基板２の配向方向７ｂに水平配列し、第１基板１側の液晶分子４ａの長軸方向と第２基板２側の液晶分子４ｂの長軸方向が９０度になるように捻れながら配列する。なおこの実施例では、液晶層３内で液晶分子４が９０度捻れるように液晶層３のギャップ幅やカイラル剤を設定している。
【００２５】
そして下偏光板５を通過した直線偏光の入射光１０ａは液晶分子４によって旋光されて上偏光板６へ達する。上偏光板６へ達した透過光１０ｃはその振幅方向が透過軸８ｂと同一方向の直線偏光になっているので、上偏光板６を通過して白表示になる。
【００２６】
このようにノーマリブラックモードのＨＡＮ配向の液晶表示装置において、オン時に液晶分子４を水平配列状態で捻れるようにしているので、光学補償シート等を設けなくても簡単な構成で白表示が実現できる。
【００２７】
次に水平配列領域のギャップ幅と垂直配列領域のギャップ幅の一例を説明する。図５は図４のＡ’−Ａ’線に沿った側面概略図であり、説明及び計算を簡単にするために液晶層３を垂直配列領域１２ｂと水平配列領域１２ａの２つに領域に分割し、垂直配列領域１２ｂの液晶分子４ｂは全て基板の法線方向９と平行に垂直配列し、水平配列領域１２ａの液晶分子４ａは全て基板の法線方向９と直交方向に水平配列するものとする。そしてこの例では、透過軸８ｂと４５°（β）をなす方向で且つ基板の法線方向９に対して７０°（α）の方向から液晶層３を見たときのリタデーションがほぼ０になるように設定する。
【００２８】
液晶分子４の屈折率は長軸方向ｎ_ｘ＝１．５５７５、短軸方向ｎ_ｙ＝１．４７５４とし、液晶層３のギャップ幅は垂直配列領域１２ｂがｄ_ｖ、水平配列領域１２ａがｄ_ｈとする。
【００２９】
α＝７０°の場合、液晶層３における光の進行方向α’は約３８°になる（図５）。また、液晶層３における光の進行方向と液晶分子４ａの長軸とのなす角度γ_１は約６４°になり、屈折率が最大となる光の振動方向（以下、振動方向１という）と液晶分子の長軸とのなす角γ_２はγ_２＝９０°−γ_１＝２６°になる。
【００３０】
ここで図６にα、γ_１、γ_２等の関係を示す。図６において液晶分子４ａの長軸はＸ軸上にあるものとし、Ｚ軸の正領域が空気中、負領域が液晶層とする。またＸＹ平面のＡ’−Ａ’線は、光路（矢印１）をＸＹ平面に投影したときの線を示す。ここでＺ軸の正領域においてＺ軸とα、Ｙ軸とβをなす方向（光路）から原点を見ると、Ｚ軸の負領域（液晶層）においてＺ軸とα’、Ｙ軸と４５°をなす方向へ光路を得る。このときのＺ軸の負領域における光路とＸ軸（液晶分子の長軸）とのなす角がγ_１となり、この光路と直交しＸ軸と交差する線とＸ軸がなす角がγ_２となる。なお振動方向１は、振動成分が光路と直交し且つ振動成分方向とＸ軸（液晶分子の長軸方向）とが９０°をなす光（常光）に対し、振動成分が光路及び常光と直交し且つＸ軸と交差する方向になる。
【００３１】
次にα＝７０°、β＝４５°のときの水平配列領域１２ａにおけるリタデーションＲ（ｈ、α）を計算する。このときの水平配向領域１２ａにおける振動方向１に対する屈折率ｎ_ｘｈ（α）は次式で表される。
【００３２】
ｎ_ｘｈ（α）＝ｎ_ｘ・ｎ_ｙ／（ｎ_ｘ ^２・ｓｉｎ^２γ_２＋ｎ_ｙ ^２・ｃｏｓ^２γ_２）^０．５
また常光屈折率ｎ_ｙｈ（α）はｎ_ｙｈ（α）＝ｎ_ｙ、水平配列領域における光路ｄ（ｈ、α）はｄ（ｈ、α）＝ｄ_ｈ／ｃｏｓα’で表せる。したがって水平配列領域１２ａにおけるリタデーションＲ（ｈ、α）は次式で表せる。
【００３３】

更にα＝７０°、β＝４５°のときの垂直配列領域１２ｂにおけるリタデーションＲ（ｖ、α）を計算する。このときの垂直配向領域１２ｂにおける異常光屈折率ｎ_ｘｖ（α）は次式で表される。
【００３４】
ｎ_ｘｖ（α）＝ｎ_ｘ・ｎ_ｙ／（ｎ_ｘ ^２・ｃｏｓ^２α’＋ｎ_ｙ ^２・ｓｉｎ^２α’）^０．５
また常光屈折率ｎ_ｙｖ（α）はｎ_ｙｖ（α）＝ｎ_ｙ、垂直配列領域１２ｂにおける光路ｄ（ｖ、α）はｄ（ｖ、α）＝ｄ_ｖ／ｃｏｓα’で表せる。したがって垂直配列領域１２ｂにおけるリタデーションＲ（ｖ、α）は次式で表せる。

ここでα＝７０°、β＝４５°の方向から見たときの投影された垂直配列の液晶分子４ｂの長軸方向と投影された水平配列の液晶分子４ａの長軸方向がなす角度γ_３は約５２°になるので、液晶層のトータルのリタデーションＲ（α、β）は近似的に次式で表される。
【００３５】

そしてＲ（α、β）＝０のときは、ｄ_ｈ＝２．７１４ｄ_ｖの関係が成り立つ。ここで液晶層全体のギャップ幅が５〜６μｍの場合は、ｄ_ｖ＝１５８０ｎｍ、ｄ_ｈ＝４２８９ｎｍに設定すればα＝７０°、β＝４５°の方向から見たときのリタデーションＲ（α、β）がほぼ０になり、この方向の視角依存性の小さい液晶表示装置が実現できる。なお、このときΔｎ・ｄ_ｖ＝１３０、Δｎ・ｄ_ｈ＝３５２になる。
【００３６】
こうして求めたギャップ幅ｄ_ｖ、ｄ_ｈになるように配向膜１ｃ、２ｃの配向アンカリングの強度を設定する。ここで求めたギャップ幅ｄ_ｖ、ｄ_ｈは液晶層３の液晶分子４が図５に示すように配列している場合の値である。しかし水平配列している液晶分子４ａはプレチルト角θで傾斜し、第１基板１から第２基板２までの液晶分子４は水平配列から垂直配列へ徐々に配列状態が変わっている。したがって求めたギャップ幅ｄ_ｖ、ｄ_ｈに設定した後で実験等により各ギャップ幅を適正値に調整することで、黒表示のときに光漏れが少なくコントラストを改善した液晶表示装置になる。
【００３７】
また、配向アンカリングの強度を求めたギャップ幅ｄ_ｖ、ｄ_ｈの条件を満たす範囲でできるだけ強くすれば、水平配列領域１２ａと垂直配列領域１２ｂの占める範囲が多くなり、水平配列から垂直配列に配列状態が変わる液晶分子４の領域を少なくすることができる。こうすれば液晶分子４の配列状態が図５に示す配列状態に近くなり、ギャップ幅ｄ_ｖ、ｄ_ｈの計算値が有効に活用できる。更に、こうして各ギャップ幅を設定した液晶表示装置に光学補償シートを追加すれば、更に視角依存性をなくすことができ、視角特性を向上させることができる。
【００３８】
この実施例ではα＝７０°、β＝４５°の場合を説明したが、本発明はこの方向に限定するものではなく、他の方向から斜めに上偏光板６を見たときに液晶層３のリタデーションがほぼ０になるように設定してもよい。ただしβ＝４５°の方向からの見たときが光漏れが多いので、βが４０度から５０度且つαが１０度から７０度に含まれる範囲のうちある方向から偏光板６を見たときに、液晶層３のリタデーションがほぼ０になるように設定すれば、光漏れが少なくなりコントラストが改善される。
【００３９】
【発明の効果】
本発明によれば、液晶分子が水平配列した領域と垂直配列した領域とを有する液晶層の液晶表示装置を偏光板の斜め方向から見たときに、水平配列領域の液晶分子のリタデーションと垂直配列領域の液晶分子のリタデーションが相殺するように設定しているので、斜め方向から見たときの光漏れを少なくし、視角特性を向上させることができる。
【００４０】
また、誘電率異方性が負の液晶にカイラル剤を添加し、一対の基板の配向膜に配向方向が直交する配向処理を施して、液晶層に電圧を印加したときに液晶層内で液晶分子が水平状態で且つ９０度捻れて配列することにより白表示にするので、ノーマリブラックモードのハイブリッド配列型液晶表示装置でも簡単な構成で白表示が実現できる。
【図面の簡単な説明】
【図１】本発明の一実施例であるノーマリブラックモードの液晶表示装置のオフ時における液晶分子の配列状態を示す概略図である。
【図２】本発明の一実施例であるノーマリブラックモードの液晶表示装置のオン時における液晶分子の配列状態を示す概略図である。
【図３】本発明の一実施例である液晶表示装置を側面から見たときの該略図である。
【図４】本発明の一実施例である液晶表示装置を偏光板の法線方向から見たときの概略図である。
【図５】本発明の図４のＡ’−Ａ’線に沿った液晶分子の配列状態を模式的に示した図である。
【図６】液晶分子を斜めから見たときの光路と液晶分子の位置関係を説明する図である。
【図７】従来の液晶表示装置を側面から見たときの該略図である。
【図８】従来の液晶表示装置を偏光板の法線方向から見たときの概略図である。
【符号の説明】
１第１基板
１ｃ配向膜
２第２基板
２ｃ配向膜
４液晶分子
５下偏光板
６上偏光板
７ａ、７ｂ配向方向
８ａ、８ｂ透過軸[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device excellent in high-speed response and viewing angle characteristics.
[0002]
[Prior art]
Liquid crystal display devices are characterized by being thin and light and having low power consumption, and are widely used from portable terminals to personal computers and televisions. Such a liquid crystal display device is required to have a high-speed response and a wide viewing angle as its performance, and various devices have been devised to satisfy the demand. As a liquid crystal display device capable of high-speed response, for example, there is a HAN (hybrid aligned nematic) liquid crystal display device disclosed in JP-A-9-146086 or JP-A-9-197397.
[0003]
This conventional liquid crystal display device will be described with reference to FIGS. Here, a description will be given of a case of normally black, which is black when turned off. FIG. 7 is a schematic configuration diagram of the liquid crystal display device in black display (when off), and FIG. 8 is a schematic diagram showing the positional relationship between the transmission axis of the polarizing plate and the alignment state of liquid crystal molecules in black display (when off). is there.
[0004]
In this liquid crystal display device, one substrate 100b is subjected to a horizontal alignment process, and the other substrate 100a is subjected to a vertical alignment process. In an off state, the liquid crystal molecules 102 have a predetermined orientation on the horizontal alignment substrate 100b side. Are arranged horizontally with a pretilt angle of, vertically arranged on the vertically aligned substrate 100a side, and the liquid crystal layer 101 therebetween gradually changes the arrangement state from the horizontal arrangement to the vertical arrangement.
[0005]
Polarizers 103 are disposed above and below the substrate 100 with the liquid crystal layer 101 interposed therebetween. The polarizers 103 have an angle of 90 degrees between the transmission axes 107 of both polarizers 103 and correspond to the horizontally aligned substrate 100b. The transmission axis 107b of the polarizing plate 103b is set to be at 45 degrees to the horizontal alignment direction. Note that the transmission axis may be replaced with the absorption axis. In FIG. 8, the transmission axes 107b of the liquid crystal molecules 102b and the polarizing plate 103b on the substrate 100b side are shown by dotted lines, and the transmission axes 107a of the liquid crystal molecules 102a and the polarizing plate 103a on the substrate 100a side are shown by solid lines.
[0006]
An optical compensation sheet 108 is provided between the substrate 100a and the polarizing plate 103a. The optical compensatory sheet 108 has a refractive index ellipsoid such that the combined refractive index ellipsoid of the liquid crystal layer 101 and the optical compensatory sheet 108 at the time of off becomes a sphere, for example, a uniaxial or biaxial optical anisotropic body. An element is used.
[0007]
The incident light (linearly polarized light) passing through the transmission axis 107b passes through the liquid crystal molecules 102 of the liquid crystal layer 101 and the optical compensation sheet 108, and reaches the polarizing plate 103a. In the off state, the combined refractive index ellipsoid of the liquid crystal layer 101 and the optical compensation sheet 108 becomes a sphere, so that the transmitted light that reaches the polarizing plate 103a becomes linearly polarized light whose amplitude direction is the same as the transmission axis 107b. Black display (normally black mode) without passing through the transmission axis 107a.
[0008]
When a predetermined voltage is applied to the liquid crystal layer 101, the alignment state of the horizontally aligned liquid crystal molecules 102 changes to a vertical alignment, and the combined refractive index ellipsoid of the liquid crystal layer 101 and the optical compensation sheet 108 changes from a sphere to an ellipsoid. Changes to Therefore, the incident light (linearly polarized light) passing through the transmission axis 107b becomes elliptically polarized light by the birefringence effect of the liquid crystal layer 101 and the optical compensation sheet 108 when reaching the polarizing plate 103a. Display.
[0009]
[Problems to be solved by the invention]
However, the HAN-aligned liquid crystal display device can realize a good black display when viewed from the normal direction of the surface of the polarizing plate 103a, but has an optical characteristic when viewed from a direction forming a certain angle with respect to the normal direction. Leakage occurs. In particular, when the polarizing plate 103a is viewed obliquely from the direction 109 of the transmission axis 107, light leakage is small, but when the polarizing plate 103a is viewed obliquely from the direction 110 that forms an angle of 45 degrees with the transmission axis 107, light leakage is large.
[0010]
In order to prevent such light leakage, the optical compensatory sheet should be variously designed so that the combined refractive index ellipsoid of the liquid crystal layer 101 and the optical compensatory sheet 108 becomes a sphere when the polarizing plate 103a is viewed obliquely from any direction. Have been tried.
[0011]
Accordingly, the present invention provides a liquid crystal layer having a function of viewing angle compensation by canceling out the retardation of the liquid crystal molecules of the liquid crystal layer in the vertical alignment and the liquid crystal molecules in the horizontal alignment, enabling a wide viewing angle and a high-speed response. It is an object to provide a liquid crystal display device.
[0012]
[Means for Solving the Problems]
In order to solve the above problem, the invention according to claim 1 is a liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates, wherein the liquid crystal layer is vertically aligned with a region in which liquid crystal molecules are horizontally aligned in a normal direction of the substrate. The gap width of each region is set so that the retardation by the liquid crystal molecules in the horizontally arranged region and the retardation by the liquid crystal molecules in the vertically arranged region cancel each other out.
[0013]
The invention according to claim 2 is a liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates, and an alignment film of one substrate is vertically aligned, and an alignment film of the other substrate is horizontally aligned. The alignment anchoring strength of each alignment film is set so that the retardation of liquid crystal molecules aligned vertically due to the vertical alignment film and the retardation of liquid crystal molecules aligned horizontally due to the horizontal alignment film cancel each other. It is characterized by having done.
[0014]
According to a third aspect of the present invention, in a liquid crystal display device in which a pair of substrates are sandwiched between a pair of polarizing plates, an angle between a transmission axis or an absorption axis of the two polarizing plates becomes 90 degrees, and a horizontal alignment film is formed. The polarizing plate is arranged such that the transmission axis or the absorption axis of the polarizing plate corresponding to the substrate has the same direction as the horizontal alignment direction.
[0015]
According to a fourth aspect of the present invention, in the direction of 40 to 50 degrees with respect to the transmission axis or the absorption axis of the polarizing plate, and in the direction of 10 to 70 degrees with respect to the normal direction of the polarizing plate. The gap width between the horizontal alignment region and the vertical alignment region is set such that the retardation of the liquid crystal layer when the polarizing plate is viewed from a predetermined direction is substantially zero.
[0016]
The invention according to claim 5 is characterized in that a nematic liquid crystal having a negative dielectric anisotropy to which a chiral agent is added is interposed between substrates.
[0017]
According to a sixth aspect of the present invention, in the pair of substrates, the alignment film of one substrate is provided with horizontal alignment, the alignment film of the other substrate is provided with vertical alignment, and the alignment film of one substrate is provided. The alignment processing is performed in a horizontal direction orthogonal to the horizontal alignment direction performed on the substrate.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. This liquid crystal display device is in a normally black mode. FIG. 1 is a schematic configuration diagram showing an arrangement state of liquid crystal molecules in black display (when off), and FIG. 2 shows an arrangement state of liquid crystal molecules in white display (when on). FIG. 3 is a schematic configuration diagram, FIG. 3 is a schematic side view of the liquid crystal display device when the liquid crystal display device is off, and FIG.
[0019]
The first substrate 1 has a pixel electrode 1b and an alignment film 1c stacked on a glass substrate 1a, and the second substrate 2 has a transparent electrode 2b and an alignment film 2c stacked on a glass substrate 2a. After the spacers are scattered on the first substrate 1, the first substrate 1 and the second substrate 2 are opposed to each other at predetermined positions so that the respective alignment films 1c and 2c face each other, and the periphery of both

substrates

1 and 2 is removed. Secure with sealant. A nematic liquid crystal 3 having a negative dielectric anisotropy is sealed between the two

substrates

1 and 2, and the liquid crystal molecules 4 maintain an alignment described later under the influence of the alignment films 1c and 2c. Since the liquid crystal layer 3 contains a chiral agent, the liquid crystal molecules 4 are arranged when the liquid crystal layer 3 is turned on, as shown in FIG. In this embodiment, the chiral agent has a property of rotating the liquid crystal molecules 4 clockwise (clockwise).
[0020]
A lower polarizing plate 5 is arranged below the first substrate 1, and an upper polarizing plate 6 is arranged above the second substrate 2. As shown in FIG. 4, the lower polarizing plate 5 and the upper polarizing plate 6 are arranged such that their

transmission axes

8a and 8b are orthogonal to each other when viewed from the normal direction 9 of the surface thereof. The transmission axis 8a and the orientation direction 7a of the first substrate 1 are arranged in the same direction. In FIG. 4, the liquid crystal molecules 4a on the first substrate 1 side and the transmission axis 7a of the lower polarizer 5 are shown by solid lines, and the liquid crystal molecules 4a on the second substrate 2 side and the transmission axis 7b of the upper polarizer 6 are shown by dotted lines. . Since the

substrates

1 and 2 and the polarizing plates 5 and 6 are arranged so that their surfaces are parallel to each other, their normal directions 9 coincide with each other. In this embodiment, the transmission axis will be described, but an absorption axis may be used instead of the transmission axis.
[0021]
The alignment film 1c of the first substrate 1 is subjected to a horizontal alignment process, and the alignment film 2c of the second substrate 2 is subjected to a vertical alignment process. The alignment film 2c of the second substrate 2 is subjected to an alignment process in a direction 7b which is 90 degrees with respect to the horizontal alignment direction 7a of the first substrate 1c, and the liquid crystal molecules 4b on the second substrate 2 side are aligned when turned on. They are arranged in the direction 7b. In this alignment treatment, a vertical alignment film is laminated on the second substrate 2, and the vertical alignment film is irradiated with linearly polarized ultraviolet light whose amplitude direction is orthogonal to the alignment direction 7b to be formed. When the liquid crystal molecules 4 are turned on while acting on the liquid crystal molecules 4, an alignment film 2c that functions to align the liquid crystal molecules 4 in the horizontal direction of the alignment direction 7b can be formed.
[0022]
In the off state (FIG. 1), the liquid crystal molecules 4a on the first substrate 1 side are affected by the horizontal alignment of the alignment film 1c and are horizontally arranged at an inclination of the pretilt angle θ, and the liquid crystal molecules 4b on the second substrate 2 side are aligned. The films are vertically arranged under the influence of the vertical orientation of the film 2c. At this time, the gap width of the horizontal alignment region 12a and the gap width of the vertical alignment region 12b of the liquid crystal molecules 4 cause light leakage when viewed from an oblique direction having a certain angle with respect to the normal direction 9 of the upper polarizing plate 6. In such a manner, the retardation of the horizontal arrangement region 12a and the retardation of the vertical arrangement region 12b are set to cancel each other, and this is realized by adjusting the intensity of the anchoring of the alignment films 1c and 2c. In particular, if the retardation of the liquid crystal layer 3 is set to be substantially 0 when viewed from a direction forming an angle (β) of 45 degrees with respect to the transmission axes 8a and 8b, light leakage at the time of off is minimized. be able to.
[0023]
In the off state, linearly polarized light (incident light) 10 a having the same amplitude direction as the transmission axis 8 a passes through the lower polarizing plate 5 and reaches the upper polarizing plate 6 via the liquid crystal molecules 4. At this time, the transmitted light 10b that has reached the upper polarizing plate 6 is linearly polarized light having the same amplitude direction as the incident light 10a, and is thus blocked by the upper polarizing plate 6. Further, since the retardation given by the liquid crystal molecules 4a in the horizontal alignment region 12a to the transmitted light 10b and the retardation given by the liquid crystal molecules 10a in the vertical alignment region 12b to the transmitted light 10b cancel each other, for example, the transmission axis 8b and 45 degrees (β) When the display is viewed obliquely from the direction (arrow 1), black display is also performed.
[0024]
In the ON state (FIG. 2), the liquid crystal molecules having a negative dielectric anisotropy have a chiral agent added thereto, so that the liquid crystal molecules 4b in the vertical alignment state are tilted in the horizontal direction, and the liquid crystal molecules 4 in the horizontal state are shifted to the right. Rotate in the direction (clockwise). Therefore, in the liquid crystal layer 3, the liquid crystal molecules 4 are arranged while being twisted clockwise from the first substrate 1 to the second substrate 2. Furthermore, since the alignment film 2c that has been subjected to the vertical alignment processing has been subjected to the alignment processing in the horizontal direction 7b orthogonal to the alignment direction 7a of the alignment film 1c, the liquid crystal molecules 4b in the vertical alignment state 12b are not The liquid crystal molecules 4a on the first substrate 1 side and the long axis direction of the liquid crystal molecules 4b on the second substrate 2 are arranged while being twisted so as to be 90 degrees. In this embodiment, the gap width and the chiral agent of the liquid crystal layer 3 are set so that the liquid crystal molecules 4 are twisted by 90 degrees in the liquid crystal layer 3.
[0025]
The linearly polarized incident light 10 a passing through the lower polarizing plate 5 is rotated by the liquid crystal molecules 4 and reaches the upper polarizing plate 6. The transmitted light 10c that has reached the upper polarizing plate 6 is linearly polarized in the same direction as the transmission axis 8b in the amplitude direction.
[0026]
As described above, in the normally black mode HAN-aligned liquid crystal display device, the liquid crystal molecules 4 are twisted in a horizontal alignment state when turned on, so that white display can be achieved with a simple configuration without providing an optical compensation sheet or the like. realizable.
[0027]
Next, an example of the gap width of the horizontal arrangement region and the gap width of the vertical arrangement region will be described. FIG. 5 is a schematic side view taken along the line A'-A 'of FIG. 4, and the liquid crystal layer 3 is divided into two regions of a vertical arrangement region 12b and a horizontal arrangement region 12a for simplicity of description and calculation. All the liquid crystal molecules 4b in the vertical alignment region 12b are vertically aligned parallel to the normal direction 9 of the substrate, and all the liquid crystal molecules 4a in the horizontal alignment region 12a are horizontally aligned in a direction orthogonal to the normal direction 9 of the substrate. I do. In this example, the retardation when viewing the liquid crystal layer 3 from the direction forming 45 ° (β) with the transmission axis 8b and the direction of 70 ° (α) with respect to the normal direction 9 of the substrate becomes almost zero. Set as follows.
[0028]
The refractive index of the liquid crystal molecules 4 long axis _n x = 1.5575, a minor axis direction _n y = 1.4754, the gap width of the liquid crystal layer 3 is vertically aligned region 12b is _{d v,} the horizontal arrangement region 12a is _{d h} And
[0029]
When α = 70 °, the light traveling direction α ′ in the liquid crystal layer 3 is about 38 ° (FIG. 5). Further, the angle gamma ₁ of the long axis of the traveling direction and the liquid crystal molecules 4a of the light in the liquid crystal layer 3 is about 64 °, the vibration direction of the light refractive index is maximum (hereinafter, referred to as the vibration direction 1) and liquid crystal angle gamma ₂ between the long axes of the molecules become _{_{γ 2 = 90 ° -γ 1 =}} 26 °.
[0030]
FIG. 6 shows the relationship among α, γ ₁ , γ _{2 and the} like. In FIG. 6, the major axis of the liquid crystal molecules 4a is on the X axis, the positive area of the Z axis is in the air, and the negative area is the liquid crystal layer. An A'-A 'line on the XY plane indicates a line when the optical path (arrow 1) is projected on the XY plane. Here, when the origin is viewed from the direction (optical path) between the Z axis and α and the Y axis and β in the positive region of the Z axis, the Z axis and α ′ and the Y axis are 45 ° in the negative region of the Z axis (liquid crystal layer). Obtain an optical path in the direction of Angle is gamma ₁ next to the optical path and the X-axis (the long axis of the liquid crystal molecules) in the negative region of the Z-axis of this time, the line and the X axis is an angle that intersects the X-axis perpendicular to the optical path gamma ₂ and Become. The vibration direction 1 is such that the vibration component is orthogonal to the optical path and ordinary light with respect to light (ordinary light) in which the oscillation component is orthogonal to the optical path and the direction of the oscillation component and the X axis (the major axis direction of the liquid crystal molecules) form 90 °. In addition, the direction intersects the X axis.
[0031]
Next, the retardation R (h, α) in the horizontal array region 12a when α = 70 ° and β = 45 ° is calculated. At this time, the refractive index _nxh (α) in the vibration direction 1 in the horizontal alignment region 12a is represented by the following equation.
[0032]
_{_{_{n xh (α) = n x}}} · n y / (n x 2 · sin 2 γ 2 + n y 2 · cos 2 γ 2) 0.5
The ordinary refractive index _{n yh} (alpha) can be expressed by _{_{n yh (α) = n y}} , optical path in a horizontal array region d (h, α) is _{d (h, α) = d} h / cosα '. Therefore, the retardation R (h, α) in the horizontal array region 12a can be expressed by the following equation.
[0033]

Further, the retardation R (v, α) in the vertical array region 12b when α = 70 ° and β = 45 ° is calculated. The extraordinary light refractive index n _xv (α) in the vertical alignment region 12b at this time is represented by the following equation.
[0034]
_{_{_{n xv (α) = n x}}} · n y / (n x 2 · cos 2 α '+ n y 2 · sin 2 α') 0.5
The ordinary refractive index _{n yv} (alpha) is _{_{n yv (α) = n y}} , optical path d (v, α) in the vertical arrangement region 12b can be expressed by _{d (v, α) = d} v / cosα '. Therefore, the retardation R (v, α) in the vertical array region 12b can be expressed by the following equation.

Here, when viewed from the directions of α = 70 ° and β = 45 °, the angle γ ₃ formed by the long axis direction of the projected vertical alignment liquid crystal molecules 4b and the long axis direction of the projected horizontal alignment liquid crystal molecules 4a. Is about 52 °, and the total retardation R (α, β) of the liquid crystal layer is approximately expressed by the following equation.
[0035]

And R (α, β) when the = _0, holds the relationship of d h = 2.714d _v. Here if the gap width of the entire liquid crystal layer is _{_5~6μm,} d v = _1580nm, by setting the d h = 4289nm α = 70 ° , the retardation when viewed from the direction of β = 45 ° R (α, β) becomes substantially 0, and a liquid crystal display device having small viewing angle dependence in this direction can be realized. It should be noted that, at this time Δn _· d v = 130, becomes Δn _· d h = 352.
[0036]
Thus determined gap width d _v, to set the strength of the orientation anchoring of the alignment film 1c, 2c so that the d _h. Here determined gap width d _v, d _h is a value when the liquid crystal molecules 4 of the liquid crystal layer 3 are arranged as shown in FIG. However, the horizontally aligned liquid crystal molecules 4a are inclined at the pretilt angle θ, and the alignment state of the liquid crystal molecules 4 from the first substrate 1 to the second substrate 2 is gradually changed from horizontal alignment to vertical alignment. Thus obtained gap width d _v, by adjusting the respective gap width to an appropriate value by experiment or the like after setting the d _h, serving as the liquid crystal display device in which light leakage is improved less contrast at the time of black display.
[0037]
The alignment anchoring gap width d _v of obtaining the _strength, if possible strong satisfying a condition of d _h, increases the range occupied by the horizontal arrangement region 12a and a vertical array area 12b, the vertical array from the horizontal arrangement The area of the liquid crystal molecules 4 where the alignment state changes can be reduced. This way alignment state of the liquid crystal molecules 4 becomes close to the arrangement state shown in FIG. 5, the gap width d _v, the calculated value of d _h can be effectively utilized. Further, if an optical compensation sheet is added to the liquid crystal display device in which each gap width is set in this way, the viewing angle dependency can be further eliminated, and the viewing angle characteristics can be improved.
[0038]
In this embodiment, the case where α = 70 ° and β = 45 ° has been described. However, the present invention is not limited to this direction. When the upper polarizing plate 6 is viewed obliquely from another direction, the liquid crystal layer 3 May be set to be substantially zero. However, since light leakage is large when viewed from the direction of β = 45 °, when the polarizing plate 6 is viewed from a certain direction in a range where β is in the range of 40 to 50 degrees and α is in the range of 10 to 70 degrees. If the retardation of the liquid crystal layer 3 is set to substantially zero, light leakage is reduced and the contrast is improved.
[0039]
【The invention's effect】
According to the present invention, when a liquid crystal display device having a liquid crystal layer having a region in which liquid crystal molecules are horizontally aligned and a region in which liquid crystal molecules are vertically arranged is viewed from an oblique direction of a polarizing plate, retardation and vertical alignment of liquid crystal molecules in a horizontal alignment region are performed. Since the retardation of the liquid crystal molecules in the region is set to cancel each other, light leakage when viewed from an oblique direction can be reduced, and the viewing angle characteristics can be improved.
[0040]
In addition, a chiral agent is added to a liquid crystal having a negative dielectric anisotropy, and an alignment process is performed so that the alignment directions of the pair of substrates are orthogonal to each other. Since white display is performed by arranging the molecules in a horizontal state and twisting 90 degrees, white display can be realized with a simple configuration even in a normally black mode hybrid alignment type liquid crystal display device.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an alignment state of liquid crystal molecules when a normally black mode liquid crystal display device according to an embodiment of the present invention is off.
FIG. 2 is a schematic diagram showing an arrangement state of liquid crystal molecules when a normally black mode liquid crystal display device according to an embodiment of the present invention is turned on.
FIG. 3 is a schematic view of a liquid crystal display device according to an embodiment of the present invention when viewed from a side.
FIG. 4 is a schematic view of a liquid crystal display device according to one embodiment of the present invention when viewed from a normal direction of a polarizing plate.
FIG. 5 is a diagram schematically showing an alignment state of liquid crystal molecules along the line A′-A ′ in FIG. 4 of the present invention.
FIG. 6 is a diagram illustrating a positional relationship between an optical path and liquid crystal molecules when the liquid crystal molecules are viewed obliquely.
FIG. 7 is a schematic view when a conventional liquid crystal display device is viewed from a side.
FIG. 8 is a schematic diagram when a conventional liquid crystal display device is viewed from a normal direction of a polarizing plate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st substrate 1c Alignment film 2 2nd substrate 2c Alignment film 4 Liquid crystal molecule 5 Lower polarizing plate 6

Upper polarizing plate

7a,

7b Alignment direction

8a, 8b Transmission axis

Claims

In a liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates, the liquid crystal layer has a region in which liquid crystal molecules are horizontally arranged and a region in which liquid crystal molecules are vertically arranged in a normal direction of the substrate, and retardation of the horizontally arranged region by the liquid crystal molecules. A liquid crystal display device characterized in that the gap width of each region is set such that the retardations of the liquid crystal molecules in the regions vertically aligned with each other cancel each other.

In a liquid crystal display device in which a liquid crystal layer is interposed between a pair of substrates, an alignment film of one substrate is vertically aligned, and an alignment film of the other substrate is horizontally aligned, the liquid crystal layer is affected by the vertical alignment film. Liquid crystal molecules wherein the alignment anchoring strength of each alignment film is set such that the retardation of liquid crystal molecules aligned vertically and the retardation of liquid crystal molecules aligned horizontally affected by the horizontal alignment film cancel each other. Display device.

In a liquid crystal display device in which the substrate is sandwiched between a pair of polarizing plates, the angle between the transmission axis or the absorption axis of both polarizing plates becomes 90 degrees, and the transmission axis of the polarizing plate corresponding to the substrate having the horizontal alignment film. 3. The liquid crystal display device according to claim 1, wherein the polarizing plate is arranged so that the absorption axis is in the same direction as the horizontal alignment direction.

A predetermined angle within a range of 40 to 50 degrees with respect to the transmission axis or the absorption axis of the polarizing plate, and a direction included in a direction of 10 to 70 degrees with respect to the normal direction of the polarizing plate. The gap width between the horizontal arrangement region and the vertical arrangement region is set so that the retardation of the liquid crystal layer when the polarizing plate is viewed from a direction is substantially zero. 3. The liquid crystal display device according to 3.

5. The liquid crystal display device according to claim 1, wherein a nematic liquid crystal having a negative dielectric anisotropy added with a chiral agent is interposed between the substrates.

Among the pair of substrates, the horizontal alignment direction is applied to the alignment film of one substrate, the vertical alignment is applied to the alignment film of the other substrate, and the horizontal alignment direction is applied to the alignment film of the one substrate. 6. The liquid crystal display device according to claim 1, wherein an alignment process is performed in a horizontal direction orthogonal to the horizontal direction.