JP2004093713A

JP2004093713A - Liquid crystal display

Info

Publication number: JP2004093713A
Application number: JP2002252310A
Authority: JP
Inventors: Tomoko Tano; 田野　朋子
Original assignee: Casio Computer Co Ltd
Current assignee: Casio Computer Co Ltd
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2004-03-25

Abstract

【課題】電界印加画素に隣接した無電界画素に対応する明表示部に、前記電界印加画素の影が生じるのを防ぎ、二重像の無い良好な品質の画像を表示することができる反射型液晶表示装置を提供する。
【解決手段】液晶分子が９０°のツイスト角でツイスト配向した液晶セル１の前側に前側偏光板１０を配置し、液晶セル１の後側に後側偏光板１２をその吸収軸１２ａを前側偏光板１０の吸収軸１０ａと直交させて配置し、後側偏光板１２の後側に反射手段１４を配置するとともに、液晶セル１と前側偏光板１０との間に、フィルム面に平行な面上に最も屈折率が大きいｘ軸とそれと直交するｙ軸を有し、これらの軸と直交する方向に最も屈折率が小さいｚ軸を有する二軸性位相差板１１を、そのｘ軸１１ｘを前側偏光板１０の吸収軸１０ａと平行にして配置し、液晶セル１のΔｎｄの値を３８０〜４２０ｎｍ、二軸性位相差板１１の面内位相差を２００〜３５０ｎｍ、Ｎｚ係数を１．５以上とした。
【選択図】　　図１A reflection type display device capable of preventing a shadow of an electric field application pixel from being generated on a bright display portion corresponding to a non-electric field pixel adjacent to an electric field application pixel and displaying a good quality image without a double image. Provided is a liquid crystal display device.
A front polarizer (10) is disposed on the front side of a liquid crystal cell (1) in which liquid crystal molecules are twisted at a twist angle of 90 °, and a rear polarizer (12) is disposed on the rear side of the liquid crystal cell (1). The liquid crystal cell 1 is arranged perpendicular to the absorption axis 10a of the plate 10, the reflecting means 14 is arranged behind the rear polarizing plate 12, and the liquid crystal cell 1 and the front polarizing plate 10 A biaxial retardation plate 11 having an x-axis having the largest refractive index and a y-axis perpendicular thereto, and having a z-axis having the smallest refractive index in a direction perpendicular to these axes. The liquid crystal cell 1 is arranged in parallel with the absorption axis 10a of the polarizing plate 10, the value of Δnd of the liquid crystal cell 1 is 380 to 420 nm, the in-plane retardation of the biaxial retardation plate 11 is 200 to 350 nm, and the Nz coefficient is 1.5 or more. And
[Selection diagram] Fig. 1

Description

【０００１】
【発明の属する技術分野】
この発明は、外光を利用する反射表示を行なう液晶表示装置に関する。
【０００２】
【従来の技術】
液晶表示装置としては、ＴＮ（ツイステッドネマティック）型のものが広く利用されている。
【０００３】
このＴＮ型液晶表示装置は、表示の観察側である前側の基板とこの前側基板に対向する後側基板の互いに対向する内面にそれぞれ、互いに対向する領域により複数の画素を形成するための電極が設けられ、これらの基板間に液晶分子が実質的に９０°のツイスト角でツイスト配向した液晶層が設けられてなる液晶セルと、前記液晶セルの前側に配置された前側偏光板と、前記液晶セルの後側に配置された後側偏光板とからなっている。
【０００４】
また、液晶表示装置には、前記後側偏光板の後側に反射膜を配置した反射型のものがあり、ＴＮ型の反射型液晶表示装置は、前記前側偏光板を、その吸収軸と透過軸のいずれか一方を前記液晶セルの前側基板の近傍における液晶分子配向方向と実質的に平行にして配置し、前記後側偏光板を、その吸収軸を前記前側偏光板の吸収軸に対して実質的に直交させて配置した構成とされている。
【０００５】
この反射型液晶表示装置は、その使用環境の光である外光を利用する反射表示を行なうものであり、表示の観察側である前側から入射し、前側偏光板により直線偏光とされて液晶セルに入射した光のうち、前記液晶セルの無電界画素（液晶層の液晶分子が初期のツイスト配向状態にある画素）を透過し、さらに後側偏光板を透過してその後側に出射した光を反射膜により反射し、その反射光を、前記後側偏光板と液晶セルの無電界画素と前側偏光板とを透過させて前側に出射させることにより明表示（白黒表示の場合は白表示）を得、前記液晶セルの電界印加画素（液晶層の液晶分子が基板面に対して実質的に垂直に立ち上がり配向した画素）を透過した光を前記後側偏光板により吸収して黒表示を得る。
【０００６】
【発明が解決しようとする課題】
前記反射型液晶表示装置は、外光が様々な入射方位（画面の法線回りの方向）及び入射角で入射するため、前記液晶セルの無電界画素に対応する明表示は、画面（前側偏光板の前面）の法線付近の方向から前記無電界画素を透過して入射し、反射膜により反射されて同じ無電界画素を透過して前側に出射する光と、前記画面の法線に対して斜め方向から他の画素を透過して入射し、前記反射膜により反射されて前記無電界画素を透過して前側に出射する光とにより表示される。
【０００７】
一方、前記液晶セルの電界印加画素に対応する暗表示は、前側偏光板により直線偏光とされて液晶セルに入射した光のうち、画面の法線付近の方向から入射して前記液晶セルの電界印加画素を透過した光が後側偏光板により吸収されることにより表示される。
【０００８】
しかし、従来の反射型液晶表示装置では、前記画面の法線に対して斜め方向から入射する光が、前記液晶セルの電界印加画素を透過した後、後側偏光板により高い吸収率で吸収されるため、前記液晶セルの電界印加画素に隣接する無電界画素に対応する明表示部に、前記斜め方向から入射する光の反射光が得られない領域ができ、その領域が暗くなって前記電界印加画素の影ができる。
【０００９】
したがって、前記反射型液晶表示装置は、前記電界印加画素による本来の黒表示と、その黒表示の影とが二重像となって観察され、表示画像がボケたり滲んだりして見える。
【００１０】
この発明は、二重像の無い良好な品質の画像を表示することができる反射型の液晶表示装置を提供することを目的としたものである。
【００１１】
【課題を解決するための手段】
この発明の液晶表示装置は、
表示の観察側である前側の基板とこの前側基板に対向する後側基板の互いに対向する内面にそれぞれ、互いに対向する領域により複数の画素を形成するための電極が設けられ、これらの基板間に液晶分子が実質的に９０°のツイスト角でツイスト配向した液晶層が設けられてなる液晶セルと、前記液晶セルの前側に配置された前側偏光板と、前記液晶セルと前記前側偏光板との間に配置された位相差素子と、前記液晶セルの後側に配置された後側偏光板と、前記後側偏光板の後側に配置され、前側から入射した光を反射する反射手段とを備え、
前記前側偏光板が、その吸収軸と透過軸のいずれか一方を前記液晶セルの前側基板の近傍における液晶分子配向方向と実質的に平行にして配置され、前記後側偏光板が、その吸収軸を前記前側偏光板の吸収軸に対して実質的に直交させて配置されるとともに、
前記液晶セルの液晶の屈折率異方性Δｎと液晶層厚の積Δｎｄの値が３８０〜４２０ｎｍに設定され、
前記位相差素子は、光学的に二軸性を有するフィルムからなり、そのフィルム面に平行な面上に、最も屈折率が大きいｘ軸とそれと直交するｙ軸を、これらの軸とそれぞれ直交する方向に、最も屈折率が小さいｚ軸を有し、前記ｘ軸方向の屈折率をｎ_ｘ、前記ｙ軸方向の屈折率をｎ_ｙ、前記ｚ軸方向の屈折率をｎ_ｚとしたとき、前記ｘ軸方向の屈折率ｎ_ｘと前記ｙ軸方向の屈折率ｎ_ｙとの差が２００〜３５０ｎｍ、Ｎｚ＝（ｎ_ｘ−ｎ_ｚ）／（ｎ_ｘ−ｎ_ｙ）の式で表わされるＮｚ係数が１．５以上である二軸性位相差板からなっており、この二軸性位相差板が、前記ｘ軸を前記前側偏光板の吸収軸と実質的に平行にして配置されていることを特徴とする。
【００１２】
この液晶表示装置は、その使用環境の光である外光を利用する反射表示を行なうものであり、前記液晶セルの無電界画素に対応する明表示を、画面（前側偏光板の前面）の法線付近の方向から前記無電界画素を透過して入射し、反射手段により反射されて同じ無電界画素を透過して前側に出射する光と、前記画面の法線に対して斜め方向から隣接する無電界画素及び電界印加画素に入射し、前記反射手段により反射されて前記無電界画素を透過して前側に出射する光とにより表示し、前記液晶セルの電界印加画素に対応する黒表示は、前記画面の法線付近の方向から入射し、前記電界印加画素を透過した光が後側偏光板によって吸収され、且つ前記反射手段により反射された光の正面反射光（画面の法線付近の方向）が前記電界印加画素を透過した後、前側偏光板によって吸収されることによって表示する。
【００１３】
この液晶表示装置では、前記液晶セルと前側偏光板との間に前記二軸性位相差板を配置しているため、表示の観察側である前側から前側偏光板により直線偏光とされて入射した光のうち、前記画面の法線付近の方向、つまり前記二軸性位相差板の屈折率が最も小さいｚ軸に沿った方向から入射した正面入射光は、前記二軸性位相差板を偏光状態をほとんど変えずに透過して前記液晶セルに入射し、前記画面の法線に対して斜め方向、つまり前記二軸性位相差板のｚ軸に対して斜め方向から入射した斜め入射光は、前記二軸性位相差板により偏光状態を変えられて前記液晶セルに入射する。
【００１４】
そのため、この液晶表示装置によれば、前記液晶セルの無電界画素を透過した斜め入射光も、前記液晶セルの電界印加画素を透過した斜め入射光も、後側偏光板の透過軸に平行な直線偏光成分を含んだ偏光状態の光として前記後側偏光板に入射させ、この後側偏光板を透過した直線偏光を反射手段により反射させることができる。
【００１５】
しかも、この液晶表示装置では、前記液晶セルのΔｎｄの値を３８０〜４２０ｎｍに設定し、前記二軸性位相差板のｘ軸方向の屈折率ｎ_ｘとｙ軸方向の屈折率ｎ_ｙとの差を２００〜３５０ｎｍ、Ｎｚ＝（ｎ_ｘ−ｎ_ｚ）／（ｎ_ｘ−ｎ_ｙ）の式で表わされるＮｚ係数を１．５以上とし、この二軸性位相差板を、前記ｘ軸を前記前側偏光板の吸収軸と実質的に平行にして配置しているため、前記無電界画素を透過した斜め入射光も、前記電界印加画素を透過した斜め入射光も、前記後側偏光板の透過軸に平行な直線偏光成分をより多い比率で含んだ偏光状態の光として前記後側偏光板に入射させ、より多くの光を前記後側偏光板を透過させて前記反射手段により反射させることができる。
【００１６】
そのため、前記液晶セルの無電界画素に対応する明表示は、画面の法線付近の方向から前記無電界画素を透過して入射した光の正面反射光（同じ無電界画素を往復して透過して前側に出射する光）に、斜め方向から他の無電界画素を透過して入射した光の正面反射光が加えられた明るさである。また、電界印加画素に隣接した無電界画素に対応する明表示は、前記画面の法線付近の方向から前記無電界画素を透過して入射した光の正面反射光に、斜め方向から隣接した他の電界印加画素を透過して入射した光の正面反射光が加えられた明るさであり、この隣接した電界印加画素を透過して入射し、この電界印加画素に隣接する無電界画素を透過する正面反射光は充分な明るさをもった光である。
【００１７】
したがって、この液晶表示装置によれば、前記液晶セルの電界印加画素に斜めに入射した光が吸収されることなく前記液晶セルの無電界画素から正面方向に出射するから、前記無電界画素に対応する明表示部に前記電界印加画素の影が生じることがなく、二重像の無い良好な品質の画像を表示することができる。
【００１８】
このように、この発明の液晶表示装置は、液晶層の液晶分子が実質的に９０°のツイスト角でツイスト配向した液晶セルの前側に、前側偏光板をその吸収軸と透過軸のいずれか一方を前記液晶セルの前側基板の近傍における液晶分子配向方向と実質的に平行にして配置し、前記液晶セルの後側に、後側偏光板をその吸収軸を前記前側偏光板の吸収軸に対して実質的に直交させて配置し、前記後側偏光板の後側に反射手段を配置するとともに、前記液晶セルと前記前側偏光板との間に、光学的に二軸性を有するフィルムからなり、そのフィルム面に平行な面上に最も屈折率が大きいｘ軸とそれと直交するｙ軸を有し、これらの軸とそれぞれ直交する方向に最も屈折率が小さいｚ軸を有する二軸性位相差板を、前記ｘ軸を前記前側偏光板の吸収軸と実質的に平行にして配置し、さらに前記液晶セルのΔｎｄの値を３８０〜４２０ｎｍ、前記二軸性位相差板の前記ｘ軸方向の屈折率ｎ_ｘと前記ｙ軸方向の屈折率ｎ_ｙとの差を２００〜３５０ｎｍ、Ｎｚ＝（ｎ_ｘ−ｎ_ｚ）／（ｎ_ｘ−ｎ_ｙ）の式で表わされるＮｚ係数を１．５以上とすることにより、前記液晶セルの無電界画素に対応する明表示部に、前記液晶セルの電界印加画素を透過した斜め入射光の正面反射光を増大させ、前記電界印加画素の影が生じるのを防ぎ、二重像の無い良好な品質の画像を表示することができるようにしたものである。
【００１９】
この発明の液晶表示装置において、前記二軸性位相差板は、例えばポリカーボネートの２軸延伸フィルムからなっている。
【００２０】
この液晶表示装置においては、前記液晶セルと反射手段との間または前記反射手段に光拡散手段を設けるのが好ましい。
【００２１】
また、前記反射手段は、前側に照明光を出射する面光源を備えているのが望ましい。
【００２２】
【発明の実施の形態】
以下、この発明の一実施例を図１〜図５を参照して説明する。図１はこの実施例の液晶表示装置の分解斜視図、図２は前記液晶表示装置の一部分のハッチングを省略した断面図である。
【００２３】
この実施例の液晶表示装置は、図１及び図２に示したように、液晶セル１と、前記液晶セル１の前側に配置された前側偏光板１０と、前記液晶セル１と前側偏光板１０との間に配置された位相差素子１１と、前記液晶セル１の後側に配置された後側偏光板１２と、前記液晶セル１と後側偏光板１２との間に設けられた光拡散層（以下、拡散層と言う）１３と、前記後側偏光板１２の後側に配置され、前側から入射した光を反射する反射手段１４とを備えている。
【００２４】
前記表示セル１は、表示の観察側である前側の透明基板２と、この前側基板２に対向する後側の透明基板３とが枠状のシール材４を介して接合され、これらの基板２，３の互いに対向する内面にそれぞれ、互いに対向する領域により複数の画素Ａを形成するための透明電極５，６が設けられるとともに、前記前側基板２と後側基板３との間の前記シール材４により囲まれた領域に液晶層９が設けられたものである。
【００２５】
なお、この液晶セル１は、前側基板２の内面に一枚膜状の対向電極５が設けられ、後側基板３の内面の行方向及び列方向にマトリックス状に配列する複数の画素電極６が設けられたアクティブマトリックス型液晶セルであり、図では省略しているが、前記後側基板３の内面に、前記複数の画素電極６にそれぞれ接続された複数のＴＦＴ（薄膜トランジスタ）と、各行のＴＦＴにゲート信号を供給する複数のゲート配線と、各列のＴＦＴにデータ信号を供給する複数のデータ配線とが設けられている。
【００２６】
前記液晶セル１の液晶層９の液晶分子９ａは、前後の基板２，３の内面に前記電極５，６を覆って設けられた配向膜７，８によりそれぞれの基板２，３の近傍における配向方向を規定され、前記基板２，３間において実質的に９０°のツイスト角でツイスト配向している。
【００２７】
すなわち、図１のように、前記液晶セル１の前側基板２の近傍における液晶分子配向方向２ａは、例えば画面（前側偏光板の前面）の横軸Ｏに対し、前側から見て左回りに４５°の方向、後側基板３の近傍における液晶分子配向方向３ａは、前記横軸Ｏに対し、前側から見て右回りに４５°の方向にあり、前記液晶層９の液晶分子９ａは、そのツイスト方向を破線矢印で示したように、後側基板３から前側基板２に向かい、前側から見て右回りに実質的に９０°のツイスト角でツイスト配向している。
【００２８】
なお、図２は、前記液晶セル１の一部の画素Ａの電極５，６間に、液晶分子９ａを基板２，３面に対して実質的に垂直に立ち上がり配向させる電界を印加した状態を示している。
【００２９】
また、前記液晶セル１の液晶の屈折率異方性Δｎと液晶層厚の積Δｎｄの値（画面の法線方向からの入射光に対する値）は、可視光帯域の中間波長である５５０ｎｍの波長光に対して３８０〜４２０ｎｍの範囲に設定されている。
【００３０】
そして、前側偏光板１０は、その吸収軸１０ａと透過軸（図示せず）のいずれか一方、例えば吸収軸１０ａを、前記液晶セル１の前側基板２の近傍における液晶分子配向方向２ａと実質的に平行な方向（画面の横軸Ｏに対し、前側から見て左回りに４５°の方向）に向けて配置され、前記後側偏光板１２は、その吸収軸１２ａを、前記前側偏光板１０の吸収軸１０ａに対して実質的に直交する方向（画面の横軸Ｏに対し、前側から見て左回りに１３５°の方向）に向けて配置されている。
【００３１】
また、前記液晶セル１と前側偏光板１０との間に配置された位相差素子１１は、光学的に二軸性を有するフィルムからなり、そのフィルム面に平行な面上に、最も屈折率が大きいｘ軸とそれと直交するｙ軸を、これらの軸とそれぞれ直交する方向に、最も屈折率が小さいｚ軸を有する二軸性位相差板であり、例えば、ポリカーボネートの２軸延伸フィルムからなっている。
【００３２】
この二軸性位相差板１１は、前記ｘ軸方向の屈折率をｎ_ｘ、前記ｙ軸方向の屈折率をｎ_ｙ、前記ｚ軸方向の屈折率をｎ_ｚとしたとき、前記ｘ軸方向の屈折率ｎ_ｘと前記ｙ軸方向の屈折率ｎ_ｙとの差（以下、面内位相差と言う）が、５５０ｎｍの波長光に対して２００〜３５０ｎｍの範囲で、Ｎｚ＝（ｎ_ｘ−ｎ_ｚ）／（ｎ_ｘ−ｎ_ｙ）の式で表わされるＮｚ係数が、１．５以上である特性を有している。
【００３３】
そして、この二軸性位相差板１１は、図１のように、その最も屈折率が大きいｘ軸１１ｘを、前記前側偏光板１０の吸収軸１０ａと実質的に平行な方向（画面の横軸Ｏに対し、前側から見て左回りに４５°の方向）に向けて配置されている。
【００３４】
一方、前記反射手段１４は、前記後側偏光板１２の後面に対向させて配置された鏡面反射膜１５と、この反射膜１５の前に設けられ、前側に照明光を出射する面光源１６とからなっている。
【００３５】
前記面光源１６は、アクリル系樹脂板等の透明板からなり、一端面が光を入射させる入射端面とされた導光板１７と、この導光板１７の前記入射端面に対向させて設けられた発光素子１８とからなっており、前記反射膜は、前記導光板１７の後面に蒸着またはメッキにより形成されている。
【００３６】
なお、この実施例で用いた面光源１６は、ＬＥＤ（発光ダイオード）からなる複数の発光素子１８を前記導光板１７の入射端面に対向させて配置したものであるが、前記導光板１７の入射端面に対向させて配置する発光素子は、直管状の冷陰極管等でもよい。
【００３７】
前記反射手段１４は、前記面光源１６の導光板１７の前側から入射した光が前記導光板１７内を透過して前記反射膜１５により反射され、その反射光を前記導光板１６の前側に出射するとともに、前記面光源１６の発光素子１８を点灯させることにより、この発光素子１８が出射する照明光を、前記導光板１６により導いてその前面から前側に出射するものであり、前記発光素子１８からの照明光は、前記導光板１７にその入射端面から入射し、この導光板１７の後面に設けられた反射膜１５による反射と、前記導光板１７の前面と外気（空気）との界面での全反射を繰り返しながら導光板１７内に拡散されて導かれ、この導光板１７の前面の全域から出射する。
【００３８】
この実施例の液晶表示装置は、充分な照度の使用環境下では、その使用環境の光である外光を利用する反射表示を行ない、充分な明るさの外光が得られないときに、前記反射手段１４の面光源１６から照明光を出射させて透過表示を行なうものであり、その表示は、正面方向（画面の法線付近の方向）から観察される。
【００３９】
まず、外光を利用する反射表示について説明すると、外光は、図２に矢線で示したように、表示の観察側である前側から、様々な入射方位（画面の法線回りの方向）及び入射角で入射し、前側偏光板１０によりその吸収軸１０ａに平行な偏光成分を吸収され、この前側偏光板１０の透過軸と平行な直線偏光となって前記二軸性位相差板１１に入射する。
【００４０】
前記二軸性位相差板１１は、上述したように、光学的に二軸性を有するフィルムからなっており、そのフィルム面に平行な面上に最も屈折率が大きいｘ軸とそれと直交するｙ軸を有し、これらの軸とそれぞれ直交する方向に最も屈折率が小さいｚ軸を有しているため、前記屈折率が最も小さいｚ軸に沿った方向から入射した光に対してはほとんど位相差を与えず、前記ｚ軸に対して斜め方向から入射した光に対して位相差を与える。
【００４１】
そのため、前記前側偏光板１０により直線偏光とされて前記二軸性位相差板１１に入射した光のうち、前記画面の法線に沿った方向、つまり前記二軸性位相差板１１のｚ軸に沿った方向から入射した正面入射光は、前記二軸性位相差板１１を偏光状態をほとんど変えること無く透過して液晶セル１に入射する。
【００４２】
前記液晶セル１に入射した正面入射光のうち、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}、つまり液晶層９の液晶分子９ａが初期のツイスト配向状態にある画素に入射した光は、この無電界画素Ａ_{（ＯＦＦ）}を液晶層９の複屈折作用により実質的に９０°旋光されて透過して、後側偏光板１２の透過軸（図示せず）に平行な直線偏光となり、その光が、拡散層１３により拡散されて前記後側偏光板１２に入射し、この後側偏光板１２を透過して反射手段１４により反射される。
【００４３】
前記反射手段１４により反射された反射光は、前記後側偏光板１２を再び透過し、さらに前記拡散層１３により拡散されて前記液晶セル１にその後側から入射する。
【００４４】
そして、前記液晶セル１にその後側から入射した反射光のうち、表示の観察方向である正面方向に向かう正面反射光は、上述した前側からの入射経路で透過した前記無電界画素Ａ_{（ＯＦＦ）}に入射し、この無電界画素Ａ_{（ＯＦＦ）}を透過して実質的に９０°旋光され、前側偏光板１０の透過軸（図示せず）に平行な直線偏光となり、その光が、前記二軸性位相差板１１を偏光状態をほとんど変えること無く透過し、さらに前記前側偏光板１０を透過して前側に出射する。
【００４５】
一方、前記液晶セル１に入射した正面入射光のうち、前記液晶セル１の電界印加画素Ａ_（ＯＮ）、つまり液晶層９の液晶分子９ａが基板２，３面に対して実質的に垂直に立ち上がり配向した画素に入射した光は、この電界印加画素Ａ_（ＯＮ）を液晶層９の複屈折作用をほとんど受けること無く透過し、前記拡散層１３を透過して前記後側偏光板１２により吸収される。図２において、●は光の吸収を示している。
【００４６】
また、前記前側偏光板１０により直線偏光とされて前記二軸性位相差板１１に入射した光のうち、前記画面の法線に対して斜め方向、つまり前記二軸性位相差板１１のｚ軸に対して斜め方向から入射した斜め入射光は、前記二軸性位相差板１１により常光と異常光との間に位相差を与えられ、偏光状態を変えて液晶セル１に入射する。
【００４７】
この二軸性位相差板１１を透過した斜め入射光の偏光状態は、前記二軸性位相差板１１への入射角により異なり、その入射角（二軸性位相差板１１のｚ軸に対する角度）が大きくなるほど、前記直線偏光からの偏光状態の変化が大きくなる。
【００４８】
前記液晶セル１に入射した斜め入射光は、前記液晶セル１の無電界画素（液晶分子９ａが初期のツイスト配向状態にある画素）Ａ_{（ＯＦＦ）}または電界印加画素（液晶分子９ａが基板２，３面に対して実質的に垂直に立ち上がり配向した画素）Ａ_（ＯＮ）を、液晶層９の複屈折作用によりさらに偏光状態を変えて透過する。
【００４９】
すなわち、前記斜め入射光は前記液晶セル１の液晶層９を斜めに透過するため、前記無電界画素Ａ_{（ＯＦＦ）}に入射した斜め入射光は、この無電界画素Ａ_{（ＯＦＦ）}の液晶層９による上述した正面入射光とは異なる複屈折作用を受けて偏光状態を変え、前記電界印加画素Ａ_（ＯＮ）に入射した斜め入射光は、この電界印加画素Ａ_（ＯＮ）の液晶層９による複屈折作用を受けて偏光状態を変える。
【００５０】
前記二軸性位相差板１１を透過して偏光状態を変え、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}または電界印加画素Ａ_（ＯＮ）を透過してさらに偏光状態を変えた斜め入射光は、前記拡散層１３により拡散されて後側偏光板１２に入射し、その光のうち、前記後側偏光板１２の吸収軸１２ａに平行な偏光成分がこの後側偏光板１２により吸収され、前記後側偏光板１２を透過した直線偏光（後側偏光板１２の透過軸に平行な偏光成分の光）が、この後側偏光板１２を透過して反射手段１４により反射される。
【００５１】
前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}を透過した斜め入射光と、前記液晶セル１の電界印加画素Ａ_（ＯＮ）を透過した斜め入射光とは、偏光状態が異なる光であり、したがって、これらの斜め入射光は、異なる透過率で前記後側偏光板１２を透過して反射手段１４により反射される。
【００５２】
前記反射手段１４により反射された反射光は、前記後側偏光板１２を再び透過し、さらに前記拡散層１３により拡散されて前記液晶セル１にその後側から入射する。
【００５３】
この実施例では、画面の法線に対して斜め方向から入射した斜め入射光を前記拡散層１３により拡散させて反射手段１４に入射させ、前記反射手段１４により反射された光を再び前記拡散層１３により拡散させるようにしているため、前記斜め方向から入射した光の反射光が、表示の観察方向である正面方向に向けて前記液晶セル１に入射させることができる。
【００５４】
なお、図２では便宜上、前記斜め入射光の反射手段１４までの入射経路を直線で示し、前記反射手段１４により反射された光のうち、正面方向に向かう正面反射光の経路を直線で示している。
【００５５】
前記液晶セル１にその後側から入射した反射光のうち、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}に入射し、表示の観察方向である正面方向に向かう正面反射光は、前記無電界画素Ａ_{（ＯＦＦ）}を透過して実質的に９０°旋光され、前側偏光板１０の透過軸に平行な直線偏光となり、その光が、前記二軸性位相差板１１を偏光状態をほとんど変えること無く透過し、さらに前記前側偏光板１０を透過して前側に出射する。
【００５６】
また、前記液晶セル１の電界印加画素Ａ_（ＯＮ）に入射した正面反射光は、前記電界印加画素Ａ_（ＯＮ）を複屈折作用をほとんど受けること無く透過し、さらに前記二軸性位相差板１１を偏光状態をほとんど変えること無く透過して、前側偏光板１０により吸収される。
【００５７】
このように、この液晶表示装置は、外光を利用する反射表示のときは、画面の法線付近の方向から入射し、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}を透過して反射手段１４により反射された正面反射光を、同じ無電界画素Ａ_{（ＯＦＦ）}を透過させて前側に出射させるとともに、前記画面の法線に対して斜め方向から入射し、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}または電界印加画素Ａ_（ＯＮ）を透過して反射手段１４により反射された光のうちの正面反射光をこの無電界画素Ａ_{（ＯＦＦ）}から前側に出射させる。また、前記画面の法線付近の方向から入射し、前記液晶セル１の電界印加画素Ａ_（ＯＮ）を透過した光が後側偏光板１２により吸収されるとともに、前記画面の法線に対して斜め方向から入射し、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}または電界印加画素Ａ_（ＯＮ）を透過して反射手段１４により反射された光のうちの正面反射光が電界印加画素Ａ_{（ＯＮ）の}前側偏光板１０により吸収される。
【００５８】
すなわち、この液晶表示装置は、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}による白の明表示（以下、白表示と言う）を、画面の法線付近の方向から前記無電界画素Ａ_{（ＯＦＦ）}を透過して入射し、反射手段１４により反射されて同じ無電界画素Ａ_{（ＯＦＦ）}を透過して前側に出射する光と、前記画面の法線に対して斜め方向から隣接する他の画素（無電界画素Ａ_{（ＯＦＦ）}及び電界印加画素Ａ_（ＯＮ））に入射し、前記反射手段１４により反射されて前記無電界画素Ａ_{（ＯＦＦ）}を透過して前側に出射する正面反射光とにより表示する。
【００５９】
また、この液晶表示装置は、前記液晶セル１の電界印加画素Ａ_（ＯＮ）による黒表示を、前記画面の法線付近の方向から入射し、前記電界印加画素Ａ_（ＯＮ）を透過した光の後側偏光板１２による吸収と、前記画面の法線に対して斜め方向から隣接する他の画素（無電界画素Ａ_{（ＯＦＦ）}及び電界印加画素Ａ_（ＯＮ））に入射し、前記反射手段１４により反射された光のうちの正面反射光を前記電界印加画素Ａ_（ＯＮ）の前側偏光板１０によって吸収することによって表示する。
【００６０】
そして、この液晶表示装置では、前記液晶セル１と前側偏光板１０との間に、画面の法線付近の方向から入射した光に対してはほとんど位相差を与えず、前記画面の法線に対して斜め方向から入射した光に対して位相差を与える二軸性位相差板１１を配置しているため、上述したように、表示の観察側である前側から前側偏光板１０により直線偏光とされて入射した光のうち、画面の法線付近の方向、つまり前記二軸性位相差板１１の屈折率が最も小さいｚ軸に沿った方向から入射した正面入射光は、前記二軸性位相差板１１を偏光状態をほとんど変えずに透過して前記液晶セル１に入射し、前記画面の法線に対して斜め方向、つまり前記二軸性位相差板１１のｚ軸に対して斜め方向から入射した斜め入射光は、前記二軸性位相差板１１により偏光状態を変えられて前記液晶セル１に入射する。
【００６１】
そのため、この液晶表示装置によれば、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}を透過した斜め入射光も、前記液晶セル１の電界印加画素Ａ_（ＯＮ）を透過した斜め入射光も、後側偏光板１２の透過軸に平行な直線偏光成分を含んだ偏光状態の光として前記後側偏光板１２に入射させ、この後側偏光板１２を透過した直線偏光を反射手段１４により反射させることができる。
【００６２】
しかも、この液晶表示装置では、前記液晶セル１のΔｎｄの値を３８０〜４２０ｎｍに設定し、前記二軸性位相差板１１の面内位相差（ｘ軸方向の屈折率ｎ_ｘとｙ軸方向の屈折率ｎ_ｙとの差）を２００〜３５０ｎｍ、Ｎｚ＝（ｎ_ｘ−ｎ_ｚ）／（ｎ_ｘ−ｎ_ｙ）の式で表わされるＮｚ係数を１．５以上とし、この二軸性位相差板１１を、前記ｘ軸を前記前側偏光板１０の吸収軸１０ａと実質的に平行にして配置しているため、前記無電界画素Ａ_{（ＯＦＦ）}を透過した斜め入射光も、前記電界印加画素Ａ_（ＯＮ）を透過した斜め入射光も、前記後側偏光板１２の透過軸に平行な直線偏光成分をより多い比率で含んだ偏光状態の光として前記後側偏光板１２に入射させ、より多くの光を前記後側偏光板１２を透過させて前記反射手段１４により反射させることができる。
【００６３】
そのため、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}に対応する白表示は、画面の法線付近の方向から前記無電界画素Ａ_{（ＯＦＦ）}を透過して入射した光の正面反射光（同じ無電界画素Ａ_{（ＯＦＦ）}を往復して透過して前側に出射する光）に、斜め方向から他の無電界画素Ａ_{（ＯＦＦ）}に入射した光の正面反射光が加えられた明るさである。
【００６４】
また、前記液晶セル１の電界印加画素に隣接した無電界画素に対応する明表示は、前記画面の法線付近の方向から前記無電界画素Ａ_{（ＯＦＦ）}を透過して入射した光の正面反射光に斜め方向から隣接した電界印加画素Ａ_（ＯＮ）に入射した光の正面反射光が加えられた明るさであり、この隣接した電界印加画素を透過して入射し、この電界印加画素に隣接する無電界画素を透過する正面反射光は充分な明るさをもった光である。
【００６５】
したがって、この液晶表示装置によれば、前記液晶セル１の電界印加画素Ａ_（ＯＮ）に斜め入射した光が吸収されることなく前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}から正面方向に出射するから、前記無電界画素Ａ_{（ＯＦＦ）}に対応する白表示部に前記電界印加画素Ａ_（ＯＮ）の影が生じることがなく、二重像の無い良好な品質の画像を表示することができる。
【００６６】
図３は、上記実施例の液晶表示装置から前記二軸性位相差板１１を省略した比較例の液晶表示装置の一部分のハッチングを省略した断面図であり、この比較例の液晶表示装置では、図に矢線で示したように、前側偏光板１０により直線偏光とされて液晶セル１に入射した光のうち、画面の法線付近の方向から入射して前記液晶セル１の電界印加画素Ａ_（ＯＮ）を透過した光が後側偏光板１２により吸収されるだけでなく、前記画面の法線に対して斜め方向から入射して前記液晶セル１の電界印加画素Ａ_（ＯＮ）を透過した光も後側偏光板１２により高い吸収率で吸収される。
【００６７】
すなわち、前記斜め方向から入射した光は、前記液晶セル１の液晶層９を斜めに透過するため、液晶分子９ａが基板２，３面に対して実質的に垂直に立ち上がり配向した電界印加画素Ａ_（ＯＮ）を透過するときに、液晶層９による複屈折作用を受けるが、その複屈折作用は僅かであるため、前記比較例では、画面の法線に対して斜め方向から入射して液晶セル１の電界印加画素Ａ_（ＯＮ）を透過した光も後側偏光板１２により高い吸収率で吸収される。
【００６８】
そのため、この比較例の液晶表示装置では、液晶セル１の無電界画素Ａ_{（ＯＦＦ）}に対応する白表示部に、斜め方向から入射する光の反射光が得られない領域ができ、、その領域が暗くなって、電界印加画素Ａ_（ＯＮ）の影ができる。
【００６９】
それに対し、前記二軸性位相差板１１を備えた上記実施例の液晶表示装置は、画面の法線に対して斜め方向から入射して液晶セル１の電界印加画素Ａ_（ＯＮ）を透過した光が後側偏光板１２を充分な透過率で透過する。
【００７０】
図４は、上記実施例と比較例の液晶表示装置の光の入射角（画面の法線に対する角度）と、液晶セル１の電界印加画素Ａ_（ＯＮ）に対応する黒表示部の透過率（以下、黒表示透過率と言う）の関係を示しており、ここでは、図１に示した１２時方位と３時方位からの光の入射角と黒表示透過率を示している。
【００７１】
なお、前記黒表示透過率は、前側偏光板１０の前側から入射した光の強度に対する後側偏光板１２を透過した光の強度の比である。また、図４において、−の入射角は、前記１２時方位及び３時方位に対して正反対の方位の入射角である。
【００７２】
図４のように、上記実施例の液晶表示装置も、二軸性位相差板１１を省略した比較例の液晶表示装置も、光の入射角が０°付近（画面の法線付近）であるときの黒表示透過率はほとんど０％であり、光の入射角が大きくなるのにともなって黒表示透過率が高くなるが、その度合は、１２時方位からの入射光に対しても、３時方位からの入射光に対しても、二軸性位相差板１１を備えた上記実施例の液晶表示装置の方が大きい。
【００７３】
すなわち、上記実施例の液晶表示装置は、二軸性位相差板１１を備えない比較例の液晶表示装置に比べて、画面の法線に対して斜め方向から入射して液晶セル１の電界印加画素Ａ_（ＯＮ）を透過した光を高い透過率で透過させる。
【００７４】
この透過光は反射手段１４により反射され、その反射光のうち、前記液晶セル１の電界印加画素Ａ_（ＯＮ）に入射した光が、この電界印加画素Ａ_（ＯＮ）と二軸性位相差板１１と前側偏光板１０とを透過して前側に出射する。
【００７５】
そのため、上記実施例の液晶表示装置は、電界印加画素Ａ_（ＯＮ）に隣接する無電界画素Ａ_{（ＯＦＦ）}から、画面の法線付近の方向から液晶セル１の無電界画素Ａ_{（ＯＦＦ）}を透過して入射した光の正面反射光と、斜め方向から前記液晶セル１の電界印加画素Ａ_（ＯＮ）に入射した光の正面反射光とが出射するため、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}に対応する白表示部に、前記電界印加画素Ａ_（ＯＮ）の影ができることはない。
【００７６】
なお、上記実施例の液晶表示装置は、画面の法線に対して斜め方向から液晶セル１の電界印加画素Ａ_（ＯＮ）に入射した光の透過率が高く、前記反射手段１４により反射されて前記電界印加画素Ａ_（ＯＮ）に入射する光の強度も高いが、表示の観察方向に出射する正面反射光は、前述したように前側偏光板１０により吸収されるため、前記電界印加画素Ａ_（ＯＮ）に対応する黒表示が明るくなることはない。
【００７７】
したがって、この液晶表示装置によれば、黒表示の周辺に影が生じることが無く、しかも前記黒表示の暗さと白表示の明るさがいずれも充分でコントラストの良い高品質の反射表示を行なうことができる。
【００７８】
しかも、前記比較例の液晶表示装置は、光の入射角が大きくなるのにともなって透過光が黄色味を帯びるため、前記無電界画素Ａ_{（ＯＦＦ）}に対応する白表示の帯色が目立つが、二軸性位相差板１１を備えた上記実施例の液晶表示装置は、前記白表示の帯色がほとんど目立たない。
【００７９】
すなわち、図５は、上記実施例と比較例の液晶表示装置の光の入射角と白表示の帯色度の関係を示しており、ここでは、図１に示した３時方位からの光を入射させたときの後側偏光板１２を透過した光の帯色度を示している。
【００８０】
なお、図５に示した帯色度は、前記透過光のうち、青の波長帯域の波長光の強度Ｂと、赤の波長帯域の波長光の強度Ｒ及び緑の波長帯域の波長光の強度Ｇとの比であり、（Ｇ＋Ｒ）／Ｂで表わされる値である。また、図５において、−の入射角は、前記３時方位に対して正反対の方位の入射角である。
【００８１】
図５のように、二軸性位相差板１１を備えない比較例の液晶表示装置は、光の入射角が大きくなるのにともなって（Ｇ＋Ｒ）／Ｂの値が大きくなり、透過光が黄色味を帯びる。
【００８２】
それに対して、二軸性位相差板１１を備えた上記実施例の液晶表示装置は、光の入射角が大きくなるのにともなって（Ｇ＋Ｒ）／Ｂの値が小さくなり、透過光が青色味を帯びるため、前記比較例の液晶表示装置の比べて、白表示の帯色がほとんど目立たない。
【００８３】
次に、前記反射手段１４の面光源１５から照明光を出射させて行なう透過表示について説明すると、この透過表示のときは、前記面光源１５から照明光が、後側偏光板１２により直線偏光とされ、さらに拡散層１３により拡散されて液晶セル１にその後側入射する。
【００８４】
前記液晶セル１にその後側から入射し、表示の観察方向である正面方向に向かう正面入射光のうち、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}に入射した光は、この無電界画素Ａ_{（ＯＦＦ）}を液晶層９の複屈折作用により実質的に９０°旋光されて透過して前側偏光板１０の透過軸に平行な直線偏光となり、前記液晶セル１の電界印加画素Ａ_（ＯＮ）に入射した光は、この電界印加画素Ａ_（ＯＮ）を液晶層９の複屈折作用をほとんど受けずに透過する。
【００８５】
そして、前記二軸性位相差板１１は、上述したように、屈折率が最も小さいｚ軸に沿った方向から入射した光に対してはほとんど位相差を与えないため、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}及び電界印加画素Ａ_（ＯＮ）を透過した正面入射光は、前記二軸性位相差板１１をほとんど偏光状態を変えること無く透過して前側偏光板１０に入射し、その光のうち、前記液晶セル１の無電界画素Ａ_{（ＯＦＦ）}を透過した光が前記前側偏光板１０を透過して前側に出射して白が表示され、前記液晶セル１の電界印加画素Ａ_（ＯＮ）を透過した光が前記前側偏光板１０により吸収されて黒が表示される。
【００８６】
このように、この実施例の液晶表示装置は、前記反射手段１４に、前側に照明光を出射する面光源１６を備えさせているため、上述した外光を利用する反射表示と、前記面光源１６からの照明光を利用する透過表示との両方の表示を行なうことができる。
【００８７】
前記面光源１６は、外光を利用する反射表示のときに補助光源として利用してもよく、反射表示のときに前記面光源１６からも照明光を出射させることにより、反射表示の明るさを上げることができる。
【００８８】
なお、上記実施例では、前記反射手段１４を、前記面光源１６の導光板１７の後面に反射膜１５を設けた構成としているが、反射手段は、半透過反射膜の後側に面光源を配置した構成としてもよい。
【００８９】
また、上記実施例の液晶表示装置は、外光を利用する反射表示と前記面光源１６からの照明光を利用する透過表示との両方の表示を行なうものであるが、この発明は、外光を利用する反射表示だけを行なう液晶表示装置にも適用することができ、その場合は、反射手段は反射膜だけでよい。
【００９０】
さらに、上記実施例では、液晶セル１と後側偏光板１２との間に拡散層１３を配置しているが、前記拡散層１３は、液晶セル１と反射手段１４との間であれば、前記後側偏光板１２の後側に配置してもよく、また、画面の法線に対して斜め方向から入射した光の反射光の一部を表示の観察方向である正面方向に向けて液晶セルに入射させるための反射手段は、例えば前記反射手段１４の反射膜１５を拡散反射膜とすることにより、反射手段に設けてもよい。
【００９１】
また、上記実施例では、前側偏光板１０を、その吸収軸１２ａを液晶セル１の前側基板２の近傍における液晶分子配向方向２ａと実質的に平行にして配置しているが、前記前側偏光板１０は、その透過軸を前記液晶セル１の前側基板２の近傍における液晶分子配向方向２ａと実質的に平行にして配置してもよい。
【００９２】
さらに、上記実施例の液晶表示装置は白黒画像を表示するものであるが、前記液晶セル１に複数の画素にそれぞれ対応させて複数の色、例えば赤、緑、青の３色のカラーフィルタを設け、カラー画像を表示するようにしてもよく、さらに前記液晶セル１は、アクティブマトリックス型に限らず、単純アクティブマトリックス型液晶セルでもよい。
【００９３】
【発明の効果】
この発明の液晶表示装置は、液晶層の液晶分子が実質的に９０°のツイスト角でツイスト配向した液晶セルの前側に、前側偏光板を、その吸収軸と透過軸のいずれか一方を前記液晶セルの前側基板の近傍における液晶分子配向方向と実質的に平行にして配置し、前記液晶セルの後側に、後側偏光板を、その吸収軸を前記前側偏光板の吸収軸に対して実質的に直交させて配置するとともに、前記液晶セルと前記前側偏光板との間に、光学的に二軸性を有するフィルムからなり、そのフィルム面に平行な面上に最も屈折率が大きいｘ軸とそれと直交するｙ軸を有し、これらの軸とそれぞれ直交する方向に最も屈折率が小さいｚ軸を有する二軸性位相差板を、前記ｘ軸を前記前側偏光板の吸収軸と実質的に平行にして配置し、さらに前記液晶セルのΔｎｄの値を３８０〜４２０ｎｍ、前記二軸性位相差板の前記ｘ軸方向の屈折率ｎ_ｘと前記ｙ軸方向の屈折率ｎ_ｙとの差を２００〜３５０ｎｍ、Ｎｚ＝（ｎ_ｘ−ｎ_ｚ）／（ｎ_ｘ−ｎ_ｙ）の式で表わされるＮｚ係数が１．５以上としたものであるため、前記液晶セルの電界印加画素に隣接した無電界画素に対応する明表示部に、前記電界印加画素の影が生じるのを防ぎ、二重像の無い良好な品質の画像を表示することができる。
【００９４】
この発明の液晶表示装置においては、前記液晶セルと反射手段との間または前記反射手段に光拡散手段を設けるのが好ましく、このようにすることにより、画面の法線に対して斜め方向から入射した光の反射光の一部を、表示の観察方向である正面方向に向けて前記液晶セルに入射させることができる。
【００９５】
また、この液晶表示装置において、前記反射手段は、前側に照明光を出射する面光源を備えているのが望ましく、このようにすることにより、外光を利用する反射表示と、前記面光源からの照明光を利用する透過表示との両方の表示を行なうことができる。
【図面の簡単な説明】
【図１】この発明の一実施例を示す液晶表示装置の分解斜視図。
【図２】前記液晶表示装置の一部分のハッチングを省略した断面図。
【図３】実施例の液晶表示装置から二軸性位相差板を省略した比較例の液晶表示装置の一部分のハッチングを省略した断面図。
【図４】実施例と比較例の液晶表示装置の光の入射角と電界印加画素に対応する黒表示部の透過率の関係を示す図。
【図５】実施例と比較例の液晶表示装置の光の入射角と白表示の帯色度の関係を示す図。
【符号の説明】
１…液晶セル
２，３…基板
５，６…電極
９…液晶層
９ａ…液晶分子
Ａ_{（ＯＦＦ）}…無電界画素
Ａ_（ＯＮ）…電界印加画素
１０…前側偏光板
１０ａ…吸収軸
１１…二軸性位相差板
１１ｘ…ｘ軸
１２…後側偏光板
１２ａ…吸収軸
１３…拡散層
１４…反射手段
１５…反射膜
１６…面光源[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device that performs reflection display using external light.
[0002]
[Prior art]
As a liquid crystal display device, a TN (twisted nematic) type is widely used.
[0003]
In this TN-type liquid crystal display device, electrodes for forming a plurality of pixels by mutually facing regions are formed on opposing inner surfaces of a front substrate that is a display observation side and a rear substrate that opposes the front substrate. A liquid crystal cell provided with a liquid crystal layer in which liquid crystal molecules are twisted substantially at a twist angle of 90 ° between these substrates; a front polarizer disposed in front of the liquid crystal cell; And a rear polarizing plate disposed on the rear side of the cell.
[0004]
In addition, there is a liquid crystal display device of a reflection type in which a reflection film is disposed on the rear side of the rear polarizing plate. The TN type reflection type liquid crystal display device has a structure in which the front polarizing plate passes through the absorption axis and the transmission axis thereof. Any one of the axes is arranged substantially parallel to the liquid crystal molecule alignment direction in the vicinity of the front substrate of the liquid crystal cell, and the rear polarizing plate has its absorption axis with respect to the absorption axis of the front polarizing plate. It is configured to be arranged substantially orthogonally.
[0005]
This reflection type liquid crystal display device performs reflection display using external light which is the light of the use environment. The reflection type liquid crystal display device enters the display from the front side which is the observation side of the display, is linearly polarized by the front side polarizing plate, and becomes a liquid crystal cell. Out of the light that has passed through the non-electric field pixels (pixels in which the liquid crystal molecules of the liquid crystal layer are in the initial twist alignment state) of the liquid crystal cell, and further transmitted through the rear polarizing plate and emitted to the rear side. The reflected light is reflected by the reflective film, and the reflected light is transmitted through the rear polarizer, the non-electric field pixel of the liquid crystal cell, and the front polarizer and is emitted to the front side, whereby a bright display (white display in the case of monochrome display) is obtained. Then, the light transmitted through the electric field applied pixels of the liquid crystal cell (pixels in which the liquid crystal molecules of the liquid crystal layer rise substantially vertically to the substrate surface) is absorbed by the rear polarizing plate to obtain a black display.
[0006]
[Problems to be solved by the invention]
In the reflection type liquid crystal display device, since external light is incident at various incident directions (directions around the normal to the screen) and incident angles, the bright display corresponding to the non-electric field pixel of the liquid crystal cell is performed on the screen (front polarization). (The front surface of the plate) from the direction near the normal to the light passing through the field-free pixel and entering, reflected by the reflective film, transmitted through the same field-free pixel and emitted to the front side, and the normal to the screen. The light is transmitted through another pixel from an oblique direction, enters, is reflected by the reflection film, is transmitted through the non-electric field pixel, and is emitted to the front side.
[0007]
On the other hand, the dark display corresponding to the electric field applied pixel of the liquid crystal cell is linearly polarized by the front polarizer and is incident on the liquid crystal cell, and is incident from a direction near the normal to the screen, and The display is performed by the light transmitted through the applied pixel being absorbed by the rear polarizing plate.
[0008]
However, in the conventional reflective liquid crystal display device, light incident obliquely with respect to the normal of the screen is transmitted through the electric field application pixels of the liquid crystal cell and then absorbed by the rear polarizer at a high absorption rate. Therefore, in the bright display portion corresponding to the non-electric field pixel adjacent to the electric field application pixel of the liquid crystal cell, a region where reflected light of the light incident from the oblique direction is not obtained is formed, and the region becomes dark and the electric field becomes dark. A shadow of the applied pixel is formed.
[0009]
Therefore, in the reflective liquid crystal display device, the original black display by the electric field application pixel and the shadow of the black display are observed as a double image, and the display image appears to be blurred or blurred.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide a reflection type liquid crystal display device capable of displaying a good quality image without a double image.
[0011]
[Means for Solving the Problems]
The liquid crystal display device of the present invention comprises:
Electrodes for forming a plurality of pixels are provided on the opposing inner surfaces of the front substrate, which is the display observation side, and the rear substrate, which opposes the front substrate, by opposing regions. A liquid crystal cell provided with a liquid crystal layer in which liquid crystal molecules are twisted substantially at a twist angle of 90 °, a front polarizer disposed on the front side of the liquid crystal cell, and the liquid crystal cell and the front polarizer. A retardation element disposed therebetween, a rear polarizing plate disposed on the rear side of the liquid crystal cell, and a reflection unit disposed on the rear side of the rear polarizing plate and reflecting light incident from the front side. Prepare,
The front polarizing plate is disposed so that one of the absorption axis and the transmission axis thereof is substantially parallel to the liquid crystal molecule alignment direction near the front substrate of the liquid crystal cell, and the rear polarizing plate has the absorption axis. Is arranged substantially orthogonal to the absorption axis of the front polarizing plate,
The value of the product Δnd of the refractive index anisotropy Δn of the liquid crystal of the liquid crystal cell and the thickness of the liquid crystal layer is set to 380 to 420 nm,
The retardation element is made of an optically biaxial film, and on a plane parallel to the film surface, the x-axis having the largest refractive index and the y-axis orthogonal to it are orthogonal to these axes, respectively. Direction, the refractive index of the z-axis is the smallest, and the refractive index in the x-axis direction is n. _x , The refractive index in the y-axis direction is n _y , The refractive index in the z-axis direction is n _z , The refractive index n in the x-axis direction _x And the refractive index n in the y-axis direction _y Is 200 to 350 nm, and Nz = (n _x -N _z ) / (N _x -N _y ) Is a biaxial retardation plate having an Nz coefficient of 1.5 or more, and the biaxial retardation plate has the x axis substantially equal to the absorption axis of the front polarizing plate. It is characterized by being arranged in parallel.
[0012]
This liquid crystal display device performs reflection display using external light which is light in the environment in which the liquid crystal display device is used, and displays a bright display corresponding to the non-electric field pixel of the liquid crystal cell on a screen (the front surface of the front polarizing plate). Light passing through the non-electric field pixel from a direction near the line, entering the same, and being reflected by the reflection means, transmitting through the same non-electric field pixel and exiting forward, and is adjacent to the normal of the screen from an oblique direction. The display is performed by light incident on the non-electric field pixel and the electric field application pixel, reflected by the reflection unit, transmitted through the non-electric field pixel and emitted to the front side, and black display corresponding to the electric field application pixel of the liquid crystal cell is performed. Light that is incident from a direction near the normal to the screen and transmitted through the pixel applied with electric field is absorbed by the rear polarizer, and is the front reflected light of the light reflected by the reflection unit (the direction near the normal to the screen). ) Passes through the electric field application pixel. After displays by being absorbed by the front polarizer.
[0013]
In this liquid crystal display device, since the biaxial retardation plate is disposed between the liquid crystal cell and the front-side polarizing plate, the light is input as linearly polarized light by the front-side polarizing plate from the front side, which is the display observation side. Of the light, front incident light incident from a direction near the normal to the screen, that is, a direction along the z-axis, where the refractive index of the biaxial retardation plate is the smallest, polarizes the biaxial retardation plate. The obliquely incident light transmitted through the liquid crystal cell with almost no change in state and incident on the liquid crystal cell in an oblique direction with respect to the normal of the screen, that is, an oblique direction with respect to the z axis of the biaxial retardation plate is The polarization state is changed by the biaxial retardation plate, and the light enters the liquid crystal cell.
[0014]
Therefore, according to this liquid crystal display device, neither the oblique incident light transmitted through the non-electric field pixel of the liquid crystal cell nor the oblique incident light transmitted through the electric field applied pixel of the liquid crystal cell is parallel to the transmission axis of the rear polarizer. The light in the polarization state containing the linearly polarized light component is made incident on the rear polarizing plate, and the linearly polarized light transmitted through the rear polarizing plate can be reflected by the reflection means.
[0015]
Moreover, in this liquid crystal display device, the value of Δnd of the liquid crystal cell is set to 380 to 420 nm, and the refractive index n of the biaxial retardation plate in the x-axis direction is set. _x And the refractive index n in the y-axis direction _y Is 200 to 350 nm, and Nz = (n _x -N _z ) / (N _x -N _y )) Is set to 1.5 or more, and the biaxial retardation plate is arranged with the x-axis substantially parallel to the absorption axis of the front polarizing plate. Both the oblique incident light transmitted through the electric field pixel and the oblique incident light transmitted through the electric field applied pixel are converted into light in a polarization state including a linear polarization component parallel to the transmission axis of the rear polarizer at a higher ratio. The light can be made incident on the side polarizing plate, and more light can be transmitted through the rear polarizing plate and reflected by the reflecting means.
[0016]
Therefore, the bright display corresponding to the non-electric field pixel of the liquid crystal cell is a front reflection light of light that has been transmitted through the non-electric field pixel from a direction near the normal of the screen (the light is transmitted back and forth through the same non-electric field pixel). This is the brightness obtained by adding the front-reflected light of the light that has passed through another non-electric field pixel and entered from an oblique direction. In addition, the bright display corresponding to the non-electric field pixel adjacent to the electric field application pixel is the same as the front reflection light of the light transmitted through the non-electric field pixel and incident from the direction near the normal line of the screen, and is adjacent to the oblique direction. This is the brightness to which the front reflected light of the light that has passed through and entered the electric field applying pixel has been added, transmitted through the adjacent electric field applying pixel, entered, and transmitted through the non-electric field pixel adjacent to the electric field applying pixel. The front reflected light is light having sufficient brightness.
[0017]
Therefore, according to this liquid crystal display device, light obliquely incident on the electric field application pixel of the liquid crystal cell is emitted from the non-electric field pixel of the liquid crystal cell in the front direction without being absorbed. The shadow of the electric field application pixel does not appear on the bright display portion, and a high quality image without a double image can be displayed.
[0018]
As described above, in the liquid crystal display device of the present invention, the front polarizing plate is provided with one of the absorption axis and the transmission axis on the front side of the liquid crystal cell in which the liquid crystal molecules of the liquid crystal layer are substantially twisted at a twist angle of 90 °. Is disposed substantially parallel to the liquid crystal molecule orientation direction in the vicinity of the front substrate of the liquid crystal cell, and on the rear side of the liquid crystal cell, the rear polarizing plate has its absorption axis with respect to the absorption axis of the front polarizing plate. Substantially orthogonal to each other, and with a reflection means disposed behind the rear polarizing plate, between the liquid crystal cell and the front polarizing plate, an optically biaxial film. A biaxial retardation having an x-axis with the largest refractive index and a y-axis orthogonal to it on a plane parallel to the film plane, and a z-axis with the smallest refractive index in a direction orthogonal to these axes, respectively. Plate, the x-axis is the absorption axis of the front polarizer Substantially arranged in parallel, further 380~420nm the value of Δnd of the liquid crystal cell, the refractive index of the x-axis direction of the biaxial retardation plate n _x And the refractive index n in the y-axis direction _y Is 200 to 350 nm, and Nz = (n _x -N _z ) / (N _x -N _y By setting the Nz coefficient represented by the formula of 1.5 or more to 1.5, the front reflected light of the obliquely incident light transmitted through the electric field application pixel of the liquid crystal cell is displayed on the bright display portion corresponding to the non-electric field pixel of the liquid crystal cell. To prevent the shadow of the electric field application pixel from being generated, and to display an image of good quality without a double image.
[0019]
In the liquid crystal display device according to the present invention, the biaxial retardation plate is made of, for example, a biaxially stretched film of polycarbonate.
[0020]
In this liquid crystal display device, it is preferable that a light diffusing unit is provided between the liquid crystal cell and the reflecting unit or in the reflecting unit.
[0021]
Further, it is preferable that the reflection means includes a surface light source for emitting illumination light on the front side.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an exploded perspective view of the liquid crystal display device of this embodiment, and FIG. 2 is a cross-sectional view of the liquid crystal display device with a part of the liquid crystal display device omitted from hatching.
[0023]
As shown in FIGS. 1 and 2, the liquid crystal display device of this embodiment includes a liquid crystal cell 1, a front polarizing plate 10 disposed in front of the liquid crystal cell 1, a liquid crystal cell 1 and a front polarizing plate 10. , A rear polarizer 12 disposed on the rear side of the liquid crystal cell 1, and a light diffuser provided between the liquid crystal cell 1 and the rear polarizer 12. It comprises a layer (hereinafter referred to as a diffusion layer) 13 and a reflecting means 14 disposed on the rear side of the rear polarizing plate 12 and reflecting light incident from the front side.
[0024]
In the display cell 1, a front transparent substrate 2, which is a display observation side, and a rear transparent substrate 3 facing the front substrate 2 are joined via a frame-shaped sealing material 4, and these substrates 2 , 3 are respectively provided with transparent electrodes 5, 6 for forming a plurality of pixels A by regions facing each other, and the sealing material between the front substrate 2 and the rear substrate 3 is provided. The liquid crystal layer 9 is provided in a region surrounded by 4.
[0025]
In the liquid crystal cell 1, a single-film counter electrode 5 is provided on the inner surface of the front substrate 2, and a plurality of pixel electrodes 6 arranged in a matrix in the row and column directions on the inner surface of the rear substrate 3 are provided. The active matrix type liquid crystal cell is provided. Although not shown in the figure, a plurality of TFTs (thin film transistors) connected to the plurality of pixel electrodes 6 and a TFT in each row are formed on the inner surface of the rear substrate 3. And a plurality of data lines for supplying data signals to the TFTs in each column.
[0026]
The liquid crystal molecules 9a of the liquid crystal layer 9 of the liquid crystal cell 1 are aligned in the vicinity of the substrates 2 and 3 by the alignment films 7 and 8 provided on the inner surfaces of the front and rear substrates 2 and 3 so as to cover the electrodes 5 and 6. The direction is defined, and the substrates 2 and 3 are twist-oriented at a twist angle of substantially 90 °.
[0027]
That is, as shown in FIG. 1, the liquid crystal molecule orientation direction 2a in the vicinity of the front substrate 2 of the liquid crystal cell 1 is, for example, 45 degrees counterclockwise as viewed from the front with respect to the horizontal axis O of the screen (the front surface of the front polarizing plate). The liquid crystal molecule orientation direction 3a near the rear substrate 3 is at a right angle of 45 ° with respect to the horizontal axis O when viewed from the front, and the liquid crystal molecules 9a of the liquid crystal layer 9 are As indicated by the dashed arrow, the twist direction is from the rear substrate 3 to the front substrate 2 and twisted clockwise substantially at a 90 ° twist angle when viewed from the front.
[0028]
FIG. 2 shows a state in which an electric field is applied between the electrodes 5 and 6 of some pixels A of the liquid crystal cell 1 so that the liquid crystal molecules 9a rise and become substantially perpendicular to the substrates 2 and 3. Is shown.
[0029]
The value of the product Δnd of the refractive index anisotropy Δn of the liquid crystal of the liquid crystal cell 1 and the thickness of the liquid crystal layer (the value with respect to the incident light from the normal direction of the screen) is a wavelength of 550 nm which is an intermediate wavelength in the visible light band. It is set in the range of 380 to 420 nm for light.
[0030]
The front polarizing plate 10 has one of the absorption axis 10 a and the transmission axis (not shown), for example, the absorption axis 10 a substantially aligned with the liquid crystal molecule alignment direction 2 a in the vicinity of the front substrate 2 of the liquid crystal cell 1. (In a direction of 45 ° counterclockwise when viewed from the front with respect to the horizontal axis O of the screen), and the rear polarizing plate 12 moves its absorption axis 12 a to the front polarizing plate 10. Are arranged in a direction substantially perpendicular to the absorption axis 10a (a direction 135 ° counterclockwise as viewed from the front with respect to the horizontal axis O of the screen).
[0031]
Further, the retardation element 11 disposed between the liquid crystal cell 1 and the front polarizing plate 10 is made of an optically biaxial film, and has a refractive index of the highest on a plane parallel to the film plane. It is a biaxial retardation plate having a large x-axis and a y-axis orthogonal thereto, and a z-axis having the smallest refractive index in a direction orthogonal to these axes, for example, a biaxially stretched film of polycarbonate. I have.
[0032]
The biaxial retardation plate 11 has a refractive index in the x-axis direction of n _x , The refractive index in the y-axis direction is n _y , The refractive index in the z-axis direction is n _z , The refractive index n in the x-axis direction _x And the refractive index n in the y-axis direction _y (Hereinafter referred to as in-plane phase difference) in the range of 200 to 350 nm for 550 nm wavelength light, and Nz = (n _x -N _z ) / (N _x -N _y ) Has the characteristic that the Nz coefficient is 1.5 or more.
[0033]
As shown in FIG. 1, the biaxial retardation plate 11 has its x-axis 11x having the largest refractive index oriented in a direction substantially parallel to the absorption axis 10a of the front polarizer 10 (the horizontal axis of the screen). O (in a direction of 45 ° counterclockwise when viewed from the front side).
[0034]
On the other hand, the reflecting means 14 includes a specular reflection film 15 disposed opposite to the rear surface of the rear polarizing plate 12 and a surface light source 16 provided in front of the reflection film 15 and emitting illumination light to the front side. Consists of
[0035]
The surface light source 16 is formed of a transparent plate such as an acrylic resin plate, and has a light guide plate 17 having one end surface serving as an incident end surface through which light is incident, and a light emission provided to face the incident end surface of the light guide plate 17. The reflection film is formed on the rear surface of the light guide plate 17 by vapor deposition or plating.
[0036]
In addition, the surface light source 16 used in this embodiment has a plurality of light emitting elements 18 composed of LEDs (light emitting diodes) arranged so as to face the incident end face of the light guide plate 17. The light-emitting element arranged to face the end face may be a straight-tube cold-cathode tube or the like.
[0037]
The reflecting means 14 is configured such that light incident from the front side of the light guide plate 17 of the surface light source 16 passes through the light guide plate 17 and is reflected by the reflection film 15, and emits the reflected light to the front side of the light guide plate 16. When the light emitting element 18 of the surface light source 16 is turned on, the illumination light emitted from the light emitting element 18 is guided by the light guide plate 16 and emitted from the front surface to the front side. Is incident on the light guide plate 17 from the incident end face thereof, and is reflected by the reflection film 15 provided on the rear surface of the light guide plate 17 and at the interface between the front surface of the light guide plate 17 and the outside air (air). The light is diffused and guided into the light guide plate 17 while repeating the total reflection, and is emitted from the entire front surface of the light guide plate 17.
[0038]
The liquid crystal display device of this embodiment performs reflection display using external light that is light of the use environment under a use environment with sufficient illuminance, and when external light with sufficient brightness cannot be obtained, The illumination light is emitted from the surface light source 16 of the reflection means 14 to perform transmissive display, and the display is viewed from the front (a direction near the normal to the screen).
[0039]
First, a description will be given of a reflection display using external light. As shown by an arrow in FIG. 2, external light is applied from various angles of incidence (directions around the normal to the screen) from the front side, which is the viewing side of the display. Then, the light is incident at an incident angle, and the polarized component parallel to the absorption axis 10a is absorbed by the front polarizing plate 10, and becomes linearly polarized light parallel to the transmission axis of the front polarizing plate 10 to the biaxial retardation plate 11. Incident.
[0040]
As described above, the biaxial retardation plate 11 is made of an optically biaxial film, and the x-axis having the largest refractive index and the y-axis orthogonal to the x-axis are formed on a plane parallel to the film plane. Axis, and has a z-axis with the smallest refractive index in a direction orthogonal to each of these axes, so that the light incident from a direction along the z-axis with the smallest refractive index is almost invisible. No phase difference is given, and a phase difference is given to light incident from a direction oblique to the z-axis.
[0041]
Therefore, of the light that is linearly polarized by the front polarizer 10 and enters the biaxial retardation plate 11, the direction along the normal line of the screen, that is, the z-axis of the biaxial retardation plate 11 Is incident on the liquid crystal cell 1 through the biaxial retardation plate 11 with almost no change in the polarization state.
[0042]
Of the front incident light that has entered the liquid crystal cell 1, the non-electric field pixel A of the liquid crystal cell 1 _(OFF) That is, the light that has entered the pixel in which the liquid crystal molecules 9a of the liquid crystal layer 9 are in the initial twisted state is the non-electric field pixel _(OFF) Is substantially rotated by 90 ° due to the birefringence action of the liquid crystal layer 9 and is transmitted therethrough, and becomes linearly polarized light parallel to the transmission axis (not shown) of the rear polarizing plate 12. Then, the light enters the rear polarizing plate 12, passes through the rear polarizing plate 12, and is reflected by the reflection unit 14.
[0043]
The reflected light reflected by the reflection means 14 passes through the rear polarizing plate 12 again, is further diffused by the diffusion layer 13 and enters the liquid crystal cell 1 from the rear side.
[0044]
Then, of the reflected light incident on the liquid crystal cell 1 from the rear side, the front reflected light traveling in the front direction which is the display observation direction is the non-electric field pixel A transmitted through the above-described incident path from the front side. _(OFF) And the non-electric field pixel A _(OFF) , And is rotated by substantially 90 °, becomes linearly polarized light parallel to the transmission axis (not shown) of the front polarizing plate 10, and the light almost changes the polarization state of the biaxial retardation plate 11. Without being transmitted, and further transmitted through the front polarizing plate 10 and emitted to the front side.
[0045]
On the other hand, of the front incident light incident on the liquid crystal cell 1, the electric field application pixel A of the liquid crystal cell 1 _(ON) That is, the light incident on the pixel in which the liquid crystal molecules 9a of the liquid crystal layer 9 rise and are oriented substantially perpendicularly to the surfaces of the substrates 2 and 3 is reflected by the electric field applied pixel A _(ON) Is transmitted with little birefringence of the liquid crystal layer 9, transmitted through the diffusion layer 13 and absorbed by the rear polarizer 12. In FIG. 2, ● indicates light absorption.
[0046]
Also, of the light that has been linearly polarized by the front polarizer 10 and incident on the biaxial retardation plate 11, the z axis of the biaxial retardation plate 11 is inclined with respect to the normal to the screen. The obliquely incident light incident from the oblique direction with respect to the axis is given a phase difference between the ordinary light and the extraordinary light by the biaxial retardation plate 11, changes the polarization state, and enters the liquid crystal cell 1.
[0047]
The polarization state of the obliquely incident light transmitted through the biaxial retardation plate 11 varies depending on the incident angle on the biaxial retardation plate 11, and the incident angle (the angle of the biaxial retardation plate 11 with respect to the z axis). ) Increases, the change in the polarization state from the linearly polarized light increases.
[0048]
The obliquely incident light that has entered the liquid crystal cell 1 is a non-electric field pixel (a pixel in which the liquid crystal molecules 9a are in the initial twist alignment state) A of the liquid crystal cell 1. _(OFF) Or an electric field applied pixel (a pixel in which liquid crystal molecules 9a rise and align substantially perpendicular to the substrates 2 and 3) A _(ON) Is transmitted by further changing the polarization state by the birefringence action of the liquid crystal layer 9.
[0049]
That is, since the obliquely incident light is transmitted obliquely through the liquid crystal layer 9 of the liquid crystal cell 1, the non-electric field pixels A _(OFF) Obliquely incident light incident on the non-electric field pixel A _(OFF) The liquid crystal layer 9 undergoes a birefringence action different from the above-described front incident light to change the polarization state, and the electric field applied pixel A _(ON) Obliquely incident light incident on the electric field application pixel A _(ON) Of the liquid crystal layer 9 to change the polarization state.
[0050]
The polarization state of the liquid crystal cell 1 is changed by passing through the biaxial retardation plate 11, and the pixel A _(OFF) Or electric field applied pixel A _(ON) The oblique incident light that has passed through and changed the polarization state is diffused by the diffusion layer 13 and enters the rear polarizing plate 12, of which light parallel to the absorption axis 12 a of the rear polarizing plate 12. The polarized light component is absorbed by the rear polarizing plate 12, and linearly polarized light (light having a polarization component parallel to the transmission axis of the rear polarizing plate 12) transmitted through the rear polarizing plate 12 passes through the rear polarizing plate 12. The light is transmitted and reflected by the reflection means 14.
[0051]
Electroless field pixel A of the liquid crystal cell 1 _(OFF) Obliquely incident light transmitted through the liquid crystal cell 1 and the electric field application pixel A of the liquid crystal cell 1 _(ON) Are obliquely incident light having different polarization states, and therefore, these obliquely incident light are transmitted through the rear polarizer 12 with different transmittances and are reflected by the reflection means 14.
[0052]
The reflected light reflected by the reflection means 14 passes through the rear polarizing plate 12 again, is further diffused by the diffusion layer 13 and enters the liquid crystal cell 1 from the rear side.
[0053]
In this embodiment, light obliquely incident on the screen normal is diffused by the diffusion layer 13 to be incident on the reflection means 14, and the light reflected by the reflection means 14 is again reflected by the diffusion layer. 13, the reflected light of the light incident from the oblique direction can be incident on the liquid crystal cell 1 in the front direction, which is the display observation direction.
[0054]
In FIG. 2, for convenience, the incident path of the obliquely incident light to the reflection means 14 is indicated by a straight line, and the path of the front reflected light toward the front direction of the light reflected by the reflection means 14 is indicated by a straight line. I have.
[0055]
Of the reflected light incident on the liquid crystal cell 1 from the rear side, the non-electric field pixel A of the liquid crystal cell 1 _(OFF) And the front reflected light traveling in the front direction, which is the viewing direction of the display, _(OFF) , And is rotated by substantially 90 °, becomes linearly polarized light parallel to the transmission axis of the front polarizing plate 10, and the light is transmitted through the biaxial retardation plate 11 without substantially changing the polarization state. The light passes through the front polarizing plate 10 and is emitted to the front.
[0056]
The electric field application pixel A of the liquid crystal cell 1 _(ON) Is reflected from the electric field applying pixel A _(ON) Is transmitted through the biaxial retardation plate 11 without substantially changing the polarization state, and is absorbed by the front polarizing plate 10.
[0057]
As described above, in the liquid crystal display device, in the case of the reflection display using the external light, the light is incident from a direction near the normal of the screen, and the non-electric field pixel A of the liquid crystal cell 1 is used. _(OFF) Is reflected by the reflection means 14 and transmitted to the same non-electric field pixel A. _(OFF) Is transmitted and emitted to the front side, and is incident from an oblique direction with respect to the normal line of the screen. _(OFF) Or electric field applied pixel A _(ON) Out of the light transmitted through and reflected by the reflection means 14, _(OFF) From the front side. Further, the light is incident from a direction near the normal to the screen, and the electric field applied pixel A of the liquid crystal cell 1 is _(ON) Is absorbed by the rear polarizer 12 and is incident obliquely with respect to the normal of the screen, and the non-electric field pixels A of the liquid crystal cell 1 _(OFF) Or electric field applied pixel A _(ON) Of the light transmitted through and reflected by the reflection means 14 is reflected by the electric field application pixel A. _(ON) It is absorbed by the front polarizer 10.
[0058]
In other words, this liquid crystal display device has no electric field pixels A of the liquid crystal cell 1. _(OFF) White display (hereinafter referred to as white display) by the non-electric field pixel A from the direction near the normal line of the screen. _(OFF) , And is reflected by the reflecting means 14 to be the same non-electric field pixel A _(OFF) And the other pixel adjacent to the normal line of the screen obliquely with respect to the normal line (the non-electric field pixel A _(OFF) And electric field applied pixel A _(ON) ), Is reflected by the reflection means 14 and is reflected by the non-electric field pixel A. _(OFF) And front reflected light emitted to the front side after passing through the display.
[0059]
Further, the liquid crystal display device has an electric field applied pixel A of the liquid crystal cell 1. _(ON) From the direction near the normal to the screen, and the electric field applied pixel A _(ON) Is absorbed by the rear polarizer 12 and the other pixels adjacent to the normal line of the screen obliquely from the normal line (the non-electric field pixels A _(OFF) And electric field applied pixel A _(ON) ), And the front reflected light of the light reflected by the reflection means 14 is converted to the electric field applied pixel A. _(ON) Is displayed by absorption by the front polarizing plate 10 of FIG.
[0060]
In this liquid crystal display device, there is almost no phase difference between the liquid crystal cell 1 and the front polarizer 10 with respect to light incident from a direction near the normal to the screen. Since the biaxial retardation plate 11 that gives a phase difference to light incident from an oblique direction is disposed, as described above, linear polarization is performed by the front polarizer 10 from the front side, which is the display observation side. Out of the incident light, the front incident light incident from the direction near the normal of the screen, that is, the direction along the z-axis where the refractive index of the biaxial retardation plate 11 is the smallest, is the biaxial position. The light passes through the phase difference plate 11 with almost no change in the polarization state and enters the liquid crystal cell 1, and is oblique to the normal of the screen, that is, oblique to the z-axis of the biaxial phase difference plate 11. Obliquely incident light from the biaxial retardation plate 11 It can change the polarization state incident on the liquid crystal cell 1.
[0061]
Therefore, according to this liquid crystal display device, the non-electric field pixel A of the liquid crystal cell 1 _(OFF) Obliquely incident light that has passed through the _(ON) Obliquely incident light transmitted through the rear polarizing plate 12 is also incident on the rear polarizing plate 12 as light in a polarization state including a linearly polarized component parallel to the transmission axis of the rear polarizing plate 12, The polarized light can be reflected by the reflection means 14.
[0062]
Moreover, in this liquid crystal display device, the value of Δnd of the liquid crystal cell 1 is set to 380 to 420 nm, and the in-plane retardation (refractive index n in the x-axis direction) of the biaxial retardation plate 11 is set. _x And the refractive index n in the y-axis direction _y ) = 200-350 nm, Nz = (n _x -N _z ) / (N _x -N _y ), The Nz coefficient is set to 1.5 or more, and the biaxial retardation plate 11 is arranged with the x-axis substantially parallel to the absorption axis 10a of the front polarizing plate 10. The non-electric field pixel A _(OFF) Obliquely incident light that has passed through the _(ON) Obliquely incident light transmitted through the rear polarizing plate 12 is also incident on the rear polarizing plate 12 as light in a polarization state including a linear polarization component parallel to the transmission axis of the rear polarizing plate 12 at a higher ratio, and more light is emitted. The light can pass through the rear polarizing plate 12 and be reflected by the reflecting means 14.
[0063]
Therefore, the non-electric field pixel A of the liquid crystal cell 1 _(OFF) Is displayed from the direction near the normal of the screen. _(OFF) Reflected light (the same non-electric field pixel A _(OFF) Is transmitted and reciprocated through, and is emitted to the front side). _(OFF) Is the brightness to which the front reflected light of the light incident on the light source is added.
[0064]
The bright display corresponding to the non-electric field pixel adjacent to the electric field application pixel of the liquid crystal cell 1 is performed in the direction near the normal line of the screen. _(OFF) Field applying pixel A adjacent to the front reflected light of the light that has passed through the _(ON) This is the brightness to which the front reflected light of the incident light is added. The front reflected light transmitted through the adjacent electric field application pixel and enters, and transmitted through the non-electric field pixel adjacent to the electric field applied pixel is sufficiently bright. It is a light that has a strong feeling.
[0065]
Therefore, according to this liquid crystal display device, the electric field application pixel A of the liquid crystal cell 1 _(ON) Field-free pixels A of the liquid crystal cell 1 without the light obliquely incident on _(OFF) Out of the pixel in the front direction. _(OFF) The electric field applying pixel A is provided on the white display portion corresponding to _(ON) The image of good quality without a double image can be displayed without the occurrence of shadows.
[0066]
FIG. 3 is a cross-sectional view of the liquid crystal display device of the above embodiment, in which the hatching of a part of the liquid crystal display device of the comparative example in which the biaxial retardation plate 11 is omitted is omitted. As shown by the arrow in the drawing, of the light that has been linearly polarized by the front polarizer 10 and incident on the liquid crystal cell 1, the light is incident from a direction near the normal to the screen and the electric field applied pixel A of the liquid crystal cell 1 _(ON) Is not only absorbed by the rear polarizer 12 but also incident obliquely with respect to the normal of the screen and the electric field applied pixel A of the liquid crystal cell 1 _(ON) Is also absorbed by the rear polarizing plate 12 at a high absorption rate.
[0067]
That is, since the light incident from the oblique direction is transmitted obliquely through the liquid crystal layer 9 of the liquid crystal cell 1, the electric field applying pixel A in which the liquid crystal molecules 9a rise and are oriented substantially perpendicularly to the substrates 2 and 3 planes. _(ON) When the light passes through the liquid crystal layer 9, the liquid crystal layer 9 undergoes a birefringence effect. However, the birefringence effect is slight. Applied pixel A _(ON) Is also absorbed by the rear polarizing plate 12 at a high absorption rate.
[0068]
Therefore, in the liquid crystal display device of this comparative example, the non-electric field pixel A of the liquid crystal cell 1 _(OFF) Is formed in the white display portion corresponding to the area where reflected light of light incident from an oblique direction cannot be obtained. _(ON) There is a shadow.
[0069]
On the other hand, in the liquid crystal display device of the above-described embodiment including the biaxial retardation plate 11, the electric field applied pixel A of the liquid crystal cell 1 is incident obliquely with respect to the screen normal. _(ON) Pass through the rear polarizing plate 12 with a sufficient transmittance.
[0070]
FIG. 4 shows the incident angles of light (the angles with respect to the normal to the screen) of the liquid crystal display devices of the above embodiment and the comparative example, and the electric field applied pixels A of the liquid crystal cell 1. _(ON) 1 shows the relationship between the transmittance of the black display portion (hereinafter, referred to as black display transmittance) corresponding to the angle of incidence of the light from the 12 o'clock direction and the 3 o'clock direction shown in FIG. The transmittance is shown.
[0071]
The black display transmittance is the ratio of the intensity of light transmitted through the rear polarizing plate 12 to the intensity of light incident from the front side of the front polarizing plate 10. In FIG. 4, the negative incident angle is an incident angle in a direction directly opposite to the 12:00 and 3 o'clock directions.
[0072]
As shown in FIG. 4, in both the liquid crystal display device of the above embodiment and the liquid crystal display device of the comparative example in which the biaxial retardation plate 11 is omitted, the incident angle of light is around 0 ° (around the normal to the screen). At this time, the black display transmittance is almost 0%, and the black display transmittance increases as the incident angle of the light increases. The liquid crystal display device of the above embodiment including the biaxial retardation plate 11 is also larger for incident light from the time direction.
[0073]
That is, the liquid crystal display device of the above-described embodiment is incident on the liquid crystal cell 1 obliquely with respect to the normal of the screen and applies an electric field to the liquid crystal cell 1 as compared with the liquid crystal display device of the comparative example without the biaxial retardation plate 11. Pixel A _(ON) Is transmitted at a high transmittance.
[0074]
The transmitted light is reflected by the reflection means 14, and among the reflected light, the electric field application pixel A of the liquid crystal cell 1 _(ON) Incident on the electric field applying pixel A _(ON) Then, the light passes through the biaxial retardation plate 11 and the front polarizing plate 10 and is emitted to the front side.
[0075]
For this reason, the liquid crystal display device of the above embodiment has the electric field applied pixel A _(ON) Field-free pixel A adjacent to _(OFF) From the direction near the normal of the screen to the non-electric field pixel A of the liquid crystal cell 1. _(OFF) And the electric field applied pixels A of the liquid crystal cell 1 from the oblique direction. _(ON) Of the liquid crystal cell 1 and the front reflection light of the light incident on the _(OFF) The electric field applied pixel A _(ON) There is no shadow.
[0076]
In the liquid crystal display device of the above embodiment, the electric field applied pixel A of the liquid crystal cell 1 is obliquely oblique to the screen normal. _(ON) The light incident on the pixel A is reflected by the reflection means 14 and reflected by the electric field application pixel A. _(ON) Although the intensity of the light incident on the field-applied pixel A is high, the front reflected light emitted in the viewing direction of the display is absorbed by the front polarizer 10 as described above. _(ON) Does not become brighter.
[0077]
Therefore, according to this liquid crystal display device, there is no shadow around the black display, and both the darkness of the black display and the brightness of the white display are sufficient, and a high-quality reflective display with good contrast can be performed. Can be.
[0078]
Moreover, in the liquid crystal display device of the comparative example, the transmitted light takes on a yellow tint as the incident angle of light increases, so that the non-electric field pixels A _(OFF) However, in the liquid crystal display device of the above-described embodiment including the biaxial retardation plate 11, the white display band is almost inconspicuous.
[0079]
That is, FIG. 5 shows the relationship between the incident angle of light and the chromaticity of white display of the liquid crystal display devices of the above embodiment and the comparative example. Here, light from the 3 o'clock direction shown in FIG. It shows the chromaticity of light transmitted through the rear polarizing plate 12 when it is incident.
[0080]
The chromaticity shown in FIG. 5 indicates the intensity B of the wavelength light in the blue wavelength band, the intensity R of the wavelength light in the red wavelength band, and the intensity of the wavelength light in the green wavelength band in the transmitted light. This is a ratio to G, and is a value represented by (G + R) / B. In FIG. 5, the negative angle of incidence is the angle of incidence in the direction exactly opposite to the 3 o'clock direction.
[0081]
As shown in FIG. 5, in the liquid crystal display device of the comparative example having no biaxial retardation plate 11, the value of (G + R) / B increases as the incident angle of light increases, and the transmitted light is yellow. Taste.
[0082]
On the other hand, in the liquid crystal display device of the above embodiment including the biaxial retardation plate 11, the value of (G + R) / B decreases as the incident angle of light increases, and the transmitted light has a blue tint. Therefore, the white display color is hardly noticeable as compared with the liquid crystal display device of the comparative example.
[0083]
Next, transmission display performed by emitting illumination light from the surface light source 15 of the reflection means 14 will be described. In this transmission display, the illumination light from the surface light source 15 is converted into linearly polarized light by the rear polarizing plate 12. Then, the light is further diffused by the diffusion layer 13 and enters the liquid crystal cell 1 on the rear side.
[0084]
Of the front incident light that enters the liquid crystal cell 1 from the rear side and travels in the front direction which is the viewing direction of display, the non-electric field pixel A of the liquid crystal cell 1 _(OFF) Incident on the non-electric field pixel A _(OFF) Is rotated by substantially 90 ° due to the birefringence effect of the liquid crystal layer 9 and transmitted to become linearly polarized light parallel to the transmission axis of the front polarizer 10. _(ON) Incident on the pixel A _(ON) Is transmitted with little birefringence of the liquid crystal layer 9.
[0085]
As described above, since the biaxial retardation plate 11 hardly gives a phase difference to light incident from the direction along the z-axis having the smallest refractive index, the biaxial retardation plate 11 Electric field pixel A _(OFF) And electric field applied pixel A _(ON) Is transmitted through the biaxial retardation plate 11 with almost no change in the polarization state and is incident on the front-side polarizing plate 10. Among the light, the non-electric field pixel A of the liquid crystal cell 1 _(OFF) Is transmitted through the front-side polarizing plate 10 and is emitted to the front side to display white, and the electric field applied pixel A of the liquid crystal cell 1 is displayed. _(ON) Is transmitted by the front polarizer 10 and black is displayed.
[0086]
As described above, in the liquid crystal display device of this embodiment, since the reflecting means 14 is provided with the surface light source 16 for emitting illumination light on the front side, the reflection display using the external light described above and the surface light source It is possible to perform both display and transmission display using the illumination light from 16.
[0087]
The surface light source 16 may be used as an auxiliary light source during reflective display using external light, and the surface light source 16 emits illumination light during reflective display, thereby increasing the brightness of the reflective display. Can be raised.
[0088]
In the above embodiment, the reflection means 14 has a configuration in which the reflection film 15 is provided on the rear surface of the light guide plate 17 of the surface light source 16, but the reflection means has a surface light source on the rear side of the semi-transmissive reflection film. It is good also as a structure which arranged.
[0089]
Further, the liquid crystal display device of the above embodiment performs both a reflective display using external light and a transmissive display using illumination light from the surface light source 16. The present invention can be applied to a liquid crystal display device that performs only reflective display using the method described above, and in that case, the reflective means may be only a reflective film.
[0090]
Further, in the above embodiment, the diffusion layer 13 is disposed between the liquid crystal cell 1 and the rear polarizing plate 12, but the diffusion layer 13 may be provided between the liquid crystal cell 1 and the reflection means 14. It may be disposed on the rear side of the rear polarizing plate 12, and a part of the reflected light of the light incident from an oblique direction with respect to the normal line of the screen is directed to the front direction which is the display observation direction. The reflecting means for allowing the light to enter the cell may be provided in the reflecting means, for example, by making the reflecting film 15 of the reflecting means 14 a diffuse reflecting film.
[0091]
Further, in the above embodiment, the front polarizing plate 10 is arranged with its absorption axis 12a substantially parallel to the liquid crystal molecule orientation direction 2a near the front substrate 2 of the liquid crystal cell 1. Reference numeral 10 may be arranged such that its transmission axis is substantially parallel to the liquid crystal molecule alignment direction 2a in the vicinity of the front substrate 2 of the liquid crystal cell 1.
[0092]
Further, the liquid crystal display device of the above embodiment displays a black and white image, but the liquid crystal cell 1 is provided with a plurality of color filters, for example, three color filters of red, green and blue, corresponding to a plurality of pixels, respectively. The liquid crystal cell 1 may be provided to display a color image. Further, the liquid crystal cell 1 is not limited to the active matrix type, and may be a simple active matrix type liquid crystal cell.
[0093]
【The invention's effect】
In the liquid crystal display device of the present invention, a liquid crystal cell in which liquid crystal molecules of a liquid crystal layer are substantially twist-aligned at a twist angle of 90 ° is provided with a front polarizer and one of an absorption axis and a transmission axis of the liquid crystal cell. The liquid crystal molecules are arranged substantially parallel to the liquid crystal molecule alignment direction in the vicinity of the front substrate of the cell, and the rear polarizing plate is disposed on the rear side of the liquid crystal cell with its absorption axis substantially in relation to the absorption axis of the front polarizing plate. The liquid crystal cell and the front polarizer, between the liquid crystal cell and the front polarizing plate, optically has a biaxial film, the x-axis having the largest refractive index on a plane parallel to the film surface And a biaxial retardation plate having a z-axis having the smallest refractive index in a direction perpendicular to each of these axes, the x-axis being substantially the absorption axis of the front polarizing plate. Are arranged in parallel with each other, and Δ The value of nd is 380-420 nm, and the refractive index n in the x-axis direction of the biaxial retardation plate _x And the refractive index n in the y-axis direction _y Is 200 to 350 nm, and Nz = (n _x -N _z ) / (N _x -N _y ), The shadow of the electric field applied pixel is generated in the bright display portion corresponding to the non-electric field pixel adjacent to the electric field applied pixel of the liquid crystal cell. And a good quality image without double images can be displayed.
[0094]
In the liquid crystal display device of the present invention, it is preferable that a light diffusing unit is provided between the liquid crystal cell and the reflecting unit or in the reflecting unit. A part of the reflected light of the light can be incident on the liquid crystal cell in a front direction which is a display observation direction.
[0095]
Further, in this liquid crystal display device, it is preferable that the reflection unit includes a surface light source that emits illumination light on the front side, and by doing so, a reflection display using external light, And the transmissive display using the illumination light.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a part of the liquid crystal display device, in which hatching is omitted.
FIG. 3 is a cross-sectional view of a liquid crystal display device of a comparative example in which a biaxial retardation plate is omitted from the liquid crystal display device of the example, in which a part of hatching is omitted.
FIG. 4 is a diagram showing the relationship between the incident angle of light and the transmittance of a black display portion corresponding to an electric field application pixel in the liquid crystal display devices of the example and the comparative example.
FIG. 5 is a diagram showing the relationship between the incident angle of light and the chromaticity of white display of the liquid crystal display devices of the example and the comparative example.
[Explanation of symbols]
1: Liquid crystal cell
2,3 ... substrate
5,6 ... electrode
9 ... Liquid crystal layer
9a: Liquid crystal molecules
A _(OFF) … Field-free pixels
A _(ON) ... Electric field application pixels
10 Front polarizing plate
10a ... absorption axis
11 ... biaxial retardation plate
11x ... x axis
12: Rear polarizing plate
12a: absorption axis
13 ... Diffusion layer
14 ... Reflecting means
15 ... Reflection film
16 ... Surface light source

Claims

Electrodes for forming a plurality of pixels are provided on the opposing inner surfaces of the front substrate, which is the display observation side, and the rear substrate, which opposes the front substrate, by opposing regions. A liquid crystal cell provided with a liquid crystal layer in which liquid crystal molecules are substantially twisted at a twist angle of 90 °,
A front polarizer disposed on the front side of the liquid crystal cell,
A retardation element disposed between the liquid crystal cell and the front polarizer,
A rear polarizer disposed on the rear side of the liquid crystal cell,
Reflecting means disposed on the rear side of the rear polarizing plate and reflecting light incident from the front side,
The front polarizing plate is disposed so that one of the absorption axis and the transmission axis thereof is substantially parallel to the liquid crystal molecule alignment direction near the front substrate of the liquid crystal cell, and the rear polarizing plate has the absorption axis. Is arranged substantially orthogonal to the absorption axis of the front polarizing plate,
The value of the product Δnd of the refractive index anisotropy Δn of the liquid crystal of the liquid crystal cell and the thickness of the liquid crystal layer is set to 380 to 420 nm,
The retardation element is made of an optically biaxial film, and on a plane parallel to the film surface, the x-axis having the largest refractive index and the y-axis orthogonal to it are orthogonal to these axes, respectively. direction, had the most refractive index lower z-axis, the x-axis direction of the refractive index n _x, the refractive index in the y-axis direction n _y, and the refractive index of the z-axis direction is n _z, the difference between the refractive indices _{n x} and the refractive index _{n y} in the y-axis direction of the x-axis direction _{_{200~350nm, Nz = (n x -n}} z) / Nz represented by the formula _(n x -n _y) The biaxial retardation plate has a coefficient of 1.5 or more, and the biaxial retardation plate is disposed with the x-axis substantially parallel to the absorption axis of the front polarizing plate. A liquid crystal display device characterized by the above-mentioned.

2. The liquid crystal display device according to claim 1, wherein the biaxial retardation plate is made of a biaxially stretched polycarbonate film.

2. The liquid crystal display device according to claim 1, wherein a light diffusing unit is provided between the liquid crystal cell and the reflecting unit or in the reflecting unit.

2. The liquid crystal display device according to claim 1, wherein the reflection unit includes a surface light source that emits illumination light on a front side.