JP2004252082A - Liquid crystal display device - Google Patents

Liquid crystal display device Download PDF

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Publication number
JP2004252082A
JP2004252082A JP2003041501A JP2003041501A JP2004252082A JP 2004252082 A JP2004252082 A JP 2004252082A JP 2003041501 A JP2003041501 A JP 2003041501A JP 2003041501 A JP2003041501 A JP 2003041501A JP 2004252082 A JP2004252082 A JP 2004252082A
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Prior art keywords
liquid crystal
crystal display
light guide
plate
light
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JP2003041501A
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Japanese (ja)
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JP4327473B2 (en
JP2004252082A5 (en
Inventor
Teruo Ebihara
照夫 海老原
Mitsuru Suginoya
充 杉野谷
Shigeru Senbonmatsu
茂 千本松
Masahiko Tomikawa
昌彦 富川
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Seiko Instruments Inc
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Seiko Instruments Inc
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Priority to JP2003041501A priority Critical patent/JP4327473B2/en
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Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the occurrence of uneven luminance and color irregularity caused by retroreflective light from a reflective polarizer due to residual birefringence of a light guide plate in a liquid crystal display device. <P>SOLUTION: A liquid crystal display part consisting of a liquid crystal display panel with an upper polarizing plate and a lower polarizing plate disposed thereon, the reflective polarizer with a transmission axis placed in the same direction as that of the lower polarizing plate disposed on the lower side of the liquid crystal display part and a backlight consisting of the light guide plate, a light source and a specular reflection plate disposed on the lower side of the reflective polarizer are arranged. An optical retardation plate with 850 nm or higher retardation value is arranged between the reflective polarizer and the specular reflection plate. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【0001】
【発明の属する技術分野】
本発明は、液晶表示装置、特に反射偏光子と鏡面反射板を有する導光板を使用する液晶表示装置に関する。
【0002】
【従来の技術】
従来の液晶表示装置には、液晶パネルの背面に半透過反射板およびバックライトを配置し、周囲が明るくても暗くても使用できる半透過型の液晶液晶表示装置がある。また、液晶パネルとバックライトの間に反射偏光子を配置した構成が知られている(例えば、特許文献1参照。)。
【0003】
【特許文献1】
特表平9−506984号公報(第6〜7頁、第1図、第2図)
【0004】
【発明が解決しようとする課題】
しかし、液晶パネルとバックライトの間に反射偏光子を配置した構成を、半透過型液晶装置として使用した場合には、以下のような欠点がある。特許文献1で開示されたように、光学キャビティ24の裏側にバックライトを配置した半透過型液晶装置では、外光を利用する反射型とバックライトの光を利用する透過型で表示のネガ・ポジが反転してしまう。よって、薄暗い環境で、外光とバックライトを同時に使用すると、コントラストが低下してしまう欠点を有する。
【0005】
また、特許文献1には、背面偏光子23の透過軸と反射偏光子の透過軸が同一方向に設定された半透過型液晶装置が開示されている。しかし、このような構成の半透過型表示装置を反射で使用した場合には、拡散反射層39により偏光が解消してしまうため暗くなる。更に、拡散反射層39の拡散があらゆる方向に拡散するので反射光の密度が低下して更に暗くなる。
【0006】
更に、上述した拡散反射層に関わる欠点を解消するために、拡散反射層の替わりに鏡面反射板を用いると、新たにバックライトの輝度ムラ、色ムラが発生することになる。図2を用いてそのムラの発生原因を説明する。図示するように、上偏光板1と液晶パネル2と下偏光板3は一体となり液晶表示部10を構成し、その下に反射偏光子4が配置されている。反射偏光子4と下偏光板3の透過軸方向は同一方向になるように配置されている。更にその下に、光源8と導光板6と鏡面反射板7で構成されるバックライトを配置している。導光板6の右半分の×印部は複屈折の大きい領域を模式的に表現している。また、左半分の無印部は複屈折の小さい部分を表現している。×印部の複屈折をΔnd1と表現し、無印部の複屈折をΔnd2で表現する。
【0007】
無印部においての再帰反射光の一部を以下に示す。バックライトの照射光ab(図中矢印で記載、以下同様)は反射偏光子4で透過直線偏光aと反射直線偏光bに分離される。反射直線偏光bは、導光板6を透過し鏡面反射板7で再度反射され導光板6を通過して反射偏光子4へ到達する。反射偏光子へ到達した反射直線偏光b1は導光板6を2回透過するため2・Δnd1の位相差を持った楕円偏光に変換されている。楕円偏光b1の一部は反射偏光子4を透過して直線偏光a1となり、これが再帰反射光となる。この再帰反射光a1は2・Δnd1の位相差に対応した干渉色を呈する。
【0008】
同様の作用で、×印部での再帰反射光A1は2・Δnd2の位相差に対応した干渉色を呈することになる。すなわち、液晶表示部10を透過する光は、×印部でa+a1、無印部でA+A1となり、色むらとなる。また、導光板の複屈折が小さい時には干渉色は白色となる。この場合、導光板の面内複屈折ムラは輝度ムラとなる。
【0009】
導光板面内に複屈折ムラが無い場合には、上記の色ムラ、輝度ムラは発生しない。導光板の複屈折ムラの発生原因はその製造方法にある。図3は導光板を上から見た複屈折ムラを説明する模式図である。図中矢印は複屈折の発生部を示す。また、矢印の方向は複屈折の光学軸方向を示す。導光板を樹脂成形にて製作する場合のゲート部位置を模式的に示した。複屈折の発生部は成形時のゲート部9の位置近くに発生し樹脂の流入方向に発生している。図4はゲート部をコーナーに配置した時の導光板の複屈折分布を模式的に示したものである。
【0010】
上記の複屈折ムラは成形条件で低減可能である。しかし、実用的な成形条件での残留する複屈折は0.8mm程度の厚みの導光板で位相差値100nm程度である。位相差値を更に低減するには製造のコストアップを招き実用的でない。
【0011】
本発明の目的は、背面偏光子の透過軸と反射偏光子の透過軸を同一方向に設定され、導光板の下に鏡面反射板を設けた構成の半透過型液晶装置に生ずる、導光板の残留複屈折による輝度ムラ、色ムラを改善することになる。
【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、本発明の液晶表示装置は、液晶表示パネルと、液晶表示パネルの背後に設けられ、液晶表示パネルに照明光を導光する導光体と、液晶表示パネルと導光体の間に設けられた下偏光板と、導光板の背後に設けられた鏡面反射板と、下偏光板と導光体の間に設けられ、下偏光板の透過軸と同一方向の透過軸を有する反射偏光子と、反射偏光子と鏡面反射板の間に設けられた位相差板と、を備える構成とした。さらに、位相差板の位相差値を850nm以上に設定した。このように、位相差板の位相差値を850nm以上に設定しているのは、導光板の残留複屈折に伴う面内の位相差値のムラが100nm程度の場合に設定した値である。100nmより大きくなる場合は、位相差板の位相差値をより大きな値に設定することでより大きい効果が得られる。
【0013】
また、位相差板の光学軸を、反射偏光子の透過軸に対して45°方向に配置することにより、最もムラ解消の効果を発揮する。45°からずれるとサインの二乗に比例して効果が低減する。
【0014】
あるいは、液晶表示パネルの背後に設けられ、液晶表示パネルに照明光を導光する導光体と、液晶表示パネルと導光体の間に設けられた下偏光板と、導光板の背後に設けられた鏡面反射板と、下偏光板と導光体の間に設けられ、下偏光板の透過軸と同一方向の透過軸を有する反射偏光子と、反射偏光子と鏡面反射板の間に、導光板を上から見た面内の位相差値の最大値と最小値の間の位相差値を持つ位相差板を設け、導光板の光学軸と位相差板の光学軸が直交するように配置する構成により、輝度ムラ、色ムラを改善している。
【0015】
あるいは、液晶表示パネルの背後に設けられ、液晶表示パネルに照明光を導光する導光体と、液晶表示パネルと導光体の間に設けられた下偏光板と、導光板の背後に設けられた鏡面反射板と、下偏光板と導光体の間に設けられ、下偏光板の透過軸と同一方向の透過軸を有する反射偏光子と、反射偏光子と鏡面反射板の間に、多数のドメインからなり、各ドメイン間の配向方向がランダムな高分子液晶フィルムを備える構成により、輝度ムラ、色ムラを改善している。
【0016】
あるいは、液晶表示パネルの背後に設けられ、液晶表示パネルに照明光を導光する導光体と、液晶表示パネルと導光体の間に設けられた下偏光板と、導光板の背後に設けられた鏡面反射板と、下偏光板と導光体の間に設けられ、下偏光板の透過軸と同一方向の透過軸を有する反射偏光子を備えるとともに、反射偏光子の透過軸方向が導光板の樹脂成形ゲート方向と同一方向になるように設定した。
【0017】
【発明の実施の形態】
本発明による液晶表示装置は、液晶表示パネルに照明光を導光する導光体と、液晶表示パネルと導光体の間に設けられた下偏光板と、導光板の背後に設けられた鏡面反射板と、下偏光板と導光体の間に設けられ、下偏光板の透過軸と同一方向の透過軸を有する反射偏光子と、反射偏光子と鏡面反射板の間に設けられた位相差板を備えている。さらに、位相差板の位相差値を850nm以上にした。
【0018】
このように、反射偏光子と鏡面反射板の間に、位相差値850nm以上の位相差板を設けた構成の液晶表示装置を外光により観察すると、液晶表示部で画像情報が変調され、反射偏光子、位相差板、導光板を透過して、鏡面反射板で反射され、光路と逆向きに進行し、液晶表示部を再度透過して画像表示を可能とし、反射型として使用可能である。
【0019】
透過モードでバックライトを点灯して使用すると、反射偏光子を透過したバックライトの光が液晶表示部を透過して画像表示を可能とし、透過型として使用可能としている。更に、反射偏光子へ入射するバックライト光の一部を反射偏光子の反射光として反射させ、位相差板、導光板を透過し、鏡面反射板で反射され、前記光路と逆向きに進行し、液晶表示部を再度透過して再帰光として液晶表示部を透過して画像表示を可能とし、表示輝度の上昇を可能としている。
【0020】
上記構成によるメリットは外光とバックライトを同時に利用しても、外光の反射光とバックライトの透過光が協力的に作用して、単独で表示するより、明るくなる、いわゆる半透過型としての使用できる。さらに、反射偏光子と鏡面反射板の間に配置する位相差板の位相差値を850nm以上とすることで輝度ムラ、色ムラのない表示を実現していることにある。
【0021】
以下に上記効果が得られる位相差板の作用について、図5の本発明の作用を説明する概略図を使用して説明する。導光板6の右半分の×印部は複屈折の大きい領域を模式的に表現している。また、左半分の無印部は複屈折の小さい部分を表現している。×印部の複屈折をΔnd1と表現し、無印部の複屈折をΔnd2で表現する。また、位相差板の位相差値をΔndfと表現する。
【0022】
無印部においての再帰反射光の一部を以下に示す。バックライトの照射光ab(図中矢印で記載、以下同様)は反射偏光子4で透過直線偏光aと反射直線偏光bに分離される。反射偏光子4で反射された反射直線偏光bは、位相差板5と導光板6を透過し鏡面反射板7に到達する。到達した光はさらにこの鏡面反射板7で反射され、再度、導光板6と位相差板5を透過して反射偏光子4に到達する。ここで、反射偏光子4に再度到達した反射光(偏光状態)は、位相差板5と導光板6を2回透過するため、2・Δndfと2・Δnd1の位相差値の和を持った楕円偏光b1に変換されている。楕円偏光b1の一部は反射偏光子4を透過して直線偏光a1となり、これが再帰反射光となる。この再帰反射光a1は2・Δndfと2・Δnd1の位相差値の和に対応した干渉色を呈する。同様の作用で、×印部での再帰反射光A1は2・Δndfと2・Δnd2の位相差の和に対応した干渉色を呈することになる。液晶表示部10を透過する光は、×印部でa+a1、無印部でA+A1となり、a+a1とA+A1との差が輝度ムラ、色むらとなる。
【0023】
ここで、本発明では位相差板5のΔndfを850nm以上に設定している。この値は、一般の導光板に存在する残留複屈折の位相差値より充分大きな値になっている。一般に、位相差値が大きなるにつれて、干渉色は白色になる。図9は図5の構成での干渉色のシミュレーション結果である。光源に白色LEDを使用し、導光板の複屈折を無いと仮定し、位相差板の位相差値に対する反射偏光子を出射する光の色度x、yの関係を示す。ここで使用する色度はCIE1931表色系に従う。位相差板の位相差値が850nmより小さいと色度xyのバラツキが大きくなっている。850nm以上ではバラツキが小さくなり、xyとも0.325〜0.330の値に収束する。この値は白色を示す値である。
【0024】
以上、位相差板5の位相差値を850nm以上に設定しておけば導光板6に残留複屈折が存在するため、導光板6面内で位相差値がばらついても、位相差板5の位相差値と導光板の位相差値が足し算されて、トータルの位相差値が大きくなるので輝度ムラ色ムラを無くす事が可能となる。
【0025】
上記の構成は、位相差板の光学軸と導光板の光学軸が同一方向で位相差値が足し算されることで最も効果を発揮する。しかし、仮に位相差板の光学軸と導光板光学軸が直交していても、導光板の位相差値が100nm以下であれば位相差板を用いない場合に比較して良い結果が得られる。
【0026】
また、図5では、位相差板5は反射偏光子4と導光板6の間に設けられているが、導光板6と鏡面反射板7の間に設けても基本的に上述と同様の効果が得られる。
【0027】
次に、上記の効果は以下の構成でも容易に実現できる。液晶表示パネルに照明光を導光する導光体と、液晶表示パネルと導光体の間に設けられた下偏光板と、導光板の背後に設けられた鏡面反射板と、下偏光板と導光体の間に設けられ、下偏光板の透過軸と同一方向の透過軸を有する反射偏光子と、反射偏光子と鏡面反射板の間に、導光板を上から見た面内の位相差値の最大値と最小値の間、望ましくは中間の位相差値を持つ位相差板を導光板の光学軸と位相差板の光学軸が直交するように配置することで、輝度ムラ、色ムラを改善している。
【0028】
以下に上記効果が得られる位相差板の作用について、図10の本発明の作用を説明する概略図を使用して説明する。図中、導光板6は90°立てた状態で、×印部は複屈折の大きい領域を模式的に表現している。また、無印部は複屈折の小さい部分を表現している。ここで、計算を簡略化するために、×印部の複屈折を位相差値100nmとし、無印部の位相差値を50nmとし、図中に記載した。このとき、位相差板の位相差値は望ましくは100nmと50nmの中間の位相差値であり、75nmとなる。
【0029】
また、図中の楕円の長軸方向は複屈折の光学軸方向を表現する。従って位相差板の光学軸は導光板の光学軸と直交して配置されることが望ましい。×印部は屈折の大きい領域は導光板の位相差値と位相差板の位相差値が減算され25nmの位相差値が合成される。同様に、無印部では、×印と直交して光学軸で25nmの位相差値が合成される。ここで、図9のシミュレーション結果を参照すると、位相差値25nmでの干渉色はほとんど白色を示す。その結果、輝度ムラ色むら発生を改善可能としている。
【0030】
次に、上記の効果は以下の構成でも容易に実現できる。液晶表示パネルに照明光を導光する導光体と、液晶表示パネルと導光体の間に設けられた下偏光板と、導光板の背後に設けられた鏡面反射板と、下偏光板と導光体の間に設けられ、下偏光板の透過軸と同一方向の透過軸を有する反射偏光子と、反射偏光子と鏡面反射板の間に設けられるとともに、多数のドメインからなり、各ドメイン間の配向方向がランダムな高分子液晶フィルムを備えることにより、液晶表示装置の輝度ムラ、色ムラを改善可能としている。
【0031】
以下に上記効果が得られる高分子液晶フィルムの作用について、図7の本発明高分子液晶フィルムの構造を示す模式図を使用して、その作用を説明する。図中のハッチングで分割された領域は、液晶分子の配向方向の違うドメイン10を表している。ドメインのサイズは液晶パネルの画素よりも小さくし、配向方向に複屈折の光学軸方向がある。この高分子液晶フィルムのランダムな光学軸を持った位相差値が導光板の複屈折の位相差値と合成される。結果、導光板の位相差値がランダムな光学軸により足し算と減算が面内でランダムを行われるので、結果として導光板の複屈折ムラは平準化される。
【0032】
高分子液晶フィルムのドメインサイズは液晶パネルの画素より小さく、高分子液晶フィルムの液晶パネルの画素との間隔は、液晶パネルの基板、偏光板などの厚みで離れているので、ドメインサイズによる表示画質の低下は低減され、導光板の複屈折ムラによる輝度ムラ、色ムラの改善された表示が得られる事になる。
【0033】
次に、上記の効果は以下の構成でも容易に実現できる。少なくとも、液晶表示パネルに上偏光板と下偏光板を配置した液晶表示部と、その下側に下偏光板の透過軸と同一方向に透過軸を配置した反射偏光子と、さらにその下側に導光板と光源と鏡面反射板からなるバックライトを配置し、前記導光板の樹脂成形ゲート方向を前記反射偏光子の透過軸方向と同一方向になるように配置する事で、輝度ムラ、色ムラを改善している。
【0034】
以下に上記効果が得られる作用について、図8の本発明の構成模式図を使用して、説明する。上偏光板1と液晶パネル2と下偏光板3は一体となり液晶表示部を構成し、その下に反射偏光子4が配置されている。反射偏光子4と下偏光板3の透過軸方向は同一方向になるように配置されている。更にその下に、導光板6と鏡面反射板7とで構成されるバックライトを配置している。図中バックライトの光源は省略した。導光板6の樹脂成形ゲート方向9と反射偏光子4の透過軸方向が同一方向になるように配置されているので、導光板の光学軸方向と反射偏光子の透過軸方向が一致している。
【0035】
このような構成の液晶表示装置は、従来技術の構成と比較して、異なる点は導光板の光学軸方向と反射偏光子の透過軸方向が一致している事である。この構成は、反射偏光子の反射軸と鏡面反射板と反射偏光子の透過軸とで構成される偏光光学系において、等価的にクロスニコルの配置の中に、導光板の光学軸方向を偏光軸方向に配置したのと同じになる。この配置では、導光板の複屈折による位相差値の影響を受けないため、輝度ムラ、色ムラが発生しない事となる。
【0036】
【実施例】
以下、図面を参照して本発明にかかる液晶表示装置の実施例を説明する。
(実施例1)
図1は、本実施例における液晶表示装置の断面構造を示す模式図である。図6は図1の断面構図の各要(光源を除く)における偏光に関わる透過軸と光学軸を矢印で表したものである。図1に示すように、上偏光板1と液晶パネル2と下偏光板3は一体となり液晶表示部10を構成している。液晶パネルはTN型に代表される透過モードを使用できる。本構成ではバックライトの導光板6の背面側に反射板として使用する鏡面反射板7が配置されており、これにより反射モードを表示する。反射板で鏡面反射するために、上偏光板1と鏡面反射板7の間のどこかに拡散層を設ける必要がある。液晶パネル2と偏光板を貼り合わせる透明粘着剤に拡散層の機能を持たせても良く、あるいは、位相差板に拡散層の機能を持たせても良い。また、拡散層に散乱フィルムを用い、上偏光板1と鏡面反射板7の間のどこかに配置してもよい。拡散層は反射モードで反射光を拡散する機能と透過モードでバックライトの光を拡散する機能の両方を併せ持っていてもよい。また、拡散層は従来技術のように偏光を解消するような完全拡散をする必要は無く、外光を効率良く観測者方向に集光し、鏡面反射板を介して反射するような拡散角度に異方性を持たせた拡散層を使用することができる。
【0037】
反射偏光子としては、住友スリーエム株式会社のDBEF(Dual−Brightness−Enhancement−Film)を使用し液晶表示部10と一体化しても良い。ただし、反射偏光子の透過軸と下偏光板の透過軸は同一方向になるように配置されている。反射偏光子はバックライトの光を再帰反射することで液晶表示部10の透過の輝度を高くする機能があれば良く、円偏光の選択反射を利用した反射フィルムを使用しても良い。
【0038】
位相差板5には、ポリカーボネートやポリエステル等のポリマーを延伸することにより製造された、光学軸がフィルム面に平行にある一軸延伸フィルムを使用した。位相差値は850nmのフィルムを反射偏光子の透過軸と45°の角度で配置した。
【0039】
バックライトに使用する光源8は白色LEDを光源として使用している。導光板6にはアクリルを射出成形し、導光面の片側にプリズムを形成している。このプリズムは導光板内部を導光する光を液晶表示部10の方向に反射する機能を有している。導光板にはプリズムや溝、ホログラムなど光を反射する方式は使用することができる。しかし、プリズムのかわりに反射ドットなどの偏光を解消する拡散反射方式は使用できない。反射ドット方式としてはチタン白などの白色塗料を印刷した方式である。
【0040】
導光板の残留複屈折はクロスニコルの偏光板の間に、導光板を入れて観察出来る。ゲート部から樹脂の流入方向にしたがって段段と小さくなっている。位相差値を偏光顕微鏡で測定すると、ゲート近くで80nmあり、ゲートの反対側で10nmであった。この複屈折の分布はゲートから遠ざかるに従って連続的に減少している。
【0041】
鏡面反射板7としては、ポリエステルフィルム表面に銀をコーティングした表面反射鏡を使用した。表面反射鏡として使用することでポリエステルフィルムを複屈折の影響を排除している。また、逆に前記表面鏡を裏返して使用して、フィルムの複屈折を積極的に利用しても良い。その場合はフィルムの複屈折による位相差値を850nm以上にする必要がある。これにより、位相差板5を省略出来薄型化を可能とする。
【0042】
本発明では、上記に説明した鏡面反射板を反射板として使用して、反射モードで外光を効率良く反射する構成にしているにも関わらず、透過モードでバックライトの光を反射偏光子で再帰反射光として使用するときに生ずるバックライトの複屈折ムラに起因する輝度ムラ、色ムラを、位相差板の位相差値を850nm以上に設定することで、その発生を解消している。
(実施例2)
本実施例の液晶表示装置は、実施例1の構成で位相差板の位相差値を導光板の位相差値の最大値と最小値の間、望ましくは中間の位相差値を持つ位相差板に置き換えた構成である。この構成では、導光板の光学軸と位相差板の光学軸が直交するように配置することで最も効果が得られる。直交からずれても、効果の低下は、ずれた角度のサインの二乗で変化するので多少の角度ずれは影響無い。
【0043】
導光板の複屈折ムラは偏光顕微鏡で測定可能である。また、導光板の成形条件が安定していればムラも安定しているので、実用的に位相差板の位相差値と角度を決定できる。導光板の光学軸方向にムラがある場合は、最も光学軸方向の優勢な方向を基準に位相差板の光学軸を直交配置するのが望ましい。位相差板としては一軸延伸フィルム以外にも、一軸配向高分子液晶フィルムを使用できる。
【0044】
本発明では、位相差板以外を実施例1の構成と同様にしても、鏡面反射板を反射板として使用し、反射モードで外光を効率良く反射する構成にしているにも関わらず、透過モードでバックライトの光を反射偏光子で再帰反射光として使用する時に生ずるバックライトの複屈折ムラに起因する輝度ムラ、色ムラを、位相差板の位相差値を導光板の位相差値の最大値と最小値の間、望ましくは中間の位相差値を持つ位相差板に置き換えた構成とする事で、その発生を解消している。
【0045】
(実施例3)
本実施例の液晶表示装置は、実施例1の位相差板のかわりに、多数のドメインからなり、各ドメイン間の配向方向がランダムな高分子液晶フィルムを配置した構成である。この構成では、導光板の光学軸と関係無く高分子液晶フィルムを配置することができる。高分子液晶フィルムは、光反応性高分子液晶フィルムの軸選択的光反応による光−熱誘起配向を利用して製作される。光反応性高分子液晶材料を溶媒で溶解し、スピンコート法により石英基板に塗布し、超高圧水銀灯を用いて直線偏光紫外光をいろいろな角度からドメインサイズで照射する。ドメインサイズは紫外光用のマスクにより面内に多数個配置され、角度をランダムに選択露光されても良い。露光後、熱処理により固化して保護フィルムでカバーし製作した。
【0046】
本発明で使用される高分子液晶フィルムの製法は上記の方法に限定されるものでなく、ドメインの光学軸がランダムであれば良い。また、各ドメイン間の位相差値は必ずしも一定である必要はない。位相差値がドメイン間でランダムであっても良い。また、高分子液晶フィルムの配置も、反射偏光子と鏡面反射板の間にあれば良く、導光板あるいは鏡面反射板のミラー面の上で一体化されてもよい。
【0047】
本発明では、位相差板以外を実施例1の構成と同様にしても、鏡面反射板を反射板として使用し、反射モードで外光を効率良く反射する構成にしているにも関わらず、透過モードでバックライトの光を反射偏光子で再帰反射光として使用する時に生ずるバックライトの複屈折ムラに起因する輝度ムラ、色ムラを、多数のドメインからなり、各ドメイン間の配向方向がランダムな高分子液晶フィルムに置き換えへ、反射偏光子と鏡面反射板の間に、前記高分子液晶フィルムを配置した構成とする事で、その発生を解消している。
【0048】
(実施例4)
実施例1の構成で、位相差板を取り除き、導光板の樹脂成形ゲート方向を反射偏光子の透過軸方向と同一方向になるように配置した構成の液晶表示装置について説明する。
【0049】
本発明では、導光板のゲート部から樹脂流入時の流れ方向に発生する複屈折率分布を予め測定し導光板の残留複屈折の光学軸を見極めて、反射偏光子の透過軸と同じ方向となるようにするのが望ましい。ただし、液晶表示部の上偏光板の透過軸は12時−6時視角方向から45°傾けるのが一般的である。これは、偏光サングラスを掛けたときの視界を確保するためである。このため、液晶表示部に90°ツイストTN液晶を使用すると、反射偏光子の透過軸も視角方向から45°傾くことになる。したがって、導光板のゲート方向も視角方向から45゜傾ける。
【0050】
また、反射偏光子の透過軸に導光板の光学軸を同じ方向になるように配置したが、反射偏光子の反射軸に導光板の光学軸を合わせても同様に輝度ムラ、色ムラを改善できる。
【0051】
本発明では、実施例1の構成から位相差板を取り除き、導光板の樹脂成形ゲート方向を反射偏光子の透過軸方向と同一方向になるように配置し、鏡面反射板を反射板として使用し、反射モードで外光を効率良く反射する構成にしているにも関わらず、バックライトの複屈折ムラに起因する輝度ムラ、色ムラを、の発生を解消している。
【0052】
【発明の効果】
以上説明したように、本発明の液晶表示装置によれば、鏡面反射板を反射板として使用して、反射モードで外光を効率良く反射する構成にしているにも関わらず、透過モードでバックライトの光を反射偏光子で再帰反射光として使用するときに生ずるバックライトの複屈折ムラに起因する輝度ムラ、色ムラを解消し、屋外の外光が明るい場所、室内の照明下、外光のない暗い場所いずれにても、明るく均一性の良い表示を容易に実現できる。そのため、民生品市場で液晶表示装置が多用されているパソコン、カメラ、携帯電話、時計をはじめとする電子機器分野で商品価値を高めることができる。
【図面の簡単な説明】
【図1】本発明の表示装置の断面構造を示す模式図である。
【図2】従来の技術におけるムラ発生原因説明図である。
【図3】導光板を上から見た複屈折ムラを説明する模式図である。
【図4】ゲート部をコーナーに配置した時の導光板の複屈折分布を示す模式図である。
【図5】本発明の作用を説明する概略図を示した図である。
【図6】偏光に関わる透過軸と光学軸を矢印で表した図である。
【図7】本発明高分子液晶フィルムの構造を示す模式図である。
【図8】本発明の構成模式図である。
【図9】干渉色のシミュレーション結果を表した図である。
【図10】本発明の作用を説明する概略図である。
【符号の説明】
1 上偏光板
2 液晶パネル
3 下偏光板
4 反射偏光子
5 位相差板
6 導光板
7 鏡面反射板
8 光源
9 ゲート部
[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device using a light guide plate having a reflective polarizer and a specular reflector.
[0002]
[Prior art]
2. Description of the Related Art As a conventional liquid crystal display device, there is a transflective liquid crystal display device in which a transflective plate and a backlight are arranged on the back of a liquid crystal panel and can be used regardless of whether the surroundings are bright or dark. Further, a configuration in which a reflective polarizer is arranged between a liquid crystal panel and a backlight is known (for example, see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 9-509684 (pages 6 and 7, FIG. 1 and FIG. 2)
[0004]
[Problems to be solved by the invention]
However, when a configuration in which a reflective polarizer is disposed between a liquid crystal panel and a backlight is used as a transflective liquid crystal device, there are the following disadvantages. As disclosed in Patent Document 1, in a transflective liquid crystal device in which a backlight is disposed on the back side of an optical cavity 24, a negative type of display is used as a reflective type using external light and a transmissive type using backlight light. Positive is reversed. Therefore, there is a disadvantage that the contrast is reduced when external light and a backlight are used simultaneously in a dim environment.
[0005]
Patent Document 1 discloses a transflective liquid crystal device in which the transmission axis of the back polarizer 23 and the transmission axis of the reflective polarizer are set in the same direction. However, when the transflective display device having such a configuration is used for reflection, the light is darkened because the polarized light is eliminated by the diffuse reflection layer 39. Further, since the diffusion of the diffuse reflection layer 39 is diffused in all directions, the density of the reflected light is reduced and the light is further darkened.
[0006]
Further, if a specular reflector is used in place of the diffuse reflection layer in order to solve the above-mentioned drawbacks related to the diffuse reflection layer, luminance unevenness and color unevenness of the backlight will newly occur. The cause of the unevenness will be described with reference to FIG. As shown in the drawing, the upper polarizer 1, the liquid crystal panel 2, and the lower polarizer 3 are integrated to form a liquid crystal display unit 10, and a reflective polarizer 4 is disposed below the liquid crystal display unit 10. The transmission axes of the reflective polarizer 4 and the lower polarizer 3 are arranged in the same direction. Further, a backlight composed of a light source 8, a light guide plate 6, and a specular reflection plate 7 is arranged therebelow. The mark x in the right half of the light guide plate 6 schematically represents a region having a large birefringence. Further, the unmarked portion in the left half represents a portion having a small birefringence. The birefringence of the mark x is represented by Δnd1, and the birefringence of the unmarked part is represented by Δnd2.
[0007]
Part of the retroreflected light at the unmarked portions is shown below. The irradiation light ab of the backlight (indicated by an arrow in the figure, the same applies hereinafter) is separated by the reflective polarizer 4 into transmitted linearly polarized light a and reflected linearly polarized light b. The reflected linearly polarized light b passes through the light guide plate 6, is reflected again by the specular reflection plate 7, passes through the light guide plate 6, and reaches the reflective polarizer 4. The reflected linearly polarized light b1 that has reached the reflective polarizer passes through the light guide plate 6 twice, and is converted into elliptically polarized light having a phase difference of 2 · Δnd1. Part of the elliptically polarized light b1 passes through the reflective polarizer 4 and becomes linearly polarized light a1, which is retroreflected light. This retroreflected light a1 exhibits an interference color corresponding to a phase difference of 2 · Δnd1.
[0008]
By the same operation, the retroreflected light A1 at the cross mark portion exhibits an interference color corresponding to the phase difference of 2 · Δnd2. That is, the light transmitted through the liquid crystal display unit 10 is a + a1 at the x mark part and A + A1 at the non-mark part, resulting in color unevenness. When the birefringence of the light guide plate is small, the interference color is white. In this case, the in-plane birefringence unevenness of the light guide plate becomes a brightness unevenness.
[0009]
When there is no birefringence unevenness in the light guide plate surface, the above-described color unevenness and luminance unevenness do not occur. The cause of the birefringence unevenness of the light guide plate lies in its manufacturing method. FIG. 3 is a schematic diagram illustrating birefringence unevenness when the light guide plate is viewed from above. Arrows in the figure indicate portions where birefringence occurs. The direction of the arrow indicates the direction of the birefringent optical axis. The position of the gate portion when the light guide plate is manufactured by resin molding is schematically shown. The portion where the birefringence occurs is generated near the position of the gate portion 9 during molding and is generated in the resin inflow direction. FIG. 4 schematically shows the birefringence distribution of the light guide plate when the gate is arranged at the corner.
[0010]
The above birefringence unevenness can be reduced by molding conditions. However, the residual birefringence under practical molding conditions is about 100 nm for a light guide plate having a thickness of about 0.8 mm. It is not practical to further reduce the phase difference value because of an increase in manufacturing cost.
[0011]
An object of the present invention is to provide a transflective liquid crystal device having a configuration in which a transmission axis of a rear polarizer and a transmission axis of a reflection polarizer are set in the same direction, and a mirror reflection plate is provided under the light guide plate. Brightness unevenness and color unevenness due to residual birefringence are improved.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, a liquid crystal display device of the present invention includes a liquid crystal display panel, a light guide provided behind the liquid crystal display panel, and guiding illumination light to the liquid crystal display panel, and a liquid crystal display panel. A lower polarizer provided between the light bodies, a specular reflector provided behind the light guide, and a transmission provided in the same direction as the transmission axis of the lower polarizer, provided between the lower polarizer and the light guide. The configuration includes a reflective polarizer having an axis, and a phase difference plate provided between the reflective polarizer and the specular reflector. Further, the retardation value of the retardation plate was set to 850 nm or more. The reason why the retardation value of the retardation plate is set to 850 nm or more is a value set when the in-plane unevenness of the in-plane retardation value due to the residual birefringence of the light guide plate is about 100 nm. When it is larger than 100 nm, a larger effect can be obtained by setting the retardation value of the retardation plate to a larger value.
[0013]
Further, by arranging the optical axis of the phase difference plate in a direction at an angle of 45 ° to the transmission axis of the reflective polarizer, the effect of eliminating unevenness is exhibited most. If the angle deviates from 45 °, the effect decreases in proportion to the square of the sine.
[0014]
Alternatively, a light guide provided behind the liquid crystal display panel and guiding illumination light to the liquid crystal display panel, a lower polarizing plate provided between the liquid crystal display panel and the light guide, and provided behind the light guide plate A specular reflector, a reflective polarizer provided between the lower polarizer and the light guide, and having a transmission axis in the same direction as the transmission axis of the lower polarizer, and a light guide plate between the reflective polarizer and the specular reflector. A retardation plate having a retardation value between the maximum value and the minimum value of the in-plane retardation value when viewed from above is provided, and the optical axis of the light guide plate and the optical axis of the retardation plate are arranged so as to be orthogonal to each other. With the configuration, luminance unevenness and color unevenness are improved.
[0015]
Alternatively, a light guide provided behind the liquid crystal display panel and guiding illumination light to the liquid crystal display panel, a lower polarizing plate provided between the liquid crystal display panel and the light guide, and provided behind the light guide plate Specular reflector, provided between the lower polarizer and the light guide, a reflective polarizer having a transmission axis in the same direction as the transmission axis of the lower polarizer, between the reflective polarizer and the specular reflector, a number of A configuration including a polymer liquid crystal film composed of domains and having random alignment directions between the domains improves luminance unevenness and color unevenness.
[0016]
Alternatively, a light guide provided behind the liquid crystal display panel and guiding illumination light to the liquid crystal display panel, a lower polarizing plate provided between the liquid crystal display panel and the light guide, and provided behind the light guide plate And a reflective polarizer provided between the lower polarizing plate and the light guide, and having a transmission axis in the same direction as the transmission axis of the lower polarizing plate. The direction was set to be the same as the direction of the resin molding gate of the optical plate.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
A liquid crystal display device according to the present invention includes a light guide that guides illumination light to a liquid crystal display panel, a lower polarizing plate provided between the liquid crystal display panel and the light guide, and a mirror surface provided behind the light guide plate. A reflector, a reflective polarizer provided between the lower polarizer and the light guide, and having a transmission axis in the same direction as the transmission axis of the lower polarizer, and a phase difference plate provided between the reflective polarizer and the specular reflector It has. Further, the retardation value of the retardation plate was set to 850 nm or more.
[0018]
As described above, when a liquid crystal display device having a configuration in which a retardation plate having a retardation value of 850 nm or more is provided between a reflective polarizer and a specular reflector is observed by external light, image information is modulated by the liquid crystal display unit, and the reflective polarizer is modulated. The light passes through the retardation plate and the light guide plate, is reflected by the specular reflection plate, travels in the opposite direction to the optical path, passes through the liquid crystal display portion again to enable image display, and can be used as a reflection type.
[0019]
When the backlight is turned on in the transmission mode and used, the light of the backlight transmitted through the reflective polarizer is transmitted through the liquid crystal display unit to enable image display and can be used as a transmission type. Further, a part of the backlight light incident on the reflective polarizer is reflected as reflected light of the reflective polarizer, transmitted through the retardation plate and the light guide plate, reflected by the mirror reflector, and travels in the opposite direction to the optical path. In addition, the light is transmitted again through the liquid crystal display unit and is transmitted as a return light through the liquid crystal display unit to enable image display and increase in display luminance.
[0020]
The advantage of the above configuration is that, even when the external light and the backlight are used at the same time, the reflected light of the external light and the transmitted light of the backlight work cooperatively and become brighter than when displayed alone, that is, as a so-called semi-transmission type. Can be used. Another object of the present invention is to realize a display without luminance unevenness and color unevenness by setting the retardation value of a retardation plate disposed between a reflective polarizer and a specular reflection plate to 850 nm or more.
[0021]
Hereinafter, the operation of the retardation plate having the above effects will be described with reference to the schematic diagram of FIG. 5 illustrating the operation of the present invention. The mark x in the right half of the light guide plate 6 schematically represents a region having a large birefringence. Further, the unmarked portion in the left half represents a portion having a small birefringence. The birefringence of the mark x is represented by Δnd1, and the birefringence of the unmarked part is represented by Δnd2. Also, the phase difference value of the phase difference plate is expressed as Δndf.
[0022]
Part of the retroreflected light at the unmarked portions is shown below. The irradiation light ab of the backlight (indicated by an arrow in the figure, the same applies hereinafter) is separated by the reflective polarizer 4 into transmitted linearly polarized light a and reflected linearly polarized light b. The reflected linearly polarized light b reflected by the reflective polarizer 4 passes through the phase difference plate 5 and the light guide plate 6 and reaches the specular reflection plate 7. The arriving light is further reflected by the specular reflection plate 7, again passes through the light guide plate 6 and the phase difference plate 5, and reaches the reflection polarizer 4. Here, the reflected light (polarization state) that has reached the reflective polarizer 4 again passes through the retardation plate 5 and the light guide plate 6 twice, and thus has the sum of the phase difference values of 2 · Δndf and 2 · Δnd1. It has been converted to elliptically polarized light b1. Part of the elliptically polarized light b1 passes through the reflective polarizer 4 and becomes linearly polarized light a1, which is retroreflected light. This retroreflected light a1 exhibits an interference color corresponding to the sum of the phase difference values of 2 · Δndf and 2 · Δnd1. By the same operation, the retroreflected light A1 at the x mark portion exhibits an interference color corresponding to the sum of the phase difference between 2 · Δndf and 2 · Δnd2. The light transmitted through the liquid crystal display unit 10 is a + a1 at the x mark part and A + A1 at the non-mark part, and the difference between a + a1 and A + A1 results in uneven brightness and uneven color.
[0023]
Here, in the present invention, Δndf of the phase difference plate 5 is set to 850 nm or more. This value is sufficiently larger than the phase difference value of the residual birefringence existing in a general light guide plate. Generally, as the phase difference value increases, the interference color becomes white. FIG. 9 shows a simulation result of the interference color in the configuration of FIG. Assuming that a white LED is used as the light source and that there is no birefringence of the light guide plate, the relationship between the chromaticity x and y of the light emitted from the reflective polarizer and the phase difference value of the phase difference plate is shown. The chromaticity used here conforms to the CIE1931 color system. When the retardation value of the retardation plate is smaller than 850 nm, the variation in chromaticity xy increases. At 850 nm or more, the variation is small, and both xy converge to values of 0.325 to 0.330. This value is a value indicating white.
[0024]
As described above, if the retardation value of the retardation plate 5 is set to 850 nm or more, the residual birefringence exists in the light guide plate 6. Therefore, even if the retardation value varies in the plane of the light guide plate 6, the retardation plate 5 Since the phase difference value and the phase difference value of the light guide plate are added to increase the total phase difference value, it is possible to eliminate luminance unevenness and color unevenness.
[0025]
The above configuration is most effective when the optical axis of the phase difference plate and the optical axis of the light guide plate are added in the same direction and the phase difference values are added. However, even if the optical axis of the phase difference plate and the optical axis of the light guide plate are orthogonal to each other, a better result can be obtained as long as the phase difference value of the light guide plate is 100 nm or less as compared with the case where no phase difference plate is used.
[0026]
In FIG. 5, the retardation plate 5 is provided between the reflective polarizer 4 and the light guide plate 6. However, if the retardation plate 5 is provided between the light guide plate 6 and the specular reflection plate 7, basically the same effect as described above is obtained. Is obtained.
[0027]
Next, the above effects can be easily realized even with the following configuration. A light guide that guides illumination light to the liquid crystal display panel, a lower polarizing plate provided between the liquid crystal display panel and the light guide, a specular reflector provided behind the light guide plate, and a lower polarizing plate. A reflection polarizer provided between the light guides and having a transmission axis in the same direction as the transmission axis of the lower polarizer, and a phase difference value between the reflective polarizer and the specular reflector in a plane when the light guide plate is viewed from above. Between the maximum value and the minimum value, preferably by disposing a retardation plate having an intermediate retardation value such that the optical axis of the light guide plate and the optical axis of the retardation plate are orthogonal to each other, to reduce unevenness in brightness and unevenness in color. Has improved.
[0028]
Hereinafter, the operation of the phase difference plate that achieves the above effects will be described with reference to the schematic diagram of FIG. 10 illustrating the operation of the present invention. In the drawing, the light guide plate 6 is set up at 90 °, and the x-marks schematically represent regions with large birefringence. Unmarked portions represent portions having small birefringence. Here, in order to simplify the calculation, the birefringence of the x-marked portion was set to a phase difference value of 100 nm, and the phase difference value of the non-marked portion was set to 50 nm, and is shown in the figure. At this time, the retardation value of the retardation plate is desirably an intermediate retardation value between 100 nm and 50 nm, and is 75 nm.
[0029]
Further, the major axis direction of the ellipse in the drawing represents the optical axis direction of birefringence. Therefore, it is desirable that the optical axis of the phase difference plate is disposed orthogonal to the optical axis of the light guide plate. In the region with a large mark, the phase difference value of the light guide plate and the phase difference value of the phase difference plate are subtracted from each other in the region where the refraction is large, and a phase difference value of 25 nm is synthesized. Similarly, in the non-marked part, a phase difference value of 25 nm is synthesized in the optical axis orthogonal to the mark x. Here, referring to the simulation result of FIG. 9, the interference color at a phase difference value of 25 nm shows almost white. As a result, it is possible to improve the occurrence of uneven brightness and uneven color.
[0030]
Next, the above effects can be easily realized even with the following configuration. A light guide that guides illumination light to the liquid crystal display panel, a lower polarizing plate provided between the liquid crystal display panel and the light guide, a specular reflector provided behind the light guide plate, and a lower polarizing plate. A reflective polarizer that is provided between the light guides and has a transmission axis in the same direction as the transmission axis of the lower polarizer, and is provided between the reflective polarizer and the specular reflector, and includes a number of domains. By providing a polymer liquid crystal film having a random alignment direction, uneven brightness and uneven color of a liquid crystal display device can be improved.
[0031]
The operation of the polymer liquid crystal film having the above effects will be described below with reference to the schematic diagram of the structure of the polymer liquid crystal film of the present invention shown in FIG. The regions divided by hatching in the figure represent domains 10 having different alignment directions of liquid crystal molecules. The size of the domain is made smaller than the pixel of the liquid crystal panel, and there is a birefringent optical axis direction in the alignment direction. The retardation value having a random optical axis of the polymer liquid crystal film is combined with the birefringence retardation value of the light guide plate. As a result, the addition and subtraction of the phase difference value of the light guide plate by random optical axes are performed randomly in the plane, and as a result, the birefringence unevenness of the light guide plate is leveled.
[0032]
The domain size of the polymer liquid crystal film is smaller than the pixels of the liquid crystal panel, and the distance between the pixels of the polymer liquid crystal film and the liquid crystal panel is separated by the thickness of the liquid crystal panel substrate, polarizing plate, etc. Is reduced, and a display with improved luminance unevenness and color unevenness due to birefringence unevenness of the light guide plate can be obtained.
[0033]
Next, the above effects can be easily realized even with the following configuration. At least, a liquid crystal display unit in which an upper polarizer and a lower polarizer are arranged on a liquid crystal display panel, a reflective polarizer having a transmission axis arranged in the same direction as the transmission axis of the lower polarizer on the lower side, and further on the lower side. A backlight composed of a light guide plate, a light source and a specular reflector is arranged, and the resin molding gate direction of the light guide plate is arranged in the same direction as the transmission axis direction of the reflective polarizer, so that luminance unevenness and color unevenness are caused. Has been improved.
[0034]
The operation of obtaining the above effects will be described below with reference to the schematic diagram of the configuration of the present invention in FIG. The upper polarizer 1, the liquid crystal panel 2, and the lower polarizer 3 are integrated to form a liquid crystal display unit, and a reflective polarizer 4 is disposed below the liquid crystal display. The transmission axes of the reflective polarizer 4 and the lower polarizer 3 are arranged in the same direction. Further, a backlight composed of the light guide plate 6 and the specular reflection plate 7 is arranged therebelow. In the figure, the light source of the backlight is omitted. Since the resin molding gate direction 9 of the light guide plate 6 and the transmission axis direction of the reflective polarizer 4 are arranged in the same direction, the optical axis direction of the light guide plate matches the transmission axis direction of the reflective polarizer. .
[0035]
The liquid crystal display device having such a configuration differs from the configuration of the related art in that the optical axis direction of the light guide plate and the transmission axis direction of the reflective polarizer match. This configuration is equivalent to a polarization optical system composed of a reflection axis of a reflection polarizer, a specular reflection plate, and a transmission axis of a reflection polarizer. It is the same as being arranged in the axial direction. In this arrangement, since there is no influence of the phase difference value due to the birefringence of the light guide plate, unevenness in brightness and unevenness in color do not occur.
[0036]
【Example】
Hereinafter, embodiments of the liquid crystal display device according to the present invention will be described with reference to the drawings.
(Example 1)
FIG. 1 is a schematic diagram illustrating a cross-sectional structure of a liquid crystal display device according to the present embodiment. FIG. 6 shows transmission axes and optic axes related to polarized light at respective points (excluding the light source) in the sectional composition of FIG. 1 by arrows. As shown in FIG. 1, the upper polarizing plate 1, the liquid crystal panel 2, and the lower polarizing plate 3 are integrated to form a liquid crystal display unit 10. The liquid crystal panel can use a transmission mode represented by a TN mode. In this configuration, a specular reflection plate 7 used as a reflection plate is disposed on the back side of the light guide plate 6 of the backlight, thereby displaying a reflection mode. In order to perform specular reflection by the reflector, it is necessary to provide a diffusion layer somewhere between the upper polarizer 1 and the specular reflector 7. The transparent pressure-sensitive adhesive that bonds the liquid crystal panel 2 and the polarizing plate may have a function of a diffusion layer, or the retardation plate may have a function of a diffusion layer. Further, a scattering film may be used for the diffusion layer, and may be disposed somewhere between the upper polarizing plate 1 and the specular reflection plate 7. The diffusion layer may have both the function of diffusing the reflected light in the reflection mode and the function of diffusing the light of the backlight in the transmission mode. The diffusion layer does not need to be completely diffused to eliminate polarized light as in the prior art, and has a diffusion angle such that external light is efficiently converged toward the observer and reflected via a specular reflector. A diffusion layer having anisotropy can be used.
[0037]
As the reflective polarizer, a DBEF (Dual-Brightness-Enhancement-Film) manufactured by Sumitomo 3M Limited may be used and integrated with the liquid crystal display unit 10. However, the transmission axis of the reflective polarizer and the transmission axis of the lower polarizing plate are arranged in the same direction. The reflective polarizer only needs to have a function of increasing the transmission brightness of the liquid crystal display unit 10 by retroreflecting the light of the backlight, and a reflective film using selective reflection of circularly polarized light may be used.
[0038]
As the retardation plate 5, a uniaxially stretched film having an optical axis parallel to the film surface and produced by stretching a polymer such as polycarbonate or polyester was used. A film having a retardation value of 850 nm was arranged at an angle of 45 ° with the transmission axis of the reflective polarizer.
[0039]
The light source 8 used for the backlight uses a white LED as a light source. Acrylic is injection-molded on the light guide plate 6, and a prism is formed on one side of the light guide surface. This prism has a function of reflecting light guided inside the light guide plate toward the liquid crystal display unit 10. For the light guide plate, a method of reflecting light, such as a prism, a groove, or a hologram, can be used. However, a diffuse reflection method for eliminating polarized light such as reflection dots instead of a prism cannot be used. The reflection dot method is a method in which a white paint such as titanium white is printed.
[0040]
The residual birefringence of the light guide plate can be observed by inserting the light guide plate between crossed Nicol polarizing plates. It becomes smaller stepwise according to the flow direction of the resin from the gate portion. When the retardation value was measured with a polarizing microscope, it was 80 nm near the gate and 10 nm on the opposite side of the gate. The birefringence distribution continuously decreases as the distance from the gate increases.
[0041]
As the specular reflector 7, a surface reflector having a polyester film surface coated with silver was used. The use of a polyester film as a surface reflector eliminates the effects of birefringence. Conversely, the surface mirror may be used upside down to positively utilize the birefringence of the film. In this case, the retardation value due to the birefringence of the film needs to be 850 nm or more. Thereby, the phase difference plate 5 can be omitted and the thickness can be reduced.
[0042]
In the present invention, the mirror light reflecting plate described above is used as a reflecting plate, and despite the configuration in which external light is efficiently reflected in the reflecting mode, the light of the backlight in the transmitting mode is reflected by the reflective polarizer. The occurrence of luminance unevenness and color unevenness caused by the birefringence unevenness of the backlight that occurs when used as retroreflected light is eliminated by setting the retardation value of the retardation plate to 850 nm or more.
(Example 2)
The liquid crystal display device according to the present embodiment has a configuration in which the phase difference value of the phase difference plate in the configuration of the first embodiment is between the maximum value and the minimum value of the phase difference value of the light guide plate, preferably an intermediate phase difference value. This is a configuration that is replaced with In this configuration, the best effect can be obtained by arranging the optical axis of the light guide plate and the optical axis of the phase difference plate orthogonally. Even if the angle deviates from the right angle, the decrease in the effect is changed by the square of the sine of the deviated angle.
[0043]
The birefringence unevenness of the light guide plate can be measured with a polarizing microscope. Further, if the molding conditions of the light guide plate are stable, the unevenness is stable, so that the phase difference value and the angle of the phase difference plate can be practically determined. When there is unevenness in the optical axis direction of the light guide plate, it is desirable to arrange the optical axes of the phase difference plates orthogonally with respect to the most predominant direction in the optical axis direction. As the retardation plate, a uniaxially oriented polymer liquid crystal film can be used in addition to the uniaxially stretched film.
[0044]
In the present invention, even if the structure other than the phase difference plate is the same as that of the first embodiment, the mirror surface reflection plate is used as the reflection plate, and the light is transmitted in spite of the configuration in which the external light is efficiently reflected in the reflection mode. In the mode, the brightness unevenness and color unevenness caused by the birefringence unevenness of the backlight that occurs when the light of the backlight is used as the retroreflected light by the reflective polarizer, the phase difference value of the phase difference plate is calculated by the The occurrence is eliminated by replacing the phase difference plate with a phase difference plate having a middle value between the maximum value and the minimum value.
[0045]
(Example 3)
The liquid crystal display device of the present embodiment has a configuration in which a polymer liquid crystal film having a large number of domains and having random alignment directions between the domains is arranged instead of the retardation plate of the first embodiment. With this configuration, the polymer liquid crystal film can be arranged regardless of the optical axis of the light guide plate. The polymer liquid crystal film is manufactured using light-heat induced alignment by an axis-selective photoreaction of the photoreactive polymer liquid crystal film. A photoreactive polymer liquid crystal material is dissolved in a solvent, applied to a quartz substrate by spin coating, and irradiated with linearly polarized ultraviolet light at various domain sizes from various angles using an ultra-high pressure mercury lamp. A large number of domain sizes may be arranged in a plane using a mask for ultraviolet light, and the angle may be selected at random for exposure. After exposure, it was solidified by heat treatment and covered with a protective film to produce.
[0046]
The method for producing the polymer liquid crystal film used in the present invention is not limited to the above method, and it is sufficient that the optical axes of the domains are random. Further, the phase difference value between the domains need not always be constant. The phase difference value may be random between domains. The polymer liquid crystal film may be disposed between the reflective polarizer and the specular reflector, and may be integrated on the mirror surface of the light guide plate or the specular reflector.
[0047]
In the present invention, even if the configuration other than the phase difference plate is the same as that of the first embodiment, the mirror reflection plate is used as the reflection plate, and the light is transmitted even though the external light is efficiently reflected in the reflection mode. In the mode, the brightness unevenness and color unevenness caused by the birefringence unevenness of the backlight that occurs when using the light of the backlight as the retroreflected light with the reflective polarizer is composed of a large number of domains, and the orientation direction between the domains is random. By replacing the polymer liquid crystal film with the polymer liquid crystal film between the reflective polarizer and the specular reflection plate, the occurrence is eliminated.
[0048]
(Example 4)
A description will be given of a liquid crystal display device having the configuration of the first embodiment, in which the retardation plate is removed and the resin molding gate direction of the light guide plate is arranged in the same direction as the transmission axis direction of the reflective polarizer.
[0049]
In the present invention, the birefringence distribution generated in the flow direction at the time of resin inflow from the gate portion of the light guide plate is measured in advance, the optical axis of the residual birefringence of the light guide plate is determined, and the same direction as the transmission axis of the reflective polarizer is determined. It is desirable to be. However, the transmission axis of the upper polarizing plate of the liquid crystal display section is generally inclined by 45 ° from the viewing angle direction of 12:00 to 6:00. This is to secure a view when wearing polarized sunglasses. Therefore, when the 90 ° twist TN liquid crystal is used for the liquid crystal display unit, the transmission axis of the reflective polarizer is also inclined by 45 ° from the viewing angle direction. Therefore, the gate direction of the light guide plate is also inclined by 45 ° from the viewing angle direction.
[0050]
In addition, although the optical axis of the light guide plate is arranged in the same direction as the transmission axis of the reflective polarizer, even when the optical axis of the light guide plate is aligned with the reflection axis of the reflective polarizer, brightness unevenness and color unevenness are similarly improved. it can.
[0051]
In the present invention, the retardation plate is removed from the configuration of the first embodiment, the resin molding gate direction of the light guide plate is arranged so as to be in the same direction as the transmission axis direction of the reflective polarizer, and the mirror reflector is used as the reflector. In spite of the configuration in which external light is efficiently reflected in the reflection mode, the occurrence of uneven brightness and uneven color caused by uneven birefringence of the backlight is eliminated.
[0052]
【The invention's effect】
As described above, according to the liquid crystal display device of the present invention, despite the configuration in which the specular reflector is used as the reflector and the external light is efficiently reflected in the reflection mode, the back light is transmitted in the transmission mode. Eliminates uneven brightness and color caused by uneven birefringence of the backlight that occurs when light from a light is used as a retroreflected light by a reflective polarizer. Bright and uniform display can be easily realized in any dark place where there is no image. Therefore, the commercial value can be increased in electronic devices such as a personal computer, a camera, a mobile phone, and a clock, where the liquid crystal display device is frequently used in the consumer goods market.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a cross-sectional structure of a display device of the present invention.
FIG. 2 is an explanatory diagram of a cause of occurrence of unevenness in a conventional technique.
FIG. 3 is a schematic diagram illustrating birefringence unevenness when the light guide plate is viewed from above.
FIG. 4 is a schematic diagram showing a birefringence distribution of a light guide plate when a gate portion is arranged at a corner.
FIG. 5 is a schematic diagram illustrating the operation of the present invention.
FIG. 6 is a diagram in which a transmission axis and an optical axis related to polarized light are represented by arrows.
FIG. 7 is a schematic view showing the structure of the polymer liquid crystal film of the present invention.
FIG. 8 is a schematic diagram of the configuration of the present invention.
FIG. 9 is a diagram illustrating a simulation result of an interference color.
FIG. 10 is a schematic diagram illustrating the operation of the present invention.
[Explanation of symbols]
1 Upper polarizing plate
2 Liquid crystal panel
3 Lower polarizing plate
4 Reflective polarizer
5 Phase difference plate
6 Light guide plate
7 Mirror reflector
8 light source
9 Gate section

Claims (7)

液晶表示パネルと、
前記液晶表示パネルの背後に設けられ、前記液晶表示パネルに照明光を導光する導光体と、
前記液晶表示パネルと前記導光体の間に設けられた下偏光板と、
前記導光板の背後に設けられた鏡面反射板と、
前記下偏光板と前記導光体の間に設けられ、前記下偏光板の透過軸と同一方向の透過軸を有する反射偏光子と、
前記反射偏光子と前記鏡面反射板の間に設けられた位相差板と、
を備えることを特徴とする液晶表示装置。
A liquid crystal display panel,
A light guide that is provided behind the liquid crystal display panel and guides illumination light to the liquid crystal display panel;
A lower polarizing plate provided between the liquid crystal display panel and the light guide,
A mirror reflector provided behind the light guide plate,
A reflective polarizer provided between the lower polarizer and the light guide, and having a transmission axis in the same direction as the transmission axis of the lower polarizer,
A retardation plate provided between the reflective polarizer and the specular reflector,
A liquid crystal display device comprising:
前記位相差板の位相差値が850nm以上であることを特徴とする請求項1に記載の液晶表示装置。2. The liquid crystal display device according to claim 1, wherein the retardation value of the retardation plate is 850 nm or more. 前記位相差板の光学軸が、前記反射偏光子の透過軸に対して45°の方向に設定されたことを特徴とする請求項1または2に記載の液晶表示装置。The liquid crystal display device according to claim 1, wherein an optical axis of the retardation plate is set at a direction of 45 ° with respect to a transmission axis of the reflective polarizer. 前記位相差板の位相差値が、前記導光体の前記照明光が出射する面内における位相差値の最大値と最小値の間の値であり、
前記位相差板の光学軸が前記導光体の光学軸と直交することを特徴とする請求項1に記載の液晶表示装置。
The phase difference value of the phase difference plate is a value between a maximum value and a minimum value of a phase difference value in a plane where the illumination light of the light guide is emitted,
The liquid crystal display device according to claim 1, wherein an optical axis of the phase difference plate is orthogonal to an optical axis of the light guide.
前記位相差板の位相差値は、前記照明光が出射される前記導光体面内の位相差値の最大値と最小値の中間の値であることを特徴とする請求項4に記載の表示装置。The display according to claim 4, wherein the phase difference value of the phase difference plate is an intermediate value between the maximum value and the minimum value of the phase difference value in the light guide surface from which the illumination light is emitted. apparatus. 液晶表示パネルと、
前記液晶表示パネルの背後に設けられ、前記液晶表示パネルに照明光を導光する導光体と、
前記液晶表示パネルと前記導光体の間に設けられた下偏光板と、
前記導光板の背後に設けられた鏡面反射板と、
前記下偏光板と前記導光体の間に設けられ、前記下偏光板の透過軸と同一方向の透過軸を有する反射偏光子と、
前記反射偏光子と前記鏡面反射板の間に設けられるとともに、多数のドメインからなり、各ドメイン間の配向方向がランダムな高分子液晶フィルムを備えることを特徴とする液晶表示装置。
A liquid crystal display panel,
A light guide that is provided behind the liquid crystal display panel and guides illumination light to the liquid crystal display panel;
A lower polarizing plate provided between the liquid crystal display panel and the light guide,
A mirror reflector provided behind the light guide plate,
A reflective polarizer provided between the lower polarizer and the light guide, and having a transmission axis in the same direction as the transmission axis of the lower polarizer,
A liquid crystal display device comprising a polymer liquid crystal film provided between the reflective polarizer and the specular reflection plate, comprising a number of domains, and having a random orientation between the domains.
液晶表示パネルと、
前記液晶表示パネルの観察方向とは逆側に設けられた下偏光板と、
前記液晶表示パネルの背後に設けられ、前記液晶表示パネルに照明光を導光する導光体と、
前記導光板の背後に設けられた鏡面反射板と、
前記下偏光板と前記導光体の間に設けられ、前記下偏光板の透過軸と同一方向の透過軸を有する反射偏光子を備えるとともに、
前記反射偏光子の透過軸方向が前記導光板の樹脂成形ゲート方向と同一方向に設定されたことを特徴とする液晶表示装置。
A liquid crystal display panel,
A lower polarizing plate provided on the side opposite to the viewing direction of the liquid crystal display panel,
A light guide that is provided behind the liquid crystal display panel and guides illumination light to the liquid crystal display panel;
A mirror reflector provided behind the light guide plate,
A lower polarizer and a reflective polarizer having a transmission axis in the same direction as the transmission axis of the lower polarizer, provided between the light guide,
A liquid crystal display device, wherein a transmission axis direction of the reflective polarizer is set in the same direction as a resin molding gate direction of the light guide plate.
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