JP3609563B2

JP3609563B2 - Wide-field polarizing plate

Info

Publication number: JP3609563B2
Application number: JP31284496A
Authority: JP
Inventors: 雄二済木; 裕之吉見; 清司梅本; 伸一佐々木
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 1996-11-08
Filing date: 1996-11-08
Publication date: 2005-01-12
Anticipated expiration: 2016-11-08
Also published as: JPH10142423A

Description

【０００１】
【発明の技術分野】
本発明は、良視認の視角範囲が広い液晶表示装置を形成しうる広視野偏光板に関する。
【０００２】
【従来の技術】
低電圧、低消費電力でＩＣ回路と直結でき、表示機能が多様で軽量性等に優れるなどの多くの特長に着目されてワードプロセッサやパーソナルコンピュータ等のＯＡ機器やテレビジョン、カーナビゲーションモニタや航空機コックピット用モニタなどの種々の表示手段として液晶表示装置が広く普及しているが、ＣＲＴに比べて良視認の視角範囲の狭さが指摘されて久しい。
【０００３】
前記視角範囲の狭さは、液晶に特有の光学的異方性が視認性の視野角特性に影響して、偏光層を介して液晶セルに入射した直線偏光が楕円偏光化したり、方位角が変化することに原因があると考えられている。すなわち、液晶セルを透過した当該偏光状態の表示光をそのまま視認側の偏光層に入射させると、視野角すなわち正面（垂直）方向を基準とした見る角度の増大に伴い透過率が低下して表示明度が不足したり、階調が反転したり、着色化等の色変化を生じるなどの視認性の低下を招くものと考えられている。
【０００４】
従来、液晶表示装置の良視認領域の拡大方法、すなわち視角範囲の拡大方法としては、位相差板を用いる方法が知られており、その位相差板として種々のものが提案されている（特開平４−２２９８２８号公報、特開平４−２５８９２３号公報、特開平６−７５１１６公報、特開平６−１７４９２０公報、特開平６−２２２２１３公報）。しかしながらいずれの場合にも、良視認の視角範囲の拡大性の点で改善効果に乏しく満足できるものではなかった。
【０００５】
【発明の技術的課題】
本発明は、液晶セルに対して配置する偏光層を改善することにより、液晶表示装置における良視認領域を拡大することを課題とする。
【０００６】
【課題の解決手段】
本発明は、偏光層の片側に、遅相軸方向の屈折率をｎ_ｓ、進相軸方向の屈折率をｎ_ｆ、厚さ方向の屈折率をｎ_ｚ、層厚をｄとして、式：（ｎ_ｓ−ｎ_ｚ）ｄで定義される厚さ方向位相差が３００ｎｍ以下で、式：（ｎ_ｓ−ｎ_ｆ）ｄで定義される面内位相差が２０ｎｍ以下の複屈折層Ａと、当該面内位相差が５０〜２００ｎｍで、式：（ｎ_ｓ−ｎ_ｚ）／（ｎ_ｓ−ｎ_ｆ）で定義されるＮ_ｚが０．８〜３．５の複屈折層Ｂとを有し、かつその複屈折層Ｂの遅相軸と前記偏光層の透過軸とが平行関係又は直交関係にあることを特徴とする広視野偏光板を提供するものである。
【０００７】
【発明の効果】
複屈折層Ａと複屈折層Ｂからなる重畳複屈折層を偏光層の片側に配置し、かつ偏光層の透過軸と複屈折層Ｂの遅相軸を平行関係又は直交関係とした上記の構成により、偏光層面に垂直な正面方向では各複屈折層の位相差の影響を受けずに輝度やコントラストの低下を防止でき、かつ複屈折層Ａ，Ｂを介し液晶セルの複屈折性による直線偏光の状態変化を補償して、着色化等の色変化や階調反転がなくてコントラストや明るさに優れる良視認性の領域を拡大でき、視角範囲の広い液晶表示装置を得ることができる。
【０００８】
【発明の実施形態】
本発明の広視野偏光板は、偏光層の片側に、遅相軸方向の屈折率をｎ_ｓ、進相軸方向の屈折率をｎ_ｆ、厚さ方向の屈折率をｎ_ｚ、層厚をｄとして、式：（ｎ_ｓ−ｎ_ｚ）ｄで定義される厚さ方向位相差が３００ｎｍ以下で、式：（ｎ_ｓ−ｎ_ｆ）ｄで定義される面内位相差が２０ｎｍ以下の複屈折層Ａと、当該面内位相差が５０〜２００ｎｍで、式：（ｎ_ｓ−ｎ_ｚ）／（ｎ_ｓ−ｎ_ｆ）で定義されるＮ_ｚが０．８〜３．５の複屈折層Ｂとを有し、かつその複屈折層Ｂの遅相軸と前記偏光層の透過軸とが平行関係又は直交関係にあるものである。その例を図１、図２に示した。１が偏光層、３が複屈折層Ａ３１と複屈折層Ｂ３２からなる重畳複屈折層であり、矢印が透過軸、遅相軸の方向を表している。なお２は、接着剤層である。
【０００９】
偏光層としては、所定の偏光状態の光を得ることができる適宜なものを用いうる。就中、直線偏光状態の透過光を得ることのできるものが好ましい。その例としては、ポリビニルアルコール系フィルムや部分ホルマール化ポリビニルアルコール系フィルム、エチレン・酢酸ビニル共重合体系部分ケン化フィルムの如き親水性高分子フィルムにヨウ素及び／又は二色性染料を吸着させて延伸したもの、ポリビニルアルコールの脱水処理物やポリ塩化ビニルの脱塩酸処理物の如きポリエン配向フィルム等からなる偏光フィルムなどがあげられる。
【００１０】
偏光層、就中、偏光フィルムは、その片側又は両側に透明保護層を有するものであってもよい。その場合、透明保護層に所定の複屈折特性を示すものを用いて本発明における複屈折層Ａ又はＢを兼ねさせることもできる。また偏光層は、反射層を有する反射型のものであってもよい。反射型の偏光層は、視認側（表示側）からの入射光を反射させて表示するタイプの液晶表示装置などを形成するためのものであり、バックライト等の光源の内蔵を省略できて液晶表示装置の薄型化をはかりやすいなどの利点を有する。
【００１１】
透明保護層は、プラスチックの塗布層や保護フィルムの積層物などとして適宜に形成でき、その形成には透明性や機械的強度、熱安定性や水分遮蔽性等に優れるプラスチックなどが好ましく用いうる。その例としては、ポリエステル系樹脂やアセテート系樹脂、ポリエーテルスルホン系樹脂やポリカーボネート系樹脂、ポリアミド系樹脂やポリイミド系樹脂、ポリオレフィン系樹脂やアクリル系樹脂、あるいはアクリル系やウレタン系、アクリルウレタン系やエポキシ系やシリコーン系等の熱硬化型、ないし紫外線硬化型の樹脂などがあげられる。透明保護層は、微粒子の含有によりその表面が微細凹凸構造に形成されていてもよい。
【００１２】
反射型偏光層の形成は、必要に応じ透明樹脂層等を介して偏光層の片面に金属等からなる反射層を付設する方式などの適宜な方式で行うことができる。その具体例としては、必要に応じマット処理した保護フィルム等の透明樹脂層の片面に、アルミニウム等の反射性金属からなる箔や蒸着膜を付設したものや、前記透明樹脂層の微粒子含有による表面微細凹凸構造の上に蒸着方式やメッキ方式などの適宜な方式で金属反射層を付設したものなどがあげられる。
【００１３】
複屈折層Ａ，Ｂとしては、複屈折による所定の位相差等を示す適宜なものを用いうる。就中、光透過性の各種フィルムを延伸処理等により複屈折性を付与したものや、液晶ポリマーの配向膜、あるいは基材の配向膜上等に液晶ポリマー等の異方性材料を配向させたものなどが好ましく用いうる。特に、光透過率が７０％以上、好ましくは８０％以上、より好ましくは８５％以上の透光性に優れるフィルムに複屈折性を付与したものが好ましい。
【００１４】
前記の透光性フィルムとしては、ポリカーボネートやポリアリレート、ポリスルホンやポリエチレンテレフタレート、ポリエーテルスルホンやポリビニルアルコール、ポリエチレンないしポリプロピレンの如きポリオレフィンやトリアセチルセルロースの如きセルロース系ポリマー、ポリスチレンやポリメチルメタクリレート、ポリ塩化ビニルやポリ塩化ビニリデン、ポリアミドなどからなるフィルムが特に好ましい。
【００１５】
透光性フィルムに複屈折性を付与する配向処理は、例えば自由端又は固定端による一軸延伸処理や二軸延伸処理などの適宜な方式で行うことができる。本発明にては、厚さ方向に配向したフィルムや、その厚さ方向の主屈折率の方向がフィルムの法線方向に対して傾斜したものなども複屈折層の形成に用いうる。延伸方式や延伸条件等の配向処理条件の制御、形成材料の変更などにより複屈折による位相差特性を調節でき、本発明に用いうる複屈折層を形成することができる。また本発明で用いる複屈折層Ａ，Ｂは、複数の位相差板を積層して所定の位相差特性を示すように形成されたものであってもよい。
【００１６】
本発明において偏光層の片側に配置する複屈折層は、複屈折層Ａと複屈折層Ｂの重畳複屈折層にて形成され、その複屈折層Ａは、厚さ方向位相差が３００ｎｍ以下で面内位相差が２０ｎｍ以下のものとされる。また複屈折層Ｂは、面内位相差が５０〜２００ｎｍでＮ_ｚが０．８〜３．５のものとされ、かつ複屈折層Ｂはその遅相軸が偏光層の透過軸と平行関係又は直交関係となるように配置される。なお前記の厚さ方向位相差は、遅相軸方向の屈折率をｎ_ｓ、進相軸方向の屈折率をｎ_ｆ、厚さ方向の屈折率をｎ_ｚ、層厚をｄとして、式：（ｎ_ｓ−ｎ_ｚ）ｄで定義される。また面内位相差（△ｎｄ）は、式：（ｎ_ｓ−ｎ_ｆ）ｄで定義され、Ｎ_ｚは、式：（ｎ_ｓ−ｎ_ｚ）／（ｎ_ｓ−ｎ_ｆ）で定義される。各屈折率は、ナトリウムＤ線に基づく。
【００１７】
前記において、偏光層の透過軸に対する複屈折層Ｂの遅相軸の平行関係又は直交関係による配置は、上記したように正面方向における各複屈折層の位相差の影響を防止して輝度やコントラストの低下の回避を目的とする。また複屈折層の重畳化は、前記の平行又は直交関係の配置状態において、視角が正面方向よりズレた場合に複屈折層Ｂの遅相軸方向が変化して当該平行関係又は直交関係にズレが生じ、そのズレ量に応じて複屈折層の光学異方性が発現することから、複屈折層Ａ及び複屈折層Ｂの面内位相差とＮ_ｚに基づいて前記した遅相軸の変化量を制御し、複屈折層における光学異方性の発現量の調節を目的とする。
【００１８】
すなわち前記は、複屈折層Ｂの面内位相差とＮ_ｚを最適化しつつ、面内位相差が可及的に少ない複屈折層Ａを介して厚さ方向位相差を制御することが良視認の視角範囲拡大に有利であることを意味する。良視認の視角範囲拡大の点より好ましい複屈折層Ａは、面内位相差が１８ｎｍ以下、就中１５ｎｍ以下、特に０〜１０ｎｍで、厚さ方向位相差が２５０ｎｍ以下、就中２２０ｎｍ以下、特に３０〜２００ｎｍのものである。面内位相差が２０ｎｍを超える複屈折層Ａ、又は厚さ方向位相差が３００ｎｍを超える複屈折層Ａでは、前記した遅相軸変化の制御性に乏しくて良視認の視角範囲の拡大力に乏しくなる。
【００１９】
また良視認の視角範囲拡大の点より好ましい複屈折層Ｂは、面内位相差が６０〜１９０ｎｍ、就中８０〜１７０ｎｍ、特に１００〜１４０ｎｍで、Ｎ_ｚが３．３以下、就中３．０以下、特に２．８以下のものである。その面内位相差が５０ｎｍ未満では視角の変化に対する補償効果に乏しい場合があり、２００ｎｍを超えると複屈折率差の波長分散で着色化等の色変化を生じる場合がある。またＮ_ｚが０．８未満や３．５を超える値では、視角による遅相軸の変化が大きくなって補償できる視角範囲が狭くなり、広視野角化が困難となる。
【００２０】
偏光層に対する複屈折層Ａ，Ｂの配置順序は任意であるが、得られる広視野偏光板の薄型化等の点よりは、図例の如く複屈折層Ａ３１を偏光層側として偏光層１の透明保護層を兼ねさせたものが好ましい。その場合、複屈折層Ａの形成には位相差特性等の点よりトリアセチルセルロースフィルムが特に好ましく用いられる。なお複屈折層Ａ，Ｂの厚さは、上記の如く面内位相差と関係することから目的とする位相差特性などにより適宜に決定できるが、一般には５〜５００μｍ、就中１０〜３５０μｍ、特に２０〜２００μｍとされる。
【００２１】
本発明の広視野偏光板は、液晶セルの複屈折による視角特性の補償に好ましく用いうるが、その形成は液晶表示装置の製造過程で複屈折層Ａ，Ｂと偏光層を順次別個に積層する方式や、予め複屈折層Ａと複屈折層Ｂと偏光層の適宜な組合せからなる２層又は３層の積層物としてそれを用いる方式などの適宜な方式で行うことができる。後者の事前積層化方式が、品質の安定性や積層作業性等に優れて液晶表示装置の製造効率を向上させうる利点などがある。
【００２２】
偏光層の片側への複屈折層Ｂの積層配置等に際しては、その偏光層の透過軸と複屈折層Ｂの遅相軸とが平行関係又は直交関係となるように行われるが、その平行関係又は直交関係は厳密な意味での平行又は直交状態に限定されず、作業上の配置誤差などは許容される。また透過軸や遅相軸の方向にバラツキがある場合などには全体としての平均方向に基づいて平行関係又は直交関係に配置される。
【００２３】
上記において、偏光層と複屈折層Ａ，Ｂの積層に際しては、必要に応じ接着剤等を介して固定することができる。軸関係のズレ防止等の点よりは接着固定することが好ましい。接着には、例えばアクリル系やシリコーン系、ポリエステル系やポリウレタン系、ポリエーテル系やゴム系等の透明な感圧接着剤などの適宜な接着剤を用いることができ、その種類については特に限定はない。光学特性の変化を防止する点などよりは、硬化や乾燥の際に高温のプロセスを要しないものが好ましく、長時間の硬化処理や乾燥時間を要しないものが望ましい。また加熱や加湿条件下に剥離等を生じないものが好ましい。
【００２４】
かかる点より、（メタ）アクリル酸ブチルや（メタ）アクリル酸メチル、（メタ）アクリル酸エチルや（メタ）アクリル酸の如きモノマーを成分とする重量平均分子量が１０万以上で、ガラス転移温度が０℃以下のアクリル系ポリマーからなるアクリル系感圧接着剤が特に好ましく用いうる。またアクリル系感圧接着剤は、透明性や耐候性や耐熱性などに優れる点よりも好ましい。なお屈折率が異なるものを積層する場合には、反射損の抑制などの点より中間の屈折率を有する接着剤等が好ましく用いられる。
【００２５】
接着剤には、必要に応じて例えば天然物や合成物の樹脂類、ガラス繊維やガラスビーズ、金属粉やその他の無機粉末等からなる充填剤や顔料、着色剤や酸化防止剤などの適宜な添加剤を配合することもできる。また微粒子を含有させて光拡散性を示す接着剤層とすることもできる。
【００２６】
なお上記した偏光層や複屈折層Ａ，Ｂ、透明保護層や接着剤層などの各層は、例えばサリチル酸エステル系化合物やベンゾフェノール系化合物、ベンゾトリアゾール系化合物やシアノアクリレート系化合物、ニッケル錯塩系化合物等の紫外線吸収剤で処理する方式などにより紫外線吸収能をもたせることもできる。
【００２７】
本発明の広視野偏光板を用いての液晶表示装置の形成は、従来に準じて行いうる。すなわち液晶表示装置は一般に、液晶セルと偏光層と光学補償を目的とした複屈折層、及び必要に応じての照明システム等の構成部品を適宜に組立てて駆動回路を組込むことなどにより形成されるが、本発明においては当該広視野偏光板を液晶セルの少なくとも片側に設ける点を除いて特に限定はなく、従来に準じうる。
【００２８】
従って、液晶セルの片側又は両側に広視野偏光板を配置した液晶表示装置や、照明システムにバックライトあるいは反射板を用いたものなどの適宜な液晶表示装置を形成することができる。その場合、複屈折層Ａ，Ｂは液晶セルと偏光層との間、特に視認側の偏光層との間に配置することが補償効果の点などより好ましい。なお広視野偏光板の実用に際しては、液晶表示装置を形成するための他の光学素子等との積層物などの適宜な形態で用いることができる。
【００２９】
図３、図４に広視野偏光板を用いた液晶表示装置の構成例を示した。４が液晶セル、５がバックライトシステム、６が反射層である。なお７は光拡散板である。図３のものは両側に広視野偏光板を配置したバックライト型照明システムのものであり、図４のものは片側にのみ広視野偏光板を配置した反射型照明システムのものである。
【００３０】
前記において液晶表示装置の形成部品は、積層一体化状態又は適宜な分離状態にあってよい。また液晶表示装置の形成に際しては、例えば拡散板やアンチグレア層、反射防止膜、保護層や保護板などの適宜な光学素子を適宜に配置することができる。本発明の広視野偏光板は、ＴＮ型やＳＴＮ型等の複屈折を示す液晶セルを用いたＴＦＴ型やＭＩＭ型等の種々の表示装置に好ましく用いうる。
【００３１】
【実施例】
実施例１
厚さ８０μｍのポリビニルアルコールフィルムをヨウ素水溶液中で５倍に延伸処理したのち乾燥させて得た偏光フィルムの片面に、厚さ１５μｍのポリビニルアルコール系接着剤層を介して、トリアセチルセルロースフィルムの二軸延伸物からなる△ｎｄ：６ｎｍ（Ｎ_ｚ：１０）、厚さ方向位相差６０ｎｍの複屈折フィルムＡを接着し、かつその上に厚さ２０μｍのアクリル系粘着層を介して、厚さ６０μｍのポリカーボネートフィルムを１６０℃の雰囲気下、周速の異なるロール間を通過させて１．０８倍に延伸処理して得た△ｎｄ：１１５ｎｍ、Ｎ_ｚ：１．０の複屈折フィルムＢを接着して広視野偏光板を得た。なお接着処理は、偏光フィルムの透過軸と複屈折フィルムＢの遅相軸が平行関係となるように行った。
【００３２】
実施例２
複屈折フィルムＢとして、厚さ６０μｍのポリカーボネートフィルムを１６０℃の雰囲気下、二軸延伸処理して得た△ｎｄ：８０ｎｍ、Ｎ_ｚ：２．０のものを用いたほかは、実施例１に準じて広視野偏光板を得た。
【００３３】
比較例１
実施例１に準じて得た偏光フィルムのみを用いた。
【００３４】
比較例２
複屈折フィルムＡの外側に、アクリル系粘着層と複屈折フィルムＢを有しない形態としたほかは、実施例１に準じて偏光板を得た。
【００３５】
比較例３
複屈折フィルムＡを用いずに、偏光フィルムと複屈折フィルムＢをアクリル系粘着層を介して直接接着したほかは、実施例１に準じて偏光板を得た。
【００３６】
比較例４
複屈折フィルムＢとして、厚さ６０μｍのポリカーボネートフィルムを１６０℃の雰囲気下、周速の異なるロール間を通過させて１．１５倍に延伸処理して得た△ｎｄ：３５０ｎｍ、Ｎ_ｚ：１．０のものを用いたほかは、実施例１に準じて偏光板を得た。
【００３７】
比較例５
複屈折フィルムＢとして、厚さ６０μｍのポリカーボネートフィルムを１６０℃の雰囲気下、周速の異なるロール間を通過させて１．０３倍に延伸処理して得た△ｎｄ：４０ｎｍ、Ｎ_ｚ：１．０のものを用いたほかは、実施例１に準じて偏光板を得た。
【００３８】
比較例６
複屈折フィルムＡとして、厚さ６０μｍのポリカーボネートフィルムを１６０℃の雰囲気下に二軸延伸処理して得た△ｎｄ：２０ｎｍ、厚さ方向位相差３５０ｎｍのものを用いたほかは、実施例１に準じて偏光板を得た。
【００３９】
評価試験
実施例、比較例で得た（広視野）偏光板をＴＦＴ型液晶セルの両側（フロント／リア）に配置し、黒つぶれ（表示の黒色化）や白呆け（表示の白色化）によるコントラストの低下及び階調の反転を生じない良視認を示す左右方向及び上下方向の視角範囲を調べた。
【００４０】
前記の結果を次表に示した。

【００４１】
表より、実施例と偏光フィルムのみの比較例１との対比より、左右の視角範囲が格段に改善されており、上下方向の視角範囲も若干改善されていることがわかる。また比較例２〜６との対比より、所定の複屈折特性を満足する層を重畳化することが視角範囲の拡大に有利であることがわかる。なお実施例と比較例１における視認不良は、階調の反転による。
【図面の簡単な説明】
【図１】広視野偏光板例の部分断面斜視図
【図２】他の広視野偏光板例の部分断面斜視図
【図３】液晶表示装置例の断面図
【図４】他の液晶表示装置例の断面図
【符号の説明】
１：偏光層
２：接着剤層
３：重畳複屈折層
３１：複屈折層Ａ
３２：複屈折層Ｂ
４：液晶セル[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wide-field polarizing plate that can form a liquid crystal display device with a wide viewing angle range for good visual recognition.
[0002]
[Prior art]
Focusing on many features such as low voltage, low power consumption, direct connection to IC circuits, various display functions and excellent light weight, OA equipment such as word processors and personal computers, televisions, car navigation monitors and aircraft cockpits Liquid crystal display devices have been widely used as various display means such as monitors, but it has long been pointed out that a narrow viewing angle range is better than CRT.
[0003]
The narrow viewing angle range is due to the fact that the optical anisotropy peculiar to liquid crystals affects the viewing angle characteristics of visibility, so that linearly polarized light incident on the liquid crystal cell via the polarizing layer becomes elliptically polarized or the azimuth angle is It is thought that there is a cause to change. In other words, when display light in the polarization state that has passed through the liquid crystal cell is directly incident on the polarizing layer on the viewing side, the transmittance decreases as the viewing angle, that is, the viewing angle based on the front (vertical) direction, increases. It is considered that the visibility is deteriorated such that the lightness is insufficient, the gradation is reversed, or a color change such as coloring is caused.
[0004]
Conventionally, as a method for enlarging a good viewing area of a liquid crystal display device, that is, a method for enlarging a viewing angle range, a method using a phase difference plate has been known, and various types of phase difference plates have been proposed (Japanese Patent Laid-Open No. Hei. JP-A-4-229828, JP-A-4-258923, JP-A-6-75116, JP-A-6-174920, JP-A-6-222213). However, in either case, the improvement effect is poor and satisfactory in terms of the expandability of the viewing angle range with good visual recognition.
[0005]
[Technical Problem of the Invention]
This invention makes it a subject to expand the good visual recognition area | region in a liquid crystal display device by improving the polarizing layer arrange | positioned with respect to a liquid crystal cell.
[0006]
[Means for solving problems]
In the present invention, on one side of the polarizing layer, the refractive index in the slow axis direction is n _s , the refractive index in the fast axis direction is n _f , the refractive index in the thickness direction is n _z , and the layer thickness is d. _(n s _-n z) thickness retardation defined by d is at 300nm following _formula: a (n s _-n f) the birefringent layer plane retardation following 20nm defined by d a, in the in-plane retardation is 50 to 200 nm, _{_{_{wherein: (n s -n z) /}}} (n s -n f) n z defined by the chromatic and birefringent layer B of 0.8 to 3.5 In addition, the present invention provides a wide-field polarizing plate characterized in that the slow axis of the birefringent layer B and the transmission axis of the polarizing layer are parallel or orthogonal.
[0007]
【The invention's effect】
The above configuration in which a superimposed birefringent layer composed of a birefringent layer A and a birefringent layer B is disposed on one side of the polarizing layer, and the transmission axis of the polarizing layer and the slow axis of the birefringent layer B are in a parallel relationship or an orthogonal relationship. Therefore, in the front direction perpendicular to the plane of the polarizing layer, it is possible to prevent a decrease in luminance and contrast without being affected by the phase difference of each birefringent layer, and linear polarization due to the birefringence of the liquid crystal cell via the birefringent layers A and B. By compensating for this state change, it is possible to expand a good visibility region that is excellent in contrast and brightness without color change such as coloring or gradation inversion, and a liquid crystal display device with a wide viewing angle range can be obtained.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The wide-field polarizing plate of the present invention has, on one side of the polarizing layer, the refractive index in the slow axis direction is n _s , the refractive index in the fast axis direction is n _f , the refractive index in the thickness direction is n _z , and the layer thickness is as d, the _formula: (n s _-n z) thickness retardation defined by d is at 300nm following _formula: (n s _-n f) double-plane retardation is defined below 20nm in d refractive layer a, the in-plane retardation is at 50 to 200 nm, _wherein: _(n s -n z) _/ birefringence _(n s -n _f) is defined by _{n z} is 0.8 to 3.5 And the slow axis of the birefringent layer B and the transmission axis of the polarizing layer are in a parallel or orthogonal relationship. Examples thereof are shown in FIGS. Reference numeral 1 denotes a polarizing layer, 3 denotes a superimposed birefringent layer composed of a birefringent layer A31 and a birefringent layer B32, and arrows indicate the directions of the transmission axis and the slow axis. Reference numeral 2 denotes an adhesive layer.
[0009]
As the polarizing layer, an appropriate layer that can obtain light in a predetermined polarization state can be used. In particular, those capable of obtaining transmitted light in a linearly polarized state are preferable. Examples include stretching by adsorbing iodine and / or dichroic dyes to hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And a polarizing film comprising a polyene oriented film such as a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product.
[0010]
The polarizing layer, especially the polarizing film, may have a transparent protective layer on one side or both sides thereof. In that case, the transparent protective layer having a predetermined birefringence characteristic can also be used as the birefringent layer A or B in the present invention. The polarizing layer may be a reflective type having a reflective layer. The reflective polarizing layer is for forming a liquid crystal display device of a type that reflects incident light from the viewing side (display side) and displays the liquid crystal display device. It has an advantage that the display device can be easily thinned.
[0011]
The transparent protective layer can be appropriately formed as a plastic coating layer, a laminate of protective films, and the like, and plastics excellent in transparency, mechanical strength, thermal stability, moisture shielding properties and the like can be preferably used for the formation. Examples include polyester resins, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acrylic resins, acrylic resins, urethane resins, acrylic urethane resins, Examples thereof include thermosetting resins such as epoxy and silicone resins, and ultraviolet curable resins. The surface of the transparent protective layer may be formed in a fine concavo-convex structure by containing fine particles.
[0012]
The reflective polarizing layer can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is attached to one surface of the polarizing layer via a transparent resin layer or the like as necessary. Specific examples thereof include a surface of a transparent resin layer such as a protective film that is mat-treated if necessary, with a foil or vapor deposition film made of a reflective metal such as aluminum, or the surface of the transparent resin layer containing fine particles. For example, a metal reflective layer provided on the fine concavo-convex structure by an appropriate method such as vapor deposition or plating.
[0013]
As the birefringent layers A and B, appropriate ones exhibiting a predetermined phase difference or the like due to birefringence can be used. In particular, anisotropic materials such as liquid crystal polymers were aligned on light transmissive films with birefringence imparted by stretching treatment, liquid crystal polymer alignment films, or substrate alignment films. A thing etc. can be used preferably. In particular, a film having a light transmittance of 70% or more, preferably 80% or more, and more preferably 85% or more and having a birefringence imparted to a film having excellent translucency is preferable.
[0014]
Examples of the translucent film include polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyether sulfone, polyvinyl alcohol, polyolefins such as polyethylene and polypropylene, cellulose polymers such as triacetyl cellulose, polystyrene, polymethyl methacrylate, polychlorinated. A film made of vinyl, polyvinylidene chloride, polyamide or the like is particularly preferable.
[0015]
The alignment treatment for imparting birefringence to the translucent film can be performed by an appropriate method such as a uniaxial stretching treatment or a biaxial stretching treatment using a free end or a fixed end. In the present invention, a film oriented in the thickness direction or a film in which the direction of the main refractive index in the thickness direction is inclined with respect to the normal direction of the film can be used for forming the birefringent layer. The retardation characteristics due to birefringence can be adjusted by controlling the orientation treatment conditions such as the stretching method and stretching conditions, and changing the forming material, and a birefringent layer that can be used in the present invention can be formed. The birefringent layers A and B used in the present invention may be formed by laminating a plurality of retardation plates so as to exhibit predetermined retardation characteristics.
[0016]
In the present invention, the birefringent layer disposed on one side of the polarizing layer is formed by a superimposed birefringent layer of the birefringent layer A and the birefringent layer B, and the birefringent layer A has a thickness direction retardation of 300 nm or less. The in-plane retardation is set to 20 nm or less. The birefringent layer B has an in-plane retardation is assumed _{N z} is 0.8 to 3.5 at 50 to 200 nm, and the birefringent layer B is its slow axis parallel relationship with the transmission axis of the polarizing layer Or it arrange | positions so that it may become orthogonal relationship. Note the thickness retardation of said, a refractive index in a slow axis direction n _s, a refractive index n _f of the fast axis _direction, a refractive index in the thickness direction n _z, the layer thickness as d, the formula: It is defined by (n _s −n _z ) d. The in-plane retardation (△ nd) of the _formula: as defined in _{(n s -n f) d,} N z is the _formula: as defined in _{_{(n s -n z) / (}} n s -n f) . Each refractive index is based on the sodium D line.
[0017]
In the above, the arrangement based on the parallel or orthogonal relationship of the slow axis of the birefringent layer B with respect to the transmission axis of the polarizing layer prevents the influence of the phase difference of each birefringent layer in the front direction as described above, thereby improving the brightness and contrast. The purpose is to avoid the decrease of In addition, when the birefringent layer is superimposed, the slow axis direction of the birefringent layer B is changed when the viewing angle is deviated from the front direction in the parallel or orthogonal arrangement state, and the parallel or orthogonal relationship is deviated. occurs, that in accordance with the deviation amount from expressing optical anisotropy of the birefringent layer, the change of the slow axis which is on the basis of the in-plane retardation and N _z of the birefringent layer a and birefringence layer B The amount is controlled to adjust the amount of optical anisotropy in the birefringent layer.
[0018]
That said, while optimizing plane retardation and N _z of the birefringent layer B, it is good to control the thickness retardation via an in-plane retardation is as possible small birefringent layer A viewing This is advantageous for expanding the viewing angle range. The birefringent layer A preferable from the viewpoint of widening the viewing angle range for good visual recognition has an in-plane retardation of 18 nm or less, especially 15 nm or less, particularly 0 to 10 nm, and a thickness direction retardation of 250 nm or less, especially 220 nm or less. 30 to 200 nm. In the birefringent layer A in which the in-plane retardation exceeds 20 nm or the birefringent layer A in which the thickness direction retardation exceeds 300 nm, the controllability of the slow axis change described above is poor, and the viewing angle range has a wide viewing power. Become scarce.
[0019]
The preferred birefringent layer B from the point of view of viewing angle range expansion of good visibility is plane retardation 60～190Nm, inter alia 80～170Nm, in particular 100 to 140 nm, _{N z} is 3.3 or less, especially 3. 0 or less, especially 2.8 or less. If the in-plane phase difference is less than 50 nm, the compensation effect for the change in viewing angle may be poor, and if it exceeds 200 nm, a color change such as coloring may occur due to the wavelength dispersion of the birefringence difference. In the value N _z exceeds 0.8 below and 3.5, the viewing angle range that can be compensated for changes in the slow axis depending on the viewing angle increases becomes narrow, wide viewing angle difficult.
[0020]
The arrangement order of the birefringent layers A and B with respect to the polarizing layer is arbitrary, but from the viewpoint of thinning the wide-field polarizing plate to be obtained, the polarizing layer 1 has the birefringent layer A31 as the polarizing layer side as shown in the figure. What used also as the transparent protective layer is preferable. In that case, a triacetyl cellulose film is particularly preferably used for forming the birefringent layer A in view of retardation characteristics and the like. The thicknesses of the birefringent layers A and B can be appropriately determined according to the target retardation characteristics and the like because they are related to the in-plane retardation as described above, but generally 5 to 500 μm, especially 10 to 350 μm, In particular, the thickness is set to 20 to 200 μm.
[0021]
The wide-field polarizing plate of the present invention can be preferably used for compensation of viewing angle characteristics due to birefringence of a liquid crystal cell, but the birefringent layers A and B and a polarizing layer are sequentially laminated separately in the manufacturing process of the liquid crystal display device. It can be carried out by an appropriate method such as a method or a method using a bilayer or three-layer laminate composed of an appropriate combination of a birefringent layer A, a birefringent layer B and a polarizing layer in advance. The latter pre-lamination method has advantages such as excellent quality stability and laminating workability, and can improve the manufacturing efficiency of the liquid crystal display device.
[0022]
When the birefringent layer B is laminated on one side of the polarizing layer, the transmission axis of the polarizing layer and the slow axis of the birefringent layer B are parallel or orthogonal to each other. Or, the orthogonal relationship is not limited to a parallel or orthogonal state in a strict sense, and an arrangement error in work is allowed. In addition, when there are variations in the direction of the transmission axis and the slow axis, they are arranged in a parallel relationship or an orthogonal relationship based on the average direction as a whole.
[0023]
In the above, when laminating the polarizing layer and the birefringent layers A and B, they can be fixed via an adhesive or the like, if necessary. It is preferable to fix by adhesion from the standpoint of preventing axial misalignment. For the adhesion, for example, an appropriate adhesive such as a transparent pressure sensitive adhesive such as acrylic, silicone, polyester, polyurethane, polyether or rubber can be used, and the type is not particularly limited. Absent. From the standpoint of preventing changes in optical properties, those that do not require a high-temperature process during curing and drying are preferred, and those that do not require a long curing process or drying time are desirable. Moreover, the thing which does not produce peeling etc. on heating or humidification conditions is preferable.
[0024]
In view of this, the weight average molecular weight of the monomer such as butyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate or (meth) acrylic acid is 100,000 or more, and the glass transition temperature is An acrylic pressure-sensitive adhesive composed of an acrylic polymer at 0 ° C. or lower can be particularly preferably used. An acrylic pressure-sensitive adhesive is more preferable than the point excellent in transparency, weather resistance, heat resistance and the like. In addition, when laminating | stacking what has a different refractive index, the adhesive agent etc. which have an intermediate | middle refractive index from points, such as suppression of reflection loss, are used preferably.
[0025]
Adhesives may be appropriately selected from fillers and pigments made of natural and synthetic resins, glass fibers and glass beads, metal powders and other inorganic powders, colorants, and antioxidants as necessary. Additives can also be blended. Moreover, it can also be set as the adhesive layer which contains microparticles | fine-particles and shows light diffusibility.
[0026]
Note that each of the polarizing layer, the birefringent layers A and B, the transparent protective layer, the adhesive layer, and the like includes, for example, a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, and a nickel complex compound. It is also possible to provide ultraviolet absorbing ability by a method of treating with an ultraviolet absorber such as.
[0027]
Formation of a liquid crystal display device using the wide-field polarizing plate of the present invention can be performed according to conventional methods. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing layer, a birefringent layer for the purpose of optical compensation, and an illumination system as necessary, and incorporating a drive circuit. However, in the present invention, there is no particular limitation except that the wide-field polarizing plate is provided on at least one side of the liquid crystal cell, and the conventional method can be applied.
[0028]
Accordingly, it is possible to form an appropriate liquid crystal display device such as a liquid crystal display device in which a wide-field polarizing plate is disposed on one side or both sides of a liquid crystal cell, or a backlight or reflector using an illumination system. In that case, the birefringent layers A and B are preferably disposed between the liquid crystal cell and the polarizing layer, particularly between the polarizing layer on the viewing side, from the viewpoint of the compensation effect. In practical use of the wide-field polarizing plate, it can be used in an appropriate form such as a laminate with other optical elements for forming a liquid crystal display device.
[0029]
3 and 4 show configuration examples of a liquid crystal display device using a wide-field polarizing plate. 4 is a liquid crystal cell, 5 is a backlight system, and 6 is a reflective layer. Reference numeral 7 denotes a light diffusion plate. The thing of FIG. 3 is a thing of the backlight type illumination system which has arrange | positioned the wide-field polarizing plate on both sides, and the thing of FIG. 4 is a thing of the reflection type illumination system which has arrange | positioned the wide-field polarizing plate only to one side.
[0030]
In the above, the forming component of the liquid crystal display device may be in a laminated integrated state or in an appropriate separated state. In forming the liquid crystal display device, appropriate optical elements such as a diffusion plate, an antiglare layer, an antireflection film, a protective layer and a protective plate can be appropriately disposed. The wide-field polarizing plate of the present invention can be preferably used in various display devices such as TFT type and MIM type using liquid crystal cells exhibiting birefringence such as TN type and STN type.
[0031]
【Example】
Example 1
A polarizing film obtained by stretching a 80 μm-thick polyvinyl alcohol film 5 times in an aqueous iodine solution and then drying it on one side of a triacetylcellulose film through a 15 μm-thick polyvinyl alcohol adhesive layer. Δnd: 6 nm (N _z : 10) made of an axially stretched product, a birefringent film A having a thickness direction retardation of 60 nm is adhered, and a 20 μm thick acrylic adhesive layer is formed thereon to provide a thickness of 60 μm. A birefringent film B of Δnd: 115 nm and N _z : 1.0 obtained by passing the polycarbonate film of 1.0 at a temperature of 160 ° C. between rolls having different peripheral speeds and stretching the film by 1.08 times was adhered. Wide-field polarizing plate was obtained. The adhesion treatment was performed so that the transmission axis of the polarizing film and the slow axis of the birefringent film B were in a parallel relationship.
[0032]
Example 2
Example 1 except that a birefringent film B having a Δnd of 80 nm and N _{z of} 2.0 obtained by biaxially stretching a polycarbonate film having a thickness of 60 μm in an atmosphere of 160 ° C. was used. Accordingly, a wide-field polarizing plate was obtained.
[0033]
Comparative Example 1
Only the polarizing film obtained according to Example 1 was used.
[0034]
Comparative Example 2
A polarizing plate was obtained in the same manner as in Example 1 except that the acrylic adhesive layer and the birefringent film B were not provided outside the birefringent film A.
[0035]
Comparative Example 3
A polarizing plate was obtained according to Example 1 except that the polarizing film and the birefringent film B were directly bonded via an acrylic adhesive layer without using the birefringent film A.
[0036]
Comparative Example 4
As a birefringent film B, a polycarbonate film having a thickness of 60 μm was passed through rolls having different peripheral speeds in an atmosphere at 160 ° C. and stretched 1.15 times. Δnd: 350 nm, N _z : 1. A polarizing plate was obtained in the same manner as in Example 1 except that 0 was used.
[0037]
Comparative Example 5
As a birefringent film B, a polycarbonate film having a thickness of 60 μm was passed through rolls having different peripheral speeds in an atmosphere of 160 ° C. and stretched 1.03 times. Δnd: 40 nm, N _z : 1. A polarizing plate was obtained in the same manner as in Example 1 except that 0 was used.
[0038]
Comparative Example 6
Example 1 except that a birefringent film A having a thickness of .DELTA.nd of 20 nm and a thickness direction retardation of 350 nm was obtained by biaxially stretching a polycarbonate film having a thickness of 60 .mu.m in an atmosphere of 160.degree. Accordingly, a polarizing plate was obtained.
[0039]
The polarizing plate obtained in the evaluation test example and the comparative example (wide field of view) is arranged on both sides (front / rear) of the TFT type liquid crystal cell, and blackening (display blackening) and white blurring (display whitening) are caused. The viewing angle ranges in the left and right directions and the up and down direction showing good visual recognition without causing a decrease in contrast and gradation inversion were examined.
[0040]
The results are shown in the following table.

[0041]
From the table, it can be seen that the viewing angle range on the left and right is remarkably improved and the viewing angle range in the up and down direction is slightly improved, as compared with the comparative example 1 of the example and the polarizing film alone. From comparison with Comparative Examples 2 to 6, it can be seen that it is advantageous to enlarge the viewing angle range by superimposing layers satisfying predetermined birefringence characteristics. In addition, the visual defect in the example and the comparative example 1 is due to the inversion of gradation.
[Brief description of the drawings]
1 is a partial cross-sectional perspective view of an example of a wide-field polarizing plate. FIG. 2 is a partial cross-sectional perspective view of another example of a wide-field polarizing plate. FIG. 3 is a cross-sectional view of an example of a liquid crystal display device. Example cross section [Explanation of symbols]
1: Polarizing layer 2: Adhesive layer 3: Superposed birefringent layer 31: Birefringent layer A
32: Birefringent layer B
4: Liquid crystal cell

Claims

On one side of the polarizing layer, assuming that the refractive index in the slow axis direction is n _s , the refractive index in the fast axis direction is n _f , the refractive index in the thickness direction is _nz , and the layer thickness is d, the formula: ( _ns − n _z) thickness retardation defined by d is at 300nm following _formula: (n s _-n f) and the birefringent layer a plane retardation following 20nm defined by d, the plane position phase difference is at 50 to 200 nm, _{_{_{wherein: (n s -n z) /}}} (n s -n f) n z defined by having a birefringent layer B of 0.8 to 3.5, and that A wide-field polarizing plate, wherein the slow axis of the birefringent layer B and the transmission axis of the polarizing layer are in a parallel relationship or an orthogonal relationship.

The wide-field polarizing plate according to claim 1, wherein the birefringent layer A also serves as a transparent protective layer of the polarizing layer.

3. The wide-field polarizing plate according to claim 1, wherein a part or all of the birefringent layer A, the birefringent layer B, and the polarizing layer are made of a polymer film.

The wide-field polarizing plate according to claim 1, wherein the birefringent layer A is made of triacetyl cellulose.

5. A liquid crystal display device comprising the wide-field polarizing plate according to claim 1 on at least one side of a liquid crystal cell.