JP4814419B2 - Optical element, surface light source device, and liquid crystal display device - Google Patents

Optical element, surface light source device, and liquid crystal display device Download PDF

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Publication number
JP4814419B2
JP4814419B2 JP2000281382A JP2000281382A JP4814419B2 JP 4814419 B2 JP4814419 B2 JP 4814419B2 JP 2000281382 A JP2000281382 A JP 2000281382A JP 2000281382 A JP2000281382 A JP 2000281382A JP 4814419 B2 JP4814419 B2 JP 4814419B2
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light source
optical element
liquid crystal
surface light
cholesteric liquid
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JP2002090535A (en
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直樹 高橋
忠幸 亀山
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Nitto Denko Corp
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Nitto Denko Corp
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Description

【0001】
【発明の技術分野】
本発明は、正面指向性よく発光する面光源装置や輝度に優れる液晶表示装置を形成しうるリオフィルター型の光学素子に関する。
【0002】
【発明の背景】
従来、サイドライト型導光板等の面光源による発散光の正面指向性を高めて正面輝度の向上を図りうる光学素子としては、プリズムシートが知られていた(特開平10−68804号公報、特開平10−82902号公報)。プリズムシートは、透明基材上に山形のプリズム形態をアレイしたものでそのプリズム形態を介し斜め方向の光を屈折させて面光源の正面(垂直)方向に向けその正面指向性を高めるものである。2枚以上のプリズムシートをそのプリズムのアレイ方向が交差するように重畳して多方向に発散する光を正面方向に集光する方式も知られている。しかしながらプリズムシートは、そのプリズム形態が接触等で傷付きやすくその傷付きは輝点や暗点の発生原因となるため面光源装置の組立時等に注意を要して取扱い難く作業性に乏しい問題点があった。また実用時にプリズムシートがフィルム等の隣接部材と密着するとプリズム機能が低下して性能低下を生じやすい問題点もあった。
【0003】
一方、液晶表示装置等の高輝度化を図る手段としては、面光源上にグランジャン配向のコレステリック液晶層と1/4波長板からなる光学素子を配置する方式も知られていた。この方式は、前記コレステリック液晶層が示す入射自然光を反射光と透過光として左右の円偏光に分離する性質を利用して、面光源による出射光を円偏光化しそれを1/4波長板を介し直線偏光化して偏光板に供給することにより偏光板による吸収ロスを抑制して輝度を向上させるようにしたものである。従って面光源による発散光の正面指向性の向上には寄与しない。
【0004】
【発明の技術的課題】
本発明は、隣接部材との密着による性能低下や形態の損傷を生じにくくて取扱作業性に優れると共に、正面指向性よく発光する面光源装置や輝度に優れる液晶表示装置を形成しうる光学素子の開発を課題とする。
【0005】
【課題の解決手段】
本発明は、三波長管からなる蛍光灯を光源とするサイドライト型又は直下型の面光源上に光学素子が配置された面光源装置であって、前記光学素子において、グランジャン配向のコレステリック液晶層が、円偏光の選択反射波長域が同じ可視光帯域となり、かつ選択反射される円偏光の左右が逆転する組合せで積層され、又は当該コレステリック液晶層が、円偏光の選択反射波長域が同じ可視光帯域となり、かつ選択反射される円偏光の左右が同じとなる組合せで1/2波長板を介し積層されており、前記選択反射波長域の短波長側の端の波長は、前記蛍光灯の輝線の波長λ(nm)よりもλ(nm)長く、λ≧10であり、前記面光源から前記光学素子に入射する前記波長λの可視光を、θ未満の入射角で入射したときには透過させ、θ以上の入射角で入射したときには遮光することを特徴とする面光源装置、及びその面光源装置に用いられることを特徴とする光学素子、並びに前記の面光源装置を用いてなることを特徴とする液晶表示装置を提供するものである
【0006】
【発明の効果】
本発明によればグランジャン配向のコレステリック液晶層による特定波長域の左右一方の円偏光を選択的に反射しかつ他の光は透過させる特性、及びその左右の円偏光に対する組合せに基づいて、前記特定波長域の光を選択反射して実質的に遮光することができる。なお前記左右の円偏光に対する組合せは、選択反射される円偏光の左右が逆転する組合せに加えて、その円偏光の左右が同じとなる組合せであっても1/2波長板を介在させることで円偏光の左右を逆転させることができてその目的を達成することができる。
【0007】
また前記の場合にコレステリック液晶層では入射角θに応じcosθの関係で選択反射の波長域が短波長側にシフトする特性を示すことから、コレステリック液晶層の選択反射波長域を制御することで正面方向(入射角0度)では前記波長λの可視光が透過し、その可視光がθ以上の入射角で入射したときには前記の遮光効果を生じさせて正面と入射角が一定値以内の方向の光のみが透過するものとすることができる。
【0008】
従って前記の入射角θが所定値以上の入射光に対して遮光効果を示す光学素子と、その遮光効果を生じる波長の可視光で発光する面光源を組合せることにより正面指向性よく発光する面光源装置を形成でき、それを用いて輝度に優れる液晶表示装置を形成することができる。また本発明による光学素子は、隣接部材と密着しても性能低下を生じず、また突起等の損傷を生じやすい形態を有しないので取扱作業性にも優れている。
【0009】
【発明の実施形態】
本発明による光学素子は、グランジャン配向のコレステリック液晶層を、円偏光の選択反射波長域が同じ可視光帯域となり、かつ選択反射される円偏光の左右が逆転する組合せで積層したもの、又は当該コレステリック液晶層を円偏光の選択反射波長域が同じ可視光帯域となり、かつ選択反射される円偏光の左右が同じとなる組合せで1/2波長板を介し積層したものよりなる。その例を図1、図2に示した。1、2がコレステリック液晶層、6が1/2波長板である。また3は粘着層、4は二色性偏光板、5は位相差板である。
【0010】
グランジャン配向のコレステリック液晶層は、その螺旋ピッチPに基づき式:λ=n・P・cosθにて算出される円偏光をブラッグ反射により選択的に反射し他の光は透過する(ただし、λは反射光の中心波長、nはコレステリック液晶分子の平均屈折率(n=(ne+no)/2)、θは光の入射角である)。反射される円偏光の左右は、グランジャン配向のコレステリック液晶層における螺旋方向の左右で決定される。また選択反射波長域△λは、液晶の屈折率差△nにより式:△λ=△n・P・cosθに基づいて中心波長λの近傍に形成される。
【0011】
本発明においてグランジャン配向のコレステリック液晶層は、図1の例の如く円偏光の選択反射波長域が同じ可視光帯域となりかつ選択反射される円偏光の左右が逆転する組合せ(1、2)、又は図2の例の如く円偏光の選択反射波長域が同じ可視光帯域となり、かつ選択反射される円偏光の左右が同じとなる組合せ(1)で用いられ、後者の円偏光の左右が同じとなる組合せでは1/2波長板6を介して積層される。これにより同じ選択反射波長域において左右いずれの円偏光も反射する光学素子が形成され、当該波長域の光の透過が阻止される。なお前記後者の場合には1/2波長板が先のコレステリック液晶層を透過した円偏光の左右を逆転させることに基づいて後のコレステリック液晶層で反射されることとなる。
【0012】
用いるグランジャン配向のコレステリック液晶層については、特に限定はなく上記した特性を示す適宜なものを用いうる。コレステリック液晶層は、単層物であってもよいし、グランジャン配向の螺旋ピッチが相違するもの、従って選択反射の波長域が相違するものの組合せにて2層又は3層以上を重畳した配置構造を有するものであってもよい。かかる重畳化にて選択反射の波長域を拡大することができる。
【0013】
前記した螺旋ピッチ相違のコレステリック液晶層の重畳に際し、螺旋ピッチの大小に基づく重畳の順序については特に限定はなく、任意な重畳順序とすることができる。一般には螺旋ピッチが大小の順序通りとなるように重畳することが光利用効率の向上、ひいては輝度向上の点より有利な場合が多い。
【0014】
なお上記した選択反射される円偏光の左右が逆転する組合せのコレステリック液晶層による光学素子を形成するときにも、前記した螺旋ピッチ相違のコレステリック液晶層の重畳方式を採りうるがその場合には、円偏光の左右が逆転するものの交互重畳方式や同じ円偏光方向のものの重畳一体化方式などの適宜な方式を採ることができ、螺旋ピッチの大小の順序を含めてその重畳方式に特に限定はない。
【0015】
グランジャン配向のコレステリック液晶層は、低分子液晶をセル基板で狭持したセル形態のものとして得ることもできるが、取扱性や薄型化等の点よりはフィルム状ないしシート状としたものが好ましく用いられる。フィルム状等のコレステリック液晶層は、例えば液晶ポリマーによるフィルム、透明基材上にラビング処理等による配向膜を介しグランジャン配向させた液晶ポリマーによる層を付設したもの、透明基材上に配向膜を介しグランジャン配向させた低分子液晶の紫外線硬化層を付設したものなどとして得ることができる。またコレステリック液晶層の重畳層は、重ね塗り方式や別途形生物の融着方式などにより形成することができる。なお螺旋方向が逆巻きのコレステリック液晶層(円偏光の左右が逆転)の重畳層は、別途形生物を粘着層等の透明接着層を介して行うことができる。
【0016】
前記の透明基材を形成する材料については特に限定はないが一般にはポリマーが用いられる。そのポリマーの例としては、二酢酸セルロースや三酢酸セルロースの如きセルロース系ポリマー、ポリエチレンテレフタレートやポリエチレンナフタレートの如きポリエステル系ポリマー、ポリカーボネート系ポリマーやポリメチルメタクリレートの如きアクリル系ポリマー、ポリスチレンやアクリロニトリル・スチレン共重合体の如きスチレン系ポリマー、ポリエチレンやポリプロピレン、シクロ系ないしノルボルネン構造を有するポリオレフィンやエチレン・プロピレン共重合体の如きオレフィン系ポリマー、塩化ビニル系ポリマー、ナイロンや芳香族ポリアミドの如きアミド系ポリマーがあげられる。
【0017】
またイミド系ポリマーやスルホン系ポリマー、ポリエーテルスルホン系ポリマーやポリエーテルエーテルケトン系ポリマー、ポリフェニレンスルフィド系ポリマーやビニルアルコール系ポリマー、塩化ビニリデン系ポリマーやビニルブチラール系ポリマー、アリレート系ポリマーやポリオキシメチレン系ポリマー、エポキシ系ポリマーや前記ポリマーのブレンド物、あるいはポリエステル系やアクリル系、ウレタン系やアミド系、シリコーン系やエポキシ系等の熱や紫外線照射等で硬化するポリマーなども前記透明基材の形成に用いうる。就中セルロース系フィルムの如く等方性に優れる、ないし複屈折の少ない透明基材が好ましく用いられる。
【0018】
図2の例の如く上記したコレステリック液晶層1を選択反射される円偏光の左右が同じとなる組合せで用いて1/2波長板6を介し積層して、透過円偏光の左右を逆転させるための1/2波長板としては、各種ポリマーの延伸フィルム等からなる複屈折性フィルム、ディスコチック系やネマチック系の如き液晶ポリマーの配向フィルム、その配向液晶層を透明基材上に支持したものなどの従来に準じた適宜なものを用いうる。
【0019】
前記の複屈折性フィルムを形成するポリマーは、上記した透明基材で例示したものなどの適宜なものであってよい。就中、例えばポリエステル系ポリマーやポリエーテルエーテルケトンの如く結晶性に優れるポリマーが好ましく用いうる。延伸フィルムは一軸や二軸等の適宜な方式で処理したものであってよい。また熱収縮性フィルムとの接着下に収縮力又は/及び延伸力を付与する方式などによりフィルムの厚さ方向の屈折率を制御した複屈折性フィルムなどであってもよい。さらに1/2波長板は、例えば位相差相違の位相差板を光軸を交差させて積層したものの如く、1/2波長板として機能する波長域を拡大したものであってもよい。
【0020】
図1の例の如く光学素子は、必要に応じ最外層のコレステリック液晶層の外側に粘着層3を介して二色性偏光板4や、さらにはその二色性偏光板を有する側に粘着層3を介して1層又は2層以上の位相差板を接着した形態で実用に供することもできる。斯かる二色性偏光板等との一体化は取扱作業性がより向上し、また面光源装置や液晶表示装置等の組立工程を簡易化することができる。
【0021】
前記の二色性偏光板は、液晶表示等を達成するための直線偏光を得ることを目的とするものである。その偏光板には所定偏光軸の直線偏光を透過して他の光は吸収する適宜なものを用いることができその種類について特に限定はない。一般には偏光フィルムやその片面又は両面を透明保護層で保護したものなどが用いられる。ちなみにその偏光フィルムの例としては、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処理したものなどがあげられる。
【0022】
また偏光フィルムの片面又は両面に必要に応じて設ける透明保護層は、上記の透明基材で例示したポリマーなどにて形成することができる。就中、透明性や機械的強度、熱安定性や水分遮蔽性等に優れるポリマーからなる透明保護層が好ましい。透明保護層は、ポリマー液の塗布方式やフィルムとしたものの接着積層方式などの適宜な方式で形成することができる。
【0023】
一方、上記した必要に応じての位相差板は、液晶セルの複屈折による位相差を補償して表示品位の向上を図ることなどを目的とするものである。かかる光学補償用の位相差板は通例、表示品位の向上の点より二色性偏光板と液晶セルの間に位置するように配置することが好ましい。光学補償用の位相差板としては、上記の1/2波長板に準じた複屈折性フィルムや配向液晶層などからなる適宜な位相差を有するものが用いられ、位相差等の光学特性の制御を目的に2層以上の位相差層を積層したものであってもよい。
【0024】
また前記の位相差板は、コレステリック液晶層より出射される透過円偏光を直線偏光化するための1/4波長板であってもよい。その場合、1/4波長板からなる位相差板は通例、コレステリック液晶層と二色性偏光板の間に配置される。1/4波長板を介し直線偏光化した光をその振動面が二色性偏光板の透過軸と可及的に一致するように供給することで吸収ロスを防止して輝度をより高めることができる。前記の1/4波長板は、1/2波長板と重畳する方式などで1/4波長板として機能する波長域の拡大を図ったものなどであってもよい。
【0025】
光学素子を形成するコレステリック液晶層や1/2波長板、必要に応じての二色性偏光板や位相差板等の各素材は単に重ね置いたものであってもよいが、光軸のズレ防止による品質の安定化や液晶表示装置の組立効率の向上などの点より粘着層等の透明接着層を介して積層一体化されていることが好ましい。ちなみに図例では、コレステリック液晶層の1と2や1/2波長板6、二色性偏光板4や位相差板5がそれぞれ粘着層3を介して接着一体化されている。
【0026】
粘着層は、例えばアクリル系重合体やシリコーン系ポリマー、ポリエステルやポリウレタン、ポリエーテルや合成ゴムなどの適宜なポリマーをベースポリマーとする粘着剤などの適宜な粘着性物質を用いて形成することができる。就中アクリル系粘着剤の如く光学的透明性や耐候性、耐熱性等に優れて熱や湿度の影響で浮きや剥がれ等を生じにくいものが好ましく用いうる。
【0027】
ちなみに前記のアクリル系粘着剤の例としては、メチル基やエチル基やブチル基等の炭素数が20以下のアルキル基を有する(メタ)アクリル酸のアルキルエステルと、(メタ)アクリル酸や(メタ)アクリル酸ヒドロキシエチル等の改良成分からなるアクリル系モノマーを、ガラス転移温度が0℃以下となる組合せにて共重合してなる、重量平均分子量が10万以上のアクリル系重合体をベースポリマーとするものなどがあげられるが、これに限定されない。
【0028】
粘着層の形成は、例えばカレンダーロール法等による圧延方式、ドクターブレード法やグラビアロールコータ法等による塗工方式などの適宜な方式で粘着性物質をコレステリック液晶層等の形成素材に付設する方式、あるいはそれに準じてセパレータ上に粘着層を形成しそれをコレステリック液晶層等の形成素材に移着する方式などの適宜な方式で行うことができる。
【0029】
なお粘着層は、それに透明粒子を含有させる方式などにより光拡散型のものとして形成することもできる。その透明粒子には、例えばシリカやアルミナ、チタニアやジルコニア、酸化錫や酸化インジウム、酸化カドミウムや酸化アンチモン等からなる、導電性のこともある無機系粒子、架橋又は未架橋のポリマー等からなる有機系粒子などの適宜なものを1種又は2種以上用いうる。
【0030】
図2の例の如く光学素子の外表面には必要に応じ液晶セル等の他部材との接着を目的とした粘着層3を設けることもできる。その粘着層が表面に露出する場合には実用に供するまでの間、汚染防止等の保護を目的にその表面をセパレータなどで仮着カバーしておくこともできる。また光学素子の形成素材が表面に露出する場合にはその露出表面を表面保護フィルムにて接着カバーして傷付き等から保護することもできる。
【0031】
前記のセパレータや表面保護フィルムは、光学素子の実用段階では剥離除去されその際に静電気やそれによるゴミ付着が生じる場合があるので必要に応じて帯電防止処理したセパレータや表面保護フィルムを用いることができる。また同様に例えば帯電防止層を光学素子の形成素材の層間や表面に位置させる方式などの適宜な方式で帯電防止処理した光学素子とすることもできる。
【0032】
光学素子は、各種の用途に用いることができ特に正面指向性の向上を目的とした面光源装置や輝度の向上を目的とした液晶表示装置の形成に好ましく用いうる。面光源装置は、例えば三波長管よりなる蛍光灯を光源とするサイドライト型や直下型等の面光源上に光学素子を配置する方式などにより形成することができる。また液晶表示装置は、例えば前記の面光源装置における光学素子の上側に必要に応じ偏光板等を介して適宜な液晶セルを配置する方式などにより形成することができる。その場合、光学素子が二色性偏光板を有するときにはそれを有しないコレステリック液晶層側が面光源側となるように配置される。
【0033】
前記において例えば波長約440nm、約550nm及び約610nmに輝線を示す三波長管よりなる汎用な蛍光灯(冷陰極管)を光源とする面光源を用いる場合、正面指向性に優れる面光源装置を得る点より好ましく用いうる光学素子は、円偏光の選択反射波長域が550〜610nmの範囲内にあるコレステリック液晶層と、当該波長域が610nm以上、就中その短波長端が610〜630nm程度で長波長端が大きいもの、従って当該波長域の短波長端が少なくとも610nmでその波長域が可及的に大きいもの、実用的には当該波長域が610〜800nmの範囲内にあるコレステリック液晶層との2種以上(円偏光の左右を逆転させる関係のコレステリック液晶層では合計4種以上)、特にそれらと当該波長域が440〜550nmの範囲内にあるコレステリック液晶層との3種以上(円偏光の左右を逆転させる関係のコレステリック液晶層では合計6種以上)を用いて前記3種の輝線に対応した選択反射波長域を示すものである。
【0034】
前記のように正面指向性に優れる面光源装置を得る点より好ましく用いうる光学素子は、三波長管による輝線に対応した選択反射波長域を示すものである。さらに入射角が20度超となる輝線を遮光し、入射角が20度以内の正面指向性に優れる輝線を透過させる点よりは、上記したcosθの関与による短波長側シフトに基づいて光源の各輝線よりも10nm以上、就中15〜100nm、特に20〜50nm長い波長を選択反射波長域の短波長側の端とするコレステリック液晶層を用いた光学素子が好ましく用いられる。
【0035】
上記において光学素子で遮光されて面光源側に反射された光は光反射層を介して閉じ込めることができる。従ってその場合には、面光源の発光を遮ることなく光反射層を設けうるサイドライト型導光板等による面光源の使用が好ましい。導光板等の底面に光反射層を設けて前記遮光による反射光を光学素子と光反射層の間に閉じ込めることにより、その間に介在する導光板等による屈折や拡散ないし散乱等による光路変更で光学素子を透過しうる入射角の小さい光となり、それにより光学素子を正面指向性よく透過して輝度の向上を図ることができる。
【0036】
面光源装置や液晶表示装置の形成に際して光学素子は、面光源の発光面や液晶セルの視認面又は/及び背面等の適宜な位置に単に設置するだけであってもよいが、他部材とのスティッキングや耐熱性等の性能試験時などにおけるカール、ウネリの発生を防止する点などより粘着層等の透明接着層を介して面光源や液晶セル等に接着処理することが好ましい。なお面光源装置や液晶表示装置の形成に際しては、防眩層や反射防止層、光拡散層などの適宜な光学層の1層又は2層以上を適宜な位置に配置することができる。
【0037】
【実施例】
実施例1
厚さ80μmの三酢酸セルロースフィルムの上にラビング配向膜を介しコレステリック液晶ポリマーを塗布し配向処理して選択反射波長域が570〜605nmの左円偏光反射型及び右円偏光反射型のコレステリック液晶層を形成し、それらを厚さ20μmのアクリル系粘着層を介し接着して光学素子を得た。
【0038】
実施例2
ポリカーボネートからなる1/2波長板の両側に厚さ20μmのアクリル系粘着層を介して実施例1に準じた右円偏光反射型のコレステリック液晶層を接着して光学素子を得た。
【0039】
実施例3
実施例1に準じ選択反射波長域が460〜489nm、570〜603nm又は630nm〜670nmの左円偏光反射型及び右円偏光反射型のコレステリック液晶層を形成し、それらをアクリル系粘着層を介し接着積層して光学素子を得た。
【0040】
比較例
頂角が90℃の市販プリズムシートを光学素子として用いた。
【0041】
評価試験
導光板の側面に輝線波長が438nmと545nmと610nmの三波長管よりなる蛍光灯を配置してなるサイドライト型面光源の発光面に光拡散シートを介し実施例、比較例で得た光学素子を載置して面光源装置を形成し輝度計(トプコン社製、BM7)にてその光学素子上の正面輝度を調べた。
【0042】
前記の結果を次表に示した。

Figure 0004814419

【図面の簡単な説明】
【図1】実施例の断面図
【図2】他の実施例の断面図
【符号の説明】
1、2:コレステリック液晶層
3:粘着層
4:二色性偏光板
5:位相差板
6:1/2波長板[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rio filter type optical element that can form a surface light source device that emits light with good front directivity and a liquid crystal display device that is excellent in luminance.
[0002]
BACKGROUND OF THE INVENTION
Conventionally, a prism sheet has been known as an optical element capable of improving the front luminance of diverging light by a surface light source such as a sidelight type light guide plate and improving the front luminance (Japanese Patent Laid-Open No. 10-68804, Japanese Patent Application Laid-Open No. 10-68804). (Kaihei 10-82902). The prism sheet is an array of mountain-shaped prisms on a transparent base material, and refracts light in an oblique direction through the prisms to enhance the front directivity toward the front (vertical) direction of the surface light source. . There is also known a method in which two or more prism sheets are superimposed so that the array directions of the prisms intersect to collect light diverging in multiple directions in the front direction. However, the prism sheet is easily damaged by contact, etc., and the damage can cause bright spots and dark spots, so it is difficult to handle and work with care when assembling the surface light source device. There was a point. Further, when the prism sheet is brought into close contact with an adjacent member such as a film in practical use, there is a problem in that the prism function is lowered and the performance is likely to be deteriorated.
[0003]
On the other hand, as means for increasing the brightness of a liquid crystal display device or the like, a system in which an optical element composed of a cholesteric liquid crystal layer with a Grandjean orientation and a quarter wave plate is arranged on a surface light source has been known. This method utilizes the property of separating the incident natural light shown by the cholesteric liquid crystal layer into right and left circularly polarized light as reflected light and transmitted light, and circularly polarizes the outgoing light from the surface light source through a quarter-wave plate. By making it linearly polarized and supplying it to the polarizing plate, the absorption loss due to the polarizing plate is suppressed and the luminance is improved. Therefore, it does not contribute to the improvement of the front directivity of the divergent light from the surface light source.
[0004]
[Technical Problem of the Invention]
The present invention is an optical element that can form a surface light source device that emits light with good front directivity and a liquid crystal display device that is excellent in luminance while being less likely to cause performance degradation and form damage due to close contact with adjacent members. Development is an issue.
[0005]
[Means for solving problems]
The present invention relates to a side light type or a direct-type surface light source device optical elements are arranged on the surface light source as a light source a fluorescent lamp comprising a three-band tube, wherein the optical element, grayed Ranjan orientation of the cholesteric liquid crystal The layers are stacked in a combination in which the selective reflection wavelength region of circularly polarized light has the same visible light band and the circularly polarized light that is selectively reflected is reversed, or the cholesteric liquid crystal layer has the same selective reflection wavelength region of circularly polarized light. The circularly polarized light that is in the visible light band and is selectively reflected is laminated through a half-wave plate in the same combination, and the wavelength at the short wavelength side end of the selective reflection wavelength region is the fluorescent lamp Λ 2 (nm) longer than the wavelength λ 1 (nm) of the emission line, λ 2 ≧ 10, and visible light having the wavelength λ 1 incident on the optical element from the surface light source is incident at an incident angle of less than θ. Transmitted when incident A surface light source device that shields light when incident at an incident angle of θ or more, an optical element that is used in the surface light source device, and the surface light source device. The present invention provides a liquid crystal display device .
[0006]
【The invention's effect】
According to the present invention, based on the characteristic of selectively reflecting the left and right circularly polarized light in a specific wavelength region and transmitting the other light by the Grandjean-oriented cholesteric liquid crystal layer, and the combination with respect to the left and right circularly polarized light, Light in a specific wavelength range can be selectively reflected and substantially blocked. In addition to the combination in which the left and right circularly polarized light that is selectively reflected is reversed, the combination with respect to the left and right circularly polarized light can be obtained by interposing a half-wave plate even if the left and right circularly polarized light is the same combination. The left and right of circularly polarized light can be reversed to achieve its purpose.
[0007]
In the above case, the cholesteric liquid crystal layer has a characteristic that the wavelength range of selective reflection shifts to the short wavelength side according to the relationship of cos θ according to the incident angle θ. In the direction (incidence angle 0 degree), the visible light having the wavelength λ 1 is transmitted, and when the visible light is incident at an incident angle of θ or more, the light shielding effect is produced, and the front and the incident angle are within a certain value. It is possible to transmit only the light.
[0008]
Accordingly, a surface that emits light with good front directivity by combining an optical element that exhibits a light shielding effect with respect to incident light having an incident angle θ of a predetermined value or more and a surface light source that emits visible light having a wavelength that produces the light shielding effect. A light source device can be formed, and a liquid crystal display device having excellent luminance can be formed using the light source device. Further, the optical element according to the present invention does not deteriorate in performance even if it is in close contact with an adjacent member, and is excellent in handling workability because it does not have a form in which protrusions and the like are easily damaged.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The optical element according to the present invention is a laminate in which a cholesteric liquid crystal layer having a Grandian orientation is laminated in a combination in which the selective reflection wavelength region of circularly polarized light is the same visible light band and the left and right of selectively circularly polarized light are reversed, or A cholesteric liquid crystal layer is formed by laminating a cholesteric liquid crystal layer through a half-wave plate in such a combination that the selective reflection wavelength region of circularly polarized light is the same visible light band and the left and right of selectively circularly polarized light are the same. Examples thereof are shown in FIGS. 1 and 2 are cholesteric liquid crystal layers, and 6 is a half-wave plate. 3 is an adhesive layer, 4 is a dichroic polarizing plate, and 5 is a retardation plate.
[0010]
Based on the helical pitch P, the Grandjean-oriented cholesteric liquid crystal layer selectively reflects circularly polarized light calculated by the formula: λ = n · P · cos θ by Bragg reflection and transmits other light (provided that λ Is the central wavelength of the reflected light, n is the average refractive index of the cholesteric liquid crystal molecules (n = (ne + no) / 2), and θ is the incident angle of light). The left and right sides of the circularly polarized light reflected are determined by the left and right sides of the spiral direction of the cholesteric liquid crystal layer with the Grand Jean alignment. The selective reflection wavelength region Δλ is formed in the vicinity of the center wavelength λ based on the formula: Δλ = Δn · P · cos θ due to the refractive index difference Δn of the liquid crystal.
[0011]
In the present invention, the Grandjean-oriented cholesteric liquid crystal layer is a combination (1, 2) in which the selective reflection wavelength region of circularly polarized light is the same visible light band as shown in the example of FIG. Alternatively, as shown in FIG. 2, the circularly polarized light is used in the combination (1) in which the selective reflection wavelength region of the circularly polarized light is the same visible light band, and the left and right of the circularly polarized light that is selectively reflected is the same. In such a combination, they are stacked via the half-wave plate 6. As a result, an optical element that reflects both left and right circularly polarized light in the same selective reflection wavelength region is formed, and transmission of light in the wavelength region is blocked. In the latter case, the half-wave plate is reflected by the subsequent cholesteric liquid crystal layer based on reversing the left and right circularly polarized light transmitted through the previous cholesteric liquid crystal layer.
[0012]
There is no particular limitation on the Grande-aligned cholesteric liquid crystal layer to be used, and any suitable layer having the above-described characteristics can be used. The cholesteric liquid crystal layer may be a single layer, or an arrangement structure in which two layers or three or more layers are superposed in a combination of those having different helical pitches of Grandjean alignment, and hence different selective reflection wavelength regions. It may have. The wavelength range of selective reflection can be expanded by such superposition.
[0013]
When superimposing the cholesteric liquid crystal layers having different spiral pitches, there is no particular limitation on the order of superimposition based on the magnitude of the spiral pitch, and an arbitrary superposition order can be used. In general, it is often more advantageous to superimpose the spiral pitches in order of magnitude in order to improve the light utilization efficiency and hence the luminance.
[0014]
In addition, when forming an optical element with a cholesteric liquid crystal layer in which the left and right of circularly polarized light selectively reflected as described above are reversed, the above-described superposition method of cholesteric liquid crystal layers with different spiral pitches can be adopted. Appropriate methods such as an alternating superimposing method in which the left and right sides of circularly polarized light are reversed and a superposing and integrating method in the same circularly polarized direction can be adopted, and the superimposing method including the order of the spiral pitch is not particularly limited. .
[0015]
The Grande-aligned cholesteric liquid crystal layer can also be obtained as a cell having a low molecular liquid crystal sandwiched between cell substrates, but it is preferably in the form of a film or sheet from the standpoint of handling and thinning. Used. A cholesteric liquid crystal layer such as a film is, for example, a film made of a liquid crystal polymer, a layer made of a liquid crystal polymer that has been subjected to a Grandjean alignment through an alignment film formed by rubbing on a transparent substrate, and an alignment film on a transparent substrate. It can be obtained, for example, as a UV-cured layer of low-molecular liquid crystal with a Grandjean orientation. Further, the superposed layer of the cholesteric liquid crystal layer can be formed by an overcoating method or a separate fusion method. In addition, the superimposed layer of the cholesteric liquid crystal layer (the left and right of circularly polarized light are reversed) whose spiral direction is reversed can be separately formed through a transparent adhesive layer such as an adhesive layer.
[0016]
Although there is no limitation in particular about the material which forms the said transparent base material, generally a polymer is used. Examples of the polymer include cellulose polymers such as cellulose diacetate and cellulose triacetate, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, acrylic polymers such as polycarbonate polymers and polymethyl methacrylate, polystyrene, acrylonitrile and styrene. Styrenic polymers such as copolymers, polyethylene and polypropylene, polyolefins having cyclo or norbornene structures, olefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamides. can give.
[0017]
Also imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers Polymers, epoxy polymers, blends of the above-mentioned polymers, polymers such as polyesters, acrylics, urethanes, amides, silicones, epoxys, etc. that cure by heat or UV irradiation can also be used to form the transparent substrate. Can be used. In particular, a transparent substrate that is excellent in isotropy, such as a cellulose-based film, or that has little birefringence is preferably used.
[0018]
In order to reverse the left and right of the transmitted circularly polarized light by laminating the cholesteric liquid crystal layer 1 described above as a combination of circularly polarized light selectively reflected through the half-wave plate 6 using the same combination of the left and right circularly polarized light as shown in the example of FIG. The half-wave plate is a birefringent film composed of stretched films of various polymers, a liquid crystal polymer alignment film such as a discotic or nematic system, and a liquid crystal polymer alignment film supported on a transparent substrate. An appropriate one according to the conventional method can be used.
[0019]
The polymer forming the birefringent film may be an appropriate one such as those exemplified for the transparent substrate. Among them, polymers having excellent crystallinity such as polyester polymers and polyether ether ketones can be preferably used. The stretched film may be processed by an appropriate method such as uniaxial or biaxial. Moreover, the birefringent film etc. which controlled the refractive index of the thickness direction of the film by the system etc. which provide a shrinkage force or / and extending | stretching force under adhesion | attachment with a heat-shrinkable film may be sufficient. Further, the half-wave plate may be obtained by enlarging the wavelength region that functions as a half-wave plate, such as a laminate of retardation plates having different phase differences with the optical axes crossed.
[0020]
As shown in the example of FIG. 1, the optical element includes a dichroic polarizing plate 4 on the outer side of the outermost cholesteric liquid crystal layer as needed through an adhesive layer 3, and an adhesive layer on the side having the dichroic polarizing plate. 3 can be put to practical use in a form in which one or two or more retardation plates are bonded together. Integration with such a dichroic polarizing plate improves handling workability, and can simplify the assembly process of a surface light source device, a liquid crystal display device, and the like.
[0021]
The dichroic polarizing plate is intended to obtain linearly polarized light for achieving liquid crystal display or the like. As the polarizing plate, an appropriate material that transmits linearly polarized light having a predetermined polarization axis and absorbs other light can be used, and the type thereof is not particularly limited. In general, a polarizing film or a film having one or both sides thereof protected with a transparent protective layer is used. Incidentally, as an example of the polarizing film, iodine and / or a dichroic dye are added to a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or an ethylene / vinyl acetate copolymer partially saponified film. For example, it may be drawn and stretched.
[0022]
Moreover, the transparent protective layer provided as needed on one side or both sides of a polarizing film can be formed with the polymer etc. which were illustrated by said transparent base material. In particular, a transparent protective layer made of a polymer excellent in transparency, mechanical strength, thermal stability, moisture shielding properties and the like is preferable. The transparent protective layer can be formed by an appropriate method such as a coating method of a polymer solution or an adhesive lamination method of a film.
[0023]
On the other hand, the above-described retardation plate is used for the purpose of improving the display quality by compensating for the phase difference due to the birefringence of the liquid crystal cell. Such a retardation plate for optical compensation is usually preferably disposed so as to be positioned between the dichroic polarizing plate and the liquid crystal cell in order to improve display quality. As the retardation plate for optical compensation, a plate having an appropriate retardation composed of a birefringent film or an alignment liquid crystal layer according to the above half-wave plate is used, and control of optical characteristics such as retardation is performed. For the purpose, two or more retardation layers may be laminated.
[0024]
The retardation plate may be a quarter wavelength plate for linearly polarizing the transmitted circularly polarized light emitted from the cholesteric liquid crystal layer. In that case, a retardation plate composed of a quarter-wave plate is usually disposed between the cholesteric liquid crystal layer and the dichroic polarizing plate. By supplying linearly polarized light through a quarter-wave plate so that its vibration surface coincides with the transmission axis of the dichroic polarizing plate as much as possible, absorption loss is prevented and luminance is further increased. it can. The quarter-wave plate may be one in which a wavelength range that functions as a quarter-wave plate is expanded by a method of overlapping with a half-wave plate or the like.
[0025]
Each material such as a cholesteric liquid crystal layer, a half-wave plate, and a dichroic polarizing plate and a retardation plate, which form an optical element, may be simply stacked, but the optical axis is shifted. In view of stabilization of quality by prevention and improvement of assembly efficiency of the liquid crystal display device, it is preferable that they are laminated and integrated through a transparent adhesive layer such as an adhesive layer. Incidentally, in the illustrated example, the cholesteric liquid crystal layers 1 and 2, the half-wave plate 6, the dichroic polarizing plate 4, and the retardation plate 5 are bonded and integrated through the adhesive layer 3.
[0026]
The adhesive layer can be formed using an appropriate adhesive material such as an adhesive having an appropriate polymer such as an acrylic polymer, silicone polymer, polyester, polyurethane, polyether, or synthetic rubber as a base polymer. . In particular, an acrylic pressure-sensitive adhesive having excellent optical transparency, weather resistance, heat resistance, and the like, which is less likely to float or peel off due to the influence of heat or humidity, can be preferably used.
[0027]
Incidentally, examples of the acrylic pressure-sensitive adhesive include alkyl esters of (meth) acrylic acid having an alkyl group having 20 or less carbon atoms such as methyl group, ethyl group and butyl group, and (meth) acrylic acid and (meth ) An acrylic polymer having a weight average molecular weight of 100,000 or more obtained by copolymerizing an acrylic monomer comprising an improved component such as hydroxyethyl acrylate with a combination having a glass transition temperature of 0 ° C. or less is defined as a base polymer. This is not limited to this.
[0028]
Formation of the adhesive layer is, for example, a method of attaching an adhesive substance to a forming material such as a cholesteric liquid crystal layer by an appropriate method such as a rolling method by a calendar roll method or the like, a coating method by a doctor blade method or a gravure roll coater method, Or according to it, it can carry out by suitable methods, such as a method of forming an adhesion layer on a separator and transferring it to formation materials, such as a cholesteric liquid crystal layer.
[0029]
The pressure-sensitive adhesive layer can also be formed as a light diffusion type by a method in which transparent particles are contained therein. Examples of the transparent particles include silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide, and the like. One type or two or more types of suitable particles such as system particles can be used.
[0030]
As in the example of FIG. 2, an adhesive layer 3 for the purpose of bonding to other members such as a liquid crystal cell can be provided on the outer surface of the optical element as necessary. When the adhesive layer is exposed on the surface, the surface can be temporarily covered with a separator or the like for the purpose of protection such as contamination prevention until practical use. When the optical element forming material is exposed on the surface, the exposed surface can be protected by being covered with a surface protective film.
[0031]
The separator and the surface protective film are peeled and removed at the practical stage of the optical element, and at that time, static electricity and dust may be attached thereto, so an antistatic treated separator or surface protective film may be used as necessary. it can. Similarly, an optical element that has been subjected to antistatic treatment by an appropriate method, such as a method in which an antistatic layer is positioned between layers or surfaces of the optical element forming material, can also be used.
[0032]
The optical element can be used for various applications, and can be preferably used for forming a surface light source device for improving the front directivity and a liquid crystal display device for improving the luminance. The surface light source device can be formed by, for example, a method of arranging an optical element on a surface light source such as a side light type or a direct type using a fluorescent lamp made of a three-wavelength tube as a light source. In addition, the liquid crystal display device can be formed, for example, by a method in which an appropriate liquid crystal cell is disposed on the upper side of the optical element in the surface light source device as necessary via a polarizing plate or the like. In that case, when an optical element has a dichroic polarizing plate, it arrange | positions so that the cholesteric liquid crystal layer side which does not have it may become a surface light source side.
[0033]
In the above, for example, when a surface light source using a general-purpose fluorescent lamp (cold cathode tube) composed of a three-wavelength tube having emission lines at wavelengths of about 440 nm, about 550 nm, and about 610 nm is used, a surface light source device having excellent front directivity is obtained. An optical element that can be used more preferably is a cholesteric liquid crystal layer having a selective reflection wavelength range of circularly polarized light in the range of 550 to 610 nm, a wavelength range of 610 nm or more, and particularly a short wavelength end of about 610 to 630 nm. A cholesteric liquid crystal layer having a large wavelength end, that is, a short wavelength end of at least 610 nm and a wavelength range that is as large as possible, and practically the wavelength range in the range of 610 to 800 nm. 2 or more types (4 or more types in total in the case of a cholesteric liquid crystal layer in which the right and left of circularly polarized light are reversed), especially those in which the wavelength range is in the range of 440 to 550 nm Rick 3 or more and the liquid crystal layer (in the circularly polarized light cholesteric liquid crystal layer of the relationship reversing the left and right total of six or more) shows the selective reflection wavelength region corresponding to the three emission lines used.
[0034]
As described above, an optical element that can be preferably used from the viewpoint of obtaining a surface light source device having excellent front directivity exhibits a selective reflection wavelength region corresponding to a bright line by a three-wavelength tube. Further, since the bright line having an incident angle of more than 20 degrees is shielded and the bright line having an incident angle of 20 degrees or less and having excellent front directivity is transmitted, each of the light sources is based on the short wavelength side shift due to the cos θ described above. An optical element using a cholesteric liquid crystal layer having a wavelength of 10 nm or more, especially 15 to 100 nm, particularly 20 to 50 nm longer than the bright line, at the short wavelength side end of the selective reflection wavelength region is preferably used.
[0035]
In the above, the light shielded by the optical element and reflected to the surface light source side can be confined via the light reflecting layer. Therefore, in that case, it is preferable to use a surface light source such as a side light type light guide plate that can be provided with a light reflection layer without blocking light emission of the surface light source. By providing a light reflection layer on the bottom surface of the light guide plate, etc., and confining the light reflected by the light shielding between the optical element and the light reflection layer, the optical path is changed by refraction, diffusion or scattering by the light guide plate interposed therebetween. Light having a small incident angle that can be transmitted through the element can be transmitted, whereby the optical element can be transmitted with good front directivity and luminance can be improved.
[0036]
In the formation of the surface light source device and the liquid crystal display device, the optical element may be simply installed at an appropriate position such as the light emitting surface of the surface light source or the viewing surface or / and the back surface of the liquid crystal cell. From the viewpoint of preventing the occurrence of curling and undulation during performance tests such as sticking and heat resistance, it is preferable to perform an adhesion treatment on a surface light source, a liquid crystal cell or the like via a transparent adhesive layer such as an adhesive layer. When forming a surface light source device or a liquid crystal display device, one or more of appropriate optical layers such as an antiglare layer, an antireflection layer, and a light diffusion layer can be disposed at appropriate positions.
[0037]
【Example】
Example 1
A cholesteric liquid crystal polymer is applied to a cellulose triacetate film having a thickness of 80 μm via a rubbing alignment film and subjected to an alignment treatment, and a cholesteric liquid crystal layer of a left circularly polarized reflection type and a right circularly polarized reflection type having a selective reflection wavelength range of 570 to 605 nm. Were bonded together via an acrylic adhesive layer having a thickness of 20 μm to obtain an optical element.
[0038]
Example 2
A right circularly polarized reflective cholesteric liquid crystal layer according to Example 1 was adhered to both sides of a polycarbonate half-wave plate via an acrylic adhesive layer having a thickness of 20 μm to obtain an optical element.
[0039]
Example 3
According to the first embodiment, left and right circularly polarized reflection type cholesteric liquid crystal layers having a selective reflection wavelength range of 460 to 489 nm, 570 to 603 nm, and 630 nm to 670 nm are formed, and these are bonded via an acrylic adhesive layer. An optical element was obtained by laminating.
[0040]
Comparative Example A commercially available prism sheet having an apex angle of 90 ° C. was used as an optical element.
[0041]
Evaluation test Obtained in Examples and Comparative Examples through a light diffusion sheet on the light emitting surface of a sidelight type surface light source in which fluorescent lamps composed of three-wavelength tubes with emission line wavelengths of 438 nm, 545 nm and 610 nm are arranged on the side surface of the light guide plate. An optical element was placed to form a surface light source device, and the front luminance on the optical element was examined with a luminance meter (Topcon, BM7).
[0042]
The results are shown in the following table.
Figure 0004814419

[Brief description of the drawings]
FIG. 1 is a sectional view of an embodiment. FIG. 2 is a sectional view of another embodiment.
1, 2: Cholesteric liquid crystal layer 3: Adhesive layer 4: Dichroic polarizing plate 5: Retardation plate 6: 1/2 wavelength plate

Claims (8)

三波長管からなる蛍光灯を光源とするサイドライト型又は直下型の面光源上に光学素子が配置された面光源装置であって、
前記光学素子において、グランジャン配向のコレステリック液晶層が、円偏光の選択反射波長域が同じ可視光帯域となり、かつ選択反射される円偏光の左右が逆転する組合せで積層されており、前記選択反射波長域の短波長側の端の波長は、前記蛍光灯の輝線の波長λ(nm)よりもλ(nm)長く、λ≧10であり、前記面光源から前記光学素子に入射する前記波長λの可視光を、θ未満の入射角で入射したときには透過させ、θ以上の入射角で入射したときには遮光することを特徴とする面光源装置
A surface light source device in which an optical element is disposed on a side light type or direct type surface light source using a fluorescent lamp made of a three-wavelength tube as a light source,
In the optical element, the cholesteric liquid crystal layer of the grayed Ranjan orientation, the selective reflection wavelength region of the circularly polarized light becomes the same visible light band, and has left and right of the circle is selected reflected polarized light are laminated in combination to reverse the selective reflection wavelength end of the short wavelength side of the wavelength range, the fluorescent lamp bright line wavelength lambda 1 (nm) than lambda 2 (nm) long and a lambda 2 ≧ 10, incident from the surface light source to the optical element the wavelength lambda 1 of the visible light, is transmitted through when incident at an incident angle of less than theta, surface light source device characterized by light blocking when incident at an incident angle greater than theta.
三波長管からなる蛍光灯を光源とするサイドライト型又は直下型の面光源上に光学素子が配置された面光源装置であって、
前記光学素子において、グランジャン配向のコレステリック液晶層が、円偏光の選択反射波長域が同じ可視光帯域となり、かつ選択反射される円偏光の左右が同じとなる組合せで1/2波長板を介して積層されており、前記選択反射波長域の短波長側の端の波長は、前記蛍光灯の輝線の波長λ(nm)よりもλ(nm)長く、λ≧10であり、前記面光源から前記光学素子に入射する前記波長λの可視光を、θ未満の入射角で入射したときには透過させ、θ以上の入射角で入射したときには遮光することを特徴とする面光源装置
A surface light source device in which an optical element is disposed on a side light type or direct type surface light source using a fluorescent lamp made of a three-wavelength tube as a light source,
In the optical element, the cholesteric liquid crystal layer of the grayed Ranjan orientation, become selective reflection wavelength region of the circularly polarized light is the same visible light band, and through the half-wave plate in combination right is the same selective reflection is the circularly polarized light The wavelength of the short wavelength side end of the selective reflection wavelength region is λ 2 (nm) longer than the wavelength λ 1 (nm) of the fluorescent lamp, and λ 2 ≧ 10, A surface light source device characterized in that visible light having a wavelength λ 1 incident on the optical element from a surface light source is transmitted when incident at an incident angle less than θ, and is shielded when incident at an incident angle greater than θ .
請求項1又は2において、前記光学素子は、円偏光の選択反射波長域が550〜610nmの範囲内にあるコレステリック液晶層と610〜800nmの範囲内にあるコレステリック液晶層、又はそれらと440〜550nmの範囲内にあるコレステリック液晶層を用いたものである面光源装置。  3. The optical element according to claim 1, wherein the optical element includes a cholesteric liquid crystal layer having a selective reflection wavelength range of circularly polarized light in a range of 550 to 610 nm and a cholesteric liquid crystal layer in a range of 610 to 800 nm, or 440 to 550 nm. A surface light source device using a cholesteric liquid crystal layer in the range. 請求項1から3のいずれか一項において、前記光学素子は、最外層のコレステリック液晶層の外側に粘着層を介して二色性偏光板が接着された光学素子である面光源装置。  4. The surface light source device according to claim 1, wherein the optical element is an optical element in which a dichroic polarizing plate is bonded to the outside of an outermost cholesteric liquid crystal layer via an adhesive layer. 5. 請求項4において、前記光学素子は、二色性偏光板を有する側に1層又は2層以上の位相差板が粘着層を介して接着された光学素子である面光源装置。  5. The surface light source device according to claim 4, wherein the optical element is an optical element in which one or two or more retardation plates are bonded to the side having a dichroic polarizing plate via an adhesive layer. ランジャン配向のコレステリック液晶層を、円偏光の選択反射波長域が同じ可視光帯域となり、かつ選択反射される円偏光の左右が逆転する組合せで積層してなり、請求項1および3から5のいずれか一項に記載の面光源装置に用いられることを特徴とする光学素子。The cholesteric liquid crystal layer of the grayed Ranjan orientation, become selective reflection wavelength region of the circularly polarized light is the same visible light band, and formed by laminating a combination of the left and right selection reflected by the circularly polarized light is reversed, claims 1 and 3 of 5 An optical element used in the surface light source device according to any one of the above items. ランジャン配向のコレステリック液晶層を、円偏光の選択反射波長域が同じ可視光帯域となり、かつ選択反射される円偏光の左右が同じとなる組合せで1/2波長板を介し積層してなり、請求項2から5のいずれか一項に記載の面光源装置に用いられることを特徴とする光学素子。The cholesteric liquid crystal layer of the grayed Ranjan orientation, the selective reflection wavelength region of the circularly polarized light becomes the same visible light band, and the left and right of the circle is selected reflective polarizing formed by laminating through the half-wave plate in combination of the same, An optical element used in the surface light source device according to claim 2. 請求項1から5のいずれか一項に記載の面光源装置を用いてなることを特徴とする液晶表示装置。  A liquid crystal display device comprising the surface light source device according to claim 1.
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