JP3811465B2 - Polarizing element, polarized light source, and image display apparatus using them - Google Patents

Description

【０１５３】
ポジティブＣプレート層作製の具体的な操作は以下の通りである。すなわち、まず、重合性ネマチックモノマーＡをシクロペンタンに溶解させ、溶質濃度が３０ｗｔ％となるように調整した。さらに、この溶液に１ｗｔ％の反応開始剤（チバガイギ製、Ｉｒｇ９０７（商品名））を添加して塗工用溶液とした。一方、ＰＥＴフィルム（東レ製、ルミラー（商品名）、厚み７５μｍ）を準備し、この上に離型処理剤（オクタデシルトリメトキシシラン）のシクロヘキサン溶液（０．１ｗｔ％）を薄く塗布し、乾燥させて垂直配向膜を形成して配向基板とした。そして、この配向基板の垂直配向膜形成面上に前記塗工用溶液をワイヤーバーで塗布した。この時の溶液塗布量は、乾燥後の厚みが２μｍとなるように調整した。これを９０℃で２分間乾燥させ、さらに液晶の等方性転移温度１３０℃まで一旦加熱後、徐冷して均一な配向状態を保持した。そして、８０℃で紫外線照射（１０ｍＷ／平方ｃｍ×１分）により硬化して、目的のポジティブＣプレート層が前記配向基板上に形成された積層体を得た。このポジティブＣプレートの位相差を測定した所、５５０ｎｍの波長の光に対しては正面方向では０ｎｍ、３０°傾斜させて測定したときの位相差は約１７０ｎｍ（＞λ／８）であった。
【０１５４】
さらに、このポジティブＣプレートを実施例１のネガティブＣプレート層に代えて用いる以外は実施例１と同様にして偏光素子を得た。得られた偏光素子を実施例１と同様に用いて性能を評価したところ、実施例１とおおよそ同等であった。
【０１５５】
（実施例３）
以下のようにして、反射直線偏光子と１／４波長板とＣプレートとを含む偏光素子を作製し、その性能を評価した。
【０１５６】
まず、反射直線偏光子を作製した。すなわち、まず、ポリエチレンナフタレート（ＰＥＮ）と、ナフタレンジカルボン酸−テレフタル酸コポリエステル（ｃｏ−ＰＥＮ）とが交互に積層するよう、薄膜をフィードブロック法で厚み制御しながら交互に積み重ね、２０層積層した多層膜を得た。さらにこの多層膜を一軸延伸した。この時の延伸温度は約１４０度、延伸倍率はＴＤ方向に約３倍であった。こうして得られた延伸フィルム中の各薄層の厚みは概略０．１μｍ程度であった。この２０層積層フィルム延伸品をさらに５枚積層し、計１００枚積層品として目的の反射直線偏光子（反射偏光子Ｂとする）を得た。反射偏光子Ｂは、全体の反射率により、５００ｎｍ以上６００ｎｍ以下の波長帯域における直線偏光に対して反射機能を有する。
【０１５７】
さらに、反射偏光子Ｂを用いて偏光素子を作製した。すなわち、まず、ネガティブＣプレート層を実施例１と同様にして作製し、その両側にポリカーボネート製一軸延伸フィルムから成る１／４波長位相差板（日東電工製、ＮＲＦフィルム（商品名）、５５０ｎｍで位相差（面内位相差）１３５ｎｍ）を接着し、さらにその外側に反射偏光子Ｂを接着して目的の偏光素子を得た。各層の貼り合せ角度は、入射側の反射偏光子Ｂの透過偏光軸方向を０°として、入射側の１／４波長板の面内遅相軸方向が４５°、Ｃプレートは軸方位無し、出射側の１／４板の面内遅相軸方向が−４５°、出射側の偏光子の透過偏光軸方向が９０°となるように貼り合せた。また、各層の接着は、各層間にアクリル系粘着剤（日東電工製Ｎｏ．７）を２５μｍ厚に塗布して行ない、ネガティブＣプレート層からは配向基板は剥離して液晶含有層のみを用いた。得られた偏光素子を実施例１と同様に用いて性能を評価したところ、実施例１とおおよそ同等であった。
【０１５８】
（実施例４）
以下のようにして、反射直線偏光子と１／２波長位相差板とを含む偏光素子を作製し、その性能を評価した。すなわち、まず、実施例３と同様にして作製した反射偏光子Ｂを２つと、ポリカーボネート製フィルム（鐘淵化学製）を二軸延伸して得られた正面位相差２７０ｎｍ（計測波長５５０ｎｍ）、Ｎｚ係数２．０の位相差フィルム（１／２波長板）とを準備した。そして、前記１／２波長板を前記２つの反射偏光子Ｂにより挟む配置でこれら各層を接着して目的の偏光素子を得た。各層の貼り合せ角度は、入射側の反射偏光子Ｂの透過偏光軸方向を０°として、１／２波長板の面内遅相軸方向が４５°、出射側の偏光子の透過偏光軸方向が９０°となるように貼り合せた。各層の接着は、各層間にアクリル系粘着剤（日東電工製Ｎｏ．７）を２５μｍ厚に塗布して用いて行なった。この偏光素子を実施例３と同様に評価したところ、実施例３と同等の性能を有する事が分かった。
【０１５９】
（実施例５）
以下のようにして、広波長領域に選択反射波長帯域を有する反射円偏光子（広帯域反射円偏光子）を作製し、さらに、それとＣプレートとを用いて偏光素子を作製して性能を評価した。
【０１６０】
まず、広帯域反射円偏光子を作製した。すなわち、まず、下記構造式で表されるネマチックモノマーＡ（前記と同様の物）およびカイラルモノマーＢを準備した。
【化２】

【化３】

【０１６１】
次に、前記ネマチックモノマーＡとカイラルモノマーＢとを所定の比で混合して重合させ、さらにそれを用いてコレステリック液晶層を作製した。さらに、ネマチックモノマーＡとカイラルモノマーＢとの混合比を変えて、選択反射波長帯域が異なるコレステリック液晶層を４層作製した。作製にあたっては、欧州特許出願公開０８３４７５４号明細書を参照した。具体的には以下の通りである。
【０１６２】
まず、ネマチックモノマーＡとカイラルモノマーＢとの混合比（重量比）およびそれから計算される各コレステリック液晶層の選択反射波長帯域とその中心波長とは下記表１の通りである。

【０１６３】
次に、ネマチックモノマーＡとカイラルモノマーＢとを重合させてコレステリック液晶化合物を合成した。すなわち、まず、表１に示すそれぞれの組成による混合物を、それぞれ３３ｗｔ％テトラヒドロフラン溶液とし、さらに０．５ｗｔ％の反応開始剤（アゾビスイソブチロニトリル）を添加した。これを６０℃で窒素パージした後、定法により重合処理し、生成物をジエチルエーテルで再沈分離し精製して目的のコレステリック液晶化合物を得た。
【０１６４】
一方、８０μｍ厚トリアセチルセルロース（ＴＡＣ）フィルム（富士写真フィルム工業製、ＴＤ−ＴＡＣ（商品名））を準備し、その表面に約０．１μｍ厚さのポリイミド層を塗工し、そのポリイミド層表面をレーヨン製ラビング布でラビング処理して配向基板とした。次に、そのラビング処理面上に、前記コレステリック液晶化合物の１０ｗｔ％塩化メチレン溶液を、ワイヤーバーで乾燥後の厚みが１．５μｍとなるように塗布した。これを１４０℃で１５分間加熱処理し、その後室温で放冷してコレステリック液晶化合物の配向状態を固定させ、コレステリック液晶層を得た。合成した各コレステリック液晶化合物についてそれぞれ上記の操作を行ない、表１に示す各選択反射波長帯域を有するコレステリック液晶層をそれぞれ得た。
【０１６５】
そして、得られた４層のコレステリック液晶層を短波長側から順番に接着し、約１０μｍ厚の液晶複合層を得て目的の広帯域反射円偏光子とした。接着は、透明イソシアネート系接着剤（特殊色料工業製、ＡＤ２４４（商品名））を各液晶層表面に塗布し、接着後に片側の配向基板（ＴＡＣフィルム）を剥離するという方法で順次行なった。得られた広帯域反射円偏光子の選択反射機能を測定したところ、４３０ｎｍ〜７１０ｎｍで選択反射機能を有していることが分かった。
【０１６６】
そして、Ｃプレート層を実施例１と同様にして作製し、その両側に前記広帯域反射円偏光子を接着して目的の偏光素子を得た。接着は、透光性粘着剤（日東電工製Ｎｏ．７）を各層間に２５μｍ厚に塗布し、実施例１と同様の操作により行なった。なお、上下の反射円偏光子で、透過する（反射する）円偏光の回転方向が同じになるようにした。
【０１６７】
次に、本実施例の偏光素子の性能を実施例１と同じ方法で評価した。緑色拡散光源を用いた評価では、実施例１の偏光素子と同様の集光性能を有していることが確認された。また、３波長冷陰極管を用いた液晶表示装置用バックライトによる評価でも実施例１と同様に優れた集光性能を示したが、本実施例の偏光素子は、可視光全域で同様の集光性能を発揮する点で実施例１の偏光素子よりもさらに優れていることが分かった。
【０１６８】
さらに、別のバックライト（冷陰極管を用いた直下型バックライト、多摩電気工業製）上に本実施例の偏光素子を配置し、集光性能を評価した。この場合も法線方向には光線が出射されるが斜め３０°以上では透過光線が減少した。そして、可視光全域で同様の集光性能を発揮することが分かった。
【０１６９】
（実施例６）
Ｃプレート層の厚みおよび位相差値を変える以外は実施例５と同様にして偏光素子を作製し、さらに実施例５と同様に集光性能を評価した。本実施例では、Ｃプレートの厚みは、４μｍとし、その位相差を測定したところ、正面位相差１ｎｍ、３０°傾斜時の位相差１００ｎｍ（＞λ／８）であった。
【０１７０】
図１６に、実施例５および６の偏光素子をそれぞれ拡散光源と組み合せて偏光光源とした場合、および前記拡散光源のみを用いた場合のそれぞれにおける出射光線の出射角度と相対輝度との関係を併せて示す。同図から、いずれの偏光素子も優れた集光性能を示しはするが、実施例５の方がより集光角度がシャープで正面の輝度上昇も大きいと分かる。
【０１７１】
（実施例７）
実施例５の偏光素子を液晶表示装置に組み込み、その表示性能を評価した。具体的には以下の通りである。まず、液晶表示装置としては、東芝製DynabookＳＳ３４３０（商品名）から得たＴＦＴ液晶表示装置（対角１１．３インチ）を準備した。この装置は、サイドライト型導光体の光源を用い、プリズムシートにより正面に集光するタイプである。次に、この液晶表示装置からプリズムシートを除去し、装置裏面側偏光子に対し、偏光軸に４５°の角度で１／４波長板（日東電工製ＮＲＦ−１４０（商品名））を接着し、さらにその上に実施例５で得られた偏光素子を接着した。接着は、透光性粘着剤（日東電工製Ｎｏ．７）を厚み２５μｍに塗布して行なった。このようにして市販の液晶表示装置を加工し、実施例５の偏光素子が組み込まれた目的の液晶表示装置を得た。得られた偏光素子付き液晶表示装置の性能を加工前（プリズムシート使用時）と比較したところ、正面への集光特性はプリズムシート使用時と同等であり、さらに、加工前よりも正面輝度が２０％向上していることが分かった。この結果は、プリズムシート等の従来技術に対する本発明の偏光素子の優位性を示す。
【０１７２】
（比較例１）
Ｃプレート層を用いず、２層の反射円偏光子を直接貼り合せる以外は実施例１と同様にして偏光素子を作製した。この偏光素子の性能を評価したところ、単一の反射円偏光子と同様の光学機能しか得られず、斜め方向での選択的な反射率の向上や透過率の低下のような現象は見られなかった。
【０１７３】
（比較例２）
Ｃプレート層の代わりに１／４波長板を用いる以外は実施例１と同様にして偏光素子を作製した。前記１／４波長板としては、ポリカーボネート製フィルムの延伸フィルムからなる正面位相差λ／４、Ｎｚ係数＝１．０のＡプレート（日東電工製ＮＲＦ−１４０フィルム（商品名）、厚み５０μｍ）を用いた。得られた偏光素子の性能を評価したところ、正面透過率が実施例１と比べて約１／２に低下する他、斜め入射方向の透過率が下がらず、集光や平行光化の機能は有さなかった。
【０１７４】
（比較例３）
市販のヨウ素系吸収２色性偏光子（日東電工製、ＮＰＦ−ＥＧ１４２５ＤＵ（商品名））を反射偏光子Ｂに代えて用いる以外は実施例３と同様にして偏光素子を得た。この偏光素子の性能を評価したところ、正面方向の透過特性と斜め方向の吸収特性による視野角制限効果は得られるが、吸収損失が著しく、正面の明るさは向上しなかった。
【０１７５】
（ライトテーブルを用いた輝度評価）
実施例１〜６および比較例１〜３の各偏光素子を、市販のライトテーブル（ハクバ製、３波長蛍光灯、直下型拡散光源）上に配置し、鉛直上方における輝度（２°視野）を輝度計（トプコン製、ＢＭ７（商品名））を用いて測定した。測定値はライトテーブルのみで測定した時の値を１００として規格化した。測定結果を表２に示す。
【０１７６】
（表２）
相対輝度
実施例１ ８０
実施例２ ７８
実施例３ ７２
実施例４ ７０
実施例５ ８２
実施例６ ９０
比較例１ ６７
比較例２ ２１
比較例３ ３９
【０１７７】
表２から分かる通り、実施例の偏光素子は、ライトテーブルに用いた場合も正面方向に対する優れた輝度向上効果を示した。なお、実施例の偏光素子は、図１６および１７に示した通り、液晶表示装置用の直下型バックライトに用いた場合は正面の相対輝度が１００（元のバックライトの正面輝度）を上回っていたが、表２での相対輝度は１００をやや下回っていた。これは、市販ライトテーブルでは前記直下型バックライトの場合と比較して反射偏光子で反射された戻り光が再び法線方向へ戻る効率がやや悪いためである。しかし、比較例の偏光素子と比べれば著しく優れた正面方向の輝度向上効果を有していることが分かる。
【０１７８】
【発明の効果】
以上説明した通り、本発明の偏光素子によれば、正面輝度に寄与する垂直入射光の透過偏光特性を害することなく斜め透過光を効率的に光源側へ反射できる。また、前記光源側へ反射した斜め透過光（反射偏光）を正面輝度の向上に寄与しうる光に変換することでさらに輝度を向上させることも可能である。そして、反射偏光子の選択反射波長帯域を調整することにより、前記の効果を広い波長領域で波長依存性が少なく発揮することもできる。さらに、本発明の偏光素子は、従来技術の干渉フィルターと輝線発光光源の組み合わせによる平行光化および集光システム等と比べて光源の特性に対する依存性が少ないため、あらゆる偏光光源および画像表示装置に使用することができる。例えば、液晶表示素子のバックライト側の偏光子として利用した場合には、明るい視認性に優れた表示を得ることが可能である。また、光源から出射された拡散光の光利用効率に優れるため、高輝度の偏光光源装置、有機ＥＬ表示装置、ＰＤＰ、ＣＲＴ等の画像表示装置を形成することもできる。
【図面の簡単な説明】
【図１】本発明の偏光素子において、反射円偏光子とＣプレートとを組み合わせた一実施形態の集光性と輝度向上の同時発現のメカニズムを示す図である。
【図２】本発明における自然光、円偏光および直線偏光を表す記号について説明した図である。
【図３】直線偏光子と１／４波長板の組み合わせによる円偏光化の模式図である。
【図４】本発明の偏光素子において、反射直線偏光子とＣプレートと１／４波長板とを組み合わせた一実施形態の集光性と輝度向上の同時発現のメカニズムを示す図である。
【図５】図４の偏光素子における各層がなす角度を示す模式図である。
【図６】本発明の偏光素子において、反射直線偏光子とＮｚ≧２である１／４波長板とを組み合わせた一実施形態の集光性と輝度向上の同時発現のメカニズムを示す図である。
【図７】図６の偏光素子における各層がなす角度を示す模式図である。
【図８】本発明の偏光素子において、反射直線偏光子とＮｚ≧１．５である１／２波長板とを組み合わせた一実施形態の集光性と輝度向上の同時発現のメカニズムを示す図である。
【図９】図８の偏光素子における各層がなす角度を示す模式図である。
【図１０】ネガティブＣプレートの光学特性の一例を示す模式図である。
【図１１】ホメオトロピック配向した液晶分子を含む位相差層の模式図である。
【図１２】ディスコチック液晶を含む位相差層の模式図である。
【図１３】無機層状化合物を含む位相差層の模式図である。
【図１４】本発明の偏光素子において、反射直線偏光子とＣプレートと１／４波長板とを組み合わせた場合の各層の貼り合せ角度の一例を示す図である。
【図１５】図１４の偏光素子における光の変換経路をポアンカレ球で示した説明図である。
【図１６】実施例１の偏光素子の集光および輝度向上性能を示す図である。
【図１７】実施例５および６の偏光素子の集光および輝度向上性能を示す図である。
【符号の説明】
１〜５８ 自然光、円偏光または直線偏光
２０１、２０３ 反射円偏光子
２０２ Ｃプレート
３０１ 自然光
３０２ 直線偏光子
３０３ 直線偏光
３０４ １／４波長板
３０５ 円偏光
４０４、４０８ 反射直線偏光子
４０５、４０７ １／４波長板
４０６ Ｃプレート
６０９、６１２ 反射直線偏光子
６１０、６１１ １／４波長板
８１３、８１５ 反射直線偏光子
８１４ １／２波長板
１１０１、１２０１ 液晶分子
１３０１ 負の一軸性配向結晶体薄片
１４０１、１４０５ 反射直線偏光子
１４０２、１４０４ １／４波長板
１４０３ Ｃプレート[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polarizing element, and more specifically, it is excellent in the light use efficiency of diffused light emitted from a light source, and is a high-intensity polarized light source, various image devices such as a liquid crystal display device with good visual recognition, an organic EL display device, The present invention relates to a polarizing element suitable for use in PDP, CRT and the like.
[0002]
[Prior art]
In order to improve the visibility of an image display device, a technique for improving luminance by collecting light emitted from a light source in a front direction is generally used. More specifically, for example, a lens, a mirror (reflective layer), a prism, or the like is used, and light is condensed and collimated using refraction or reflection to improve luminance.
[0003]
For example, in a liquid crystal display device, light emitted from a light source is condensed in a front direction by a prism sheet or the like and efficiently incident on a liquid crystal display element to improve luminance. However, when the light is collected by the prism sheet, a large difference in refractive index is necessary in principle, and therefore, it is necessary to install it through an air layer or the like. For this reason, light loss due to unnecessary reflection or scattering may be caused, and there is a problem that a large number of parts are required.
[0004]
Furthermore, as a technique for improving the emission luminance of polarized light, a luminance enhancement system using retroreflection has been proposed. Specifically, this brightness enhancement system is a system in which a reflective layer is provided on the lower surface of the light guide plate, and a reflective polarizer is provided on the exit surface. Then, the incident light in the system is separated into transmitted light and reflected light according to the polarization state, and the reflected light is reflected through the reflection layer on the lower surface of the light guide plate and re-emitted from the exit surface to improve the brightness. Let For example, circularly polarized light reflection separation by cholesteric liquid crystal is detailed in Patent Documents 1 to 3 and the like. However, such a brightness enhancement system has a problem in that it is difficult to obtain a sufficient effect for a light source whose light-condensing property has been improved by a prism sheet or the like in comparison with a light source having strong diffusivity. is there.
[0005]
In order to solve the above-described problems, a brightness enhancement technique for collimating light from a light source using a special optical film instead of using a lens, a mirror, a prism, or the like has been studied. As a typical method, for example, there is a method performed by a combination of a bright line light source and a band pass filter. More specifically, there is a method of arranging a band-pass filter on a light source or display device that emits bright lines such as CRT or electroluminescence, as in, for example, Patent Documents 4 to 12 or 13 to 14 of Philips. Further, as disclosed in Patent Document 15 of Fuji Photo Film Industry Co., Ltd., there is a method of arranging a bandpass filter corresponding to three wavelengths with respect to the bright line type cold cathode tube. However, these techniques have a problem that the light source does not function unless it has an emission line spectrum, and a problem related to the design and manufacture of a film that functions selectively for a specific wavelength. Further, a vapor deposition interference film is often used as the band-pass filter, but there is a risk that the wavelength characteristic may change due to a change in the refractive index of the thin film in a humidified environment.
[0006]
On the other hand, as a collimation system using a hologram material, for example, a system described in Patent Document 16 of Rockwell Corporation can be cited. However, although this type of material has a high front transmittance, there is a problem that the reflection removal rate of obliquely incident light is not so high. When the direct transmittance is obtained by entering parallel light into such a system, the transmittance is measured high because it passes through in the front direction, while the transmittance is measured low due to scattering of the obliquely incident light. No difference occurs on the diffuse light source. For this reason, there are cases where the light collecting function cannot always be sufficiently achieved when the light source is disposed on an actual diffuse backlight source. Further, the hologram material has problems such as durability and reliability due to its physical properties.
[0007]
[Patent Document 1]
JP-A-3-45906
[0008]
[Patent Document 2]
JP-A-6-324333
[0009]
[Patent Document 3]
Japanese Patent Laid-Open No. 7-36032
[0010]
[Patent Document 4]
JP-A-6-235900
[0011]
[Patent Document 5]
Japanese Patent Laid-Open No. 02-158289
[0012]
[Patent Document 6]
Japanese National Patent Publication No. 10-510671
[0013]
[Patent Document 7]
US Pat. No. 6,307,604
[0014]
[Patent Document 8]
German patent 3836955
[0015]
[Patent Document 9]
German Patent No. 4220289
[0016]
[Patent Document 10]
EP 578302
[0017]
[Patent Document 11]
US Patent Application Publication No. 2002/0034009
[0018]
[Patent Document 12]
International Publication No. 02/25687 Pamphlet
[0019]
[Patent Document 13]
US Patent Application Publication No. 2001/521443
[0020]
[Patent Document 14]
US Patent Application Publication No. 2001/516066
[0021]
[Patent Document 15]
US Patent Application Publication No. 2002/0036735
[0022]
[Patent Document 16]
US Pat. No. 4,984,872
[0023]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a polarizing element that can efficiently reflect obliquely transmitted light toward the light source without impairing the transmission polarization characteristics of vertically incident light.
[0024]
[Means for Solving the Problems]
  In order to solve the above-described problem, the polarizing element of the present invention includes at least two reflective polarizers and a retardation layer disposed therebetween, and the two reflective polarizers are clockwise circularly polarized light. And a reflective circular polarizer that selectively transmits one of the left-handed circularly polarized light and selectively reflects the other, and the two-layer reflective circular polarizer has at least one of the selective reflection wavelength bands in the selective reflection of polarized light. Parts overlap each other,The rotational directions of the circularly polarized light passing through the two layers of reflective circular polarizers are the same,The retardation layer is a polarizing element that satisfies the conditions of the following formulas (I) and (II).
[0025]
R ≦ (λ / 10) (I)
R ′ ≧ (λ / 8) (II)
[0026]
In formulas (I) and (II):
λ is the wavelength of light incident on the retardation layer,
R is an absolute value of a phase difference (in-plane phase difference) between the X-axis direction and the Y-axis direction with respect to incident light from the Z-axis direction (normal direction), and the X-axis direction is the retardation layer. Is the direction (in-plane slow axis direction) in which the refractive index is maximum, and the Y-axis direction is a direction (in-plane advance phase) perpendicular to the X-axis direction in the plane of the retardation layer. The Z-axis direction is the thickness direction of the retardation layer perpendicular to the X-axis direction and the Y-axis direction,
R ′ is an absolute value of the phase difference between the X′-axis direction and the Y′-axis direction with respect to incident light from a direction inclined by 30 ° or more with respect to the Z-axis direction, and the X′-axis direction is the Z-axis direction. It is an axial direction in the retardation layer plane perpendicular to the incident direction of incident light inclined by 30 ° or more with respect to the direction, and the Y′-axis direction is a direction perpendicular to the incident direction and the X′-axis direction. .
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described.
[0028]
As a result of intensive studies, the present inventors have been able to efficiently reflect obliquely transmitted light to the light source side without impairing the transmission polarization characteristics of vertically incident light that contributes to front luminance by the polarizing element of the present invention having the above-described configuration. I found. Further, it is possible to further improve the luminance by converting the obliquely transmitted light (reflected polarized light) reflected to the light source side into light that can contribute to the improvement of the front luminance. Furthermore, the polarizing element of the present invention has such a light collecting property and a luminance improving function by retroreflection, so that the light source type dependency on the light collecting function and the collimating function is small.
[0029]
In the retardation layer of the present invention, the in-plane retardation R is (λ / 10) or less as described above, but from the viewpoint of maintaining the polarization state of incident light from the Z-axis direction (normal direction) as much as possible. The smaller one is better, preferably λ / 20 or less, more preferably λ / 50 or less, ideally 0. A retardation layer having no or very small in-plane retardation and having a retardation only in the thickness direction is called a C-plate, and the optical axis is in the thickness direction perpendicular to the in-plane direction. Exists. The C-plate is called a positive (positive) C-plate when the optical characteristic condition satisfies the following formula (VI), and is called a negative (negative) C-plate when the optical characteristic condition satisfies the following formula (VII). Typical negative C plates include, for example, biaxially stretched polycarbonate (PC) and polyethylene terephthalate (PET) films, cholesteric liquid crystals with selective reflection wavelength bands set shorter than visible light, and discotic liquid crystals. Examples thereof include a film obtained by parallel orientation and an in-plane orientation of an inorganic crystal compound having a negative retardation. A typical positive C plate is, for example, a vertically aligned liquid crystal film.
[0030]
nx≈ny <nz (VI)
nx≈ny> nz (VII)
[0031]
In the present invention, nx, ny, and nz represent the refractive indexes in the X-axis, Y-axis, and Z-axis directions in each optical layer such as the C-plate, and the X-axis direction is the in-plane of the layer. The Y-axis direction is a direction perpendicular to the X-axis direction (in-plane fast axis direction) in the plane of the layer. The Z-axis direction is the thickness direction of the layer perpendicular to the X-axis direction and the Y-axis direction.
[0032]
The retardation layer in the present invention is not particularly limited as long as it satisfies the optical property conditions of the above formulas (I) and (II). For example, the retardation layer includes a cholesteric liquid crystal compound fixed in a planar alignment state. The selective reflection wavelength band of the phase difference layer is preferably present in a wavelength region other than the visible light region (380 nm to 780 nm). Here, the reason why the selective reflection wavelength band is a wavelength region other than the visible light region (380 nm to 780 nm) is to prevent coloring or the like in the visible light region. The selective reflection wavelength band of the cholesteric liquid crystal layer can be uniquely determined from the cholesteric chiral pitch and the refractive index of the liquid crystal, and the central wavelength λ of selective reflection is represented by the following formula (VIII).
[0033]
λ = np (VIII)
[0034]
In formula (VIII), n is the average refractive index of cholesteric liquid crystal molecules, and p is the chiral pitch.
[0035]
The value of the center wavelength of the selective reflection wavelength band may exist on the longer wavelength side than the visible light region, for example, in the near infrared region, but if it exists in the ultraviolet region of 350 nm or less, it is affected by the optical rotation. There is no risk of complicated phenomena, which is more preferable.
[0036]
The kind of the cholesteric liquid crystal is not particularly limited and may be appropriately selected. Examples thereof include a polymer liquid crystal obtained by polymerizing a liquid crystal monomer, a liquid crystal polymer exhibiting cholesteric liquid crystallinity at a high temperature, and a mixture thereof. The liquid crystallinity of the cholesteric liquid crystal may be either lyotropic or thermotropic, but is more preferably a thermotropic liquid crystal from the viewpoint of ease of control and ease of forming a monodomain. Moreover, the manufacturing method of the said cholesteric liquid crystal is not specifically limited, either, A well-known method can be used suitably. The material that can be used for the production of the partially crosslinked polymer material having cholesteric liquid crystallinity is not particularly limited and is arbitrary. For example, JP 2002-533742 (WO00 / 37585), EP358208 (US521118), EP66137 (US4388453) And the like. Furthermore, a cholesteric liquid crystal can be obtained, for example, by mixing a nematic liquid crystal monomer or a polymerizable mesogenic compound with a chiral agent and reacting them. The polymerizable mesogenic compound is not particularly limited, and examples thereof include compounds described in WO 93/22397, EP 0261712, DE 19504224, DE 4408171, and GB 2280445, and may be non-chiral compounds or chiral compounds. Any of these may be used and can be synthesized by a known method. Specific examples of the polymerizable mesogenic compound include, for example, LC242 (trade name) manufactured by BASF, E7 (trade name) manufactured by Merck, and LC-Silicon-CC3767 (trade name) manufactured by Wacker-Chem. The chiral agent is not particularly limited, but can be synthesized by the method described in WO98 / 00428, for example. Specific examples of the chiral compound include non-polymerizable chiral compounds such as S101, R811 and CB15 (all trade names) from Merck, and chiral agents such as LC756 (trade name) from BASF.
[0037]
A method for producing the retardation layer containing the cholesteric liquid crystal compound is not particularly limited, and a conventional cholesteric liquid crystal layer forming method can be used as appropriate. For example, a base material on which an alignment film is formed on its surface, or itself is used. There is a method in which a cholesteric liquid crystal compound is applied and aligned on a substrate having liquid crystal alignment ability, and the alignment state is fixed.
[0038]
The base material, for example, a film of polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, polyetherimide, etc. is formed on a base material having a birefringence retardation as small as possible, such as triacetyl cellulose or amorphous polyolefin, A rubbing treatment with a rayon cloth or the like to form an alignment film, or a similar substrate with SiO 2₂And forming an orientation film by forming an oblique vapor deposition layer or the like. In addition, the base material which extended the film of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), etc., and gave liquid crystal alignment ability, and the extended base material surface was further processed with fine abrasives such as Bengala and rubbing cloth. Examples thereof include a substrate on which fine irregularities having fine alignment regulating force are formed, and a substrate in which an alignment film that generates liquid crystal regulating force by light irradiation such as an azobenzene compound is formed on the stretched substrate.
[0039]
A specific method for forming a retardation layer containing a cholesteric liquid crystal compound on the substrate is, for example, as follows. That is, first, a liquid crystal polymer solution is applied on the surface of the substrate having liquid crystal alignment ability and dried to form a liquid crystal layer. Although the solvent of the solution is not particularly limited, for example, a chlorine solvent such as methylene chloride, trichloroethylene, tetrachloroethane, a ketone solvent such as acetone, methyl ethyl ketone (MEK), cyclohexanone, an aromatic solvent such as toluene, cycloheptane, and the like. Examples include cyclic alkanes, amide solvents such as N-methylpyrrolidone, and ether solvents such as tetrahydrofuran. These may be used alone or in combination of two or more. The coating method is not particularly limited, and for example, a spin coating method, a roll coating method, a flow coating method, a printing method, a dip coating method, a casting film forming method, a bar coating method, a gravure printing method, and the like can be used as appropriate. . Further, instead of the solution, a heated melt of a liquid crystal polymer, preferably a heated melt exhibiting an isotropic phase, is applied in the same manner, and further developed into a thin layer while maintaining the melting temperature as necessary. A method such as solidification may be used. Such a method has an advantage that the working environment has good hygiene and the like because no solvent is used.
[0040]
Then, the alignment state of the cholesteric liquid crystal molecules in the liquid crystal layer is fixed to obtain a target retardation layer. The immobilization method is not particularly limited, and an appropriate method may be selected depending on the case. For example, the liquid crystal layer is heated to a glass transition temperature or higher and lower than an isotropic phase transition temperature so that the liquid crystal polymer molecules are planarized. There is a method in which the glass is cooled to below the glass transition temperature in the oriented state to obtain a glass state and solidified. Alternatively, the structure may be fixed by energy irradiation such as ultraviolet rays or ion beams at the stage where the alignment state is formed. In the above step, the liquid crystal monomer may be used in place of the liquid crystal polymer, or may be used in combination with the liquid crystal polymer and aligned, and then polymerized by irradiation with ionizing radiation such as an electron beam or ultraviolet rays or heat to obtain a polymerized liquid crystal. At this time, a chiral agent, an alignment aid or the like may be added as necessary.
[0041]
For example, when the birefringence is small, the substrate may be used in a polarizing element integrally with the retardation layer containing the cholesteric liquid crystal compound. In addition, when the thickness of the base material or the size of birefringence may hinder the function of the polarizing element, the retardation layer is peeled off from the base material or transferred onto another base material. May be used.
[0042]
The retardation layer is also preferably a retardation layer containing a rod-like liquid crystal compound fixed in a homeotropic alignment state. The type of the homeotropic liquid crystal is not particularly limited and may be appropriately selected. Examples thereof include a polymer liquid crystal obtained by polymerizing a liquid crystal monomer, a liquid crystal polymer exhibiting nematic liquid crystal properties at a high temperature, and a mixture thereof. The polymerized liquid crystal can be obtained by adding an alignment aid or the like to the liquid crystal monomer as necessary, and polymerizing by irradiation with ionizing radiation such as an electron beam or ultraviolet rays or heat. The liquid crystallinity may be either lyotropic or thermotropic, but is preferably a thermotropic liquid crystal from the viewpoint of ease of control and ease of formation of a monodomain. Although it does not specifically limit as a liquid crystal monomer, For example, there exists a polymerizable mesogen compound. The polymerizable mesogenic compound is not particularly limited, but is the same as the cholesteric liquid crystal, for example.
[0043]
The method for forming such a retardation layer is not particularly limited, and a known method can be used as appropriate. For example, it can be formed using an alignment film or the like in the same manner as in the case of the cholesteric liquid crystal. . Homeotropic alignment is obtained, for example, by applying the homeotropic liquid crystal on a film on which a vertical alignment film (long-chain alkylsilane or the like) is formed, and expressing and fixing the liquid crystal state.
[0044]
Further, as the retardation layer, a retardation layer containing a discotic liquid crystal compound fixed in a nematic phase or columnar phase alignment state is also preferable. Such a retardation layer, for example, exhibits a nematic phase or columnar phase from a discotic liquid crystal material having negative uniaxial properties such as phthalocyanines and triphenylene compounds having a molecular extension in the plane, Can be fixed. A specific formation method is not particularly limited, and a known method can be appropriately used.
[0045]
Furthermore, the retardation layer includes an inorganic layered compound having negative uniaxiality, and the orientation state of the inorganic layered compound is a direction in which the optical axis direction of the retardation layer is perpendicular to the surface (normal direction). A retardation layer that is fixed so as to become is also preferable. A method for forming such a retardation layer is not particularly limited, and a known method can be used as appropriate. The negative uniaxial inorganic layered compound is described in detail in JP-A-6-82777.
[0046]
11 to 13 show a retardation layer in which the homeotropic alignment state is fixed, a retardation layer using a discotic liquid crystal, and a retardation layer made of an inorganic layered compound. In the figure, the figures denoted by reference numerals 1101, 1201 and 1301 represent homeotropic liquid crystal molecules, discotic liquid crystal molecules, and flakes of negative uniaxial inorganic layered compound crystals, respectively.
[0047]
Furthermore, as the retardation layer, a retardation layer containing a biaxially oriented non-liquid crystal polymer is also preferable. The method for forming such a retardation layer is not particularly limited, and a known method can be used as appropriate. For example, a method of biaxially stretching a polymer film having positive refractive index anisotropy in a balanced manner, Examples thereof include a method of pressing a plastic resin and a method of cutting out from a parallel oriented crystal. Moreover, depending on the kind of non-liquid crystal polymer, C-plate may be obtained by apply | coating the solution on a base material, drying, and shape | molding in a film form. The non-liquid crystal polymer is not particularly limited, and examples thereof include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, polystyrene, acrylonitrile / styrene. Styrenic polymer such as copolymer (AS resin), polycarbonate polymer such as bisphenol A / carbonic acid copolymer, linear or branched polyolefin such as polyethylene, polypropylene, ethylene / propylene copolymer, polynorbornene, etc. Polyolefins containing a cyclo structure, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers, polyethersulfone Polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers, and epoxy polymers are preferred. Two or more types may be used in combination. Furthermore, an appropriate additive may be appropriately added to these polymer materials for any purpose such as imparting extensibility and shrinkage.
[0048]
Other examples of the non-liquid crystal polymer include a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and cyano group in the side chain. Also included are compositions. Examples of such a resin composition include a resin composition having an alternating copolymer composed of isobutene and N-methylenemaleimide and an acrylonitrile / styrene copolymer. Furthermore, as a polyimide film material, for example, materials described in US Pat. No. 5,580,950 and US Pat. No. 5,580,964 can be suitably used as a retardation layer made of a non-liquid crystalline polymer.
[0049]
Next, in the polarizing element of the present invention, the two-layer reflective polarizer selectively transmits one of clockwise circularly polarized light and counterclockwise circularly polarized light and selectively reflects the other (reflected circularly polarized light). By being a child, it has an advantage that it has a polarization separation function for natural light incident from a wide angle and is easy to design and manufacture.
[0050]
Although it does not specifically limit as said reflective circular polarizer, For example, what fixed the planar orientation state of the cholesteric liquid crystal is more preferable. The kind of the cholesteric liquid crystal is not particularly limited and can be appropriately selected. For example, similarly to the retardation layer, a polymerized liquid crystal obtained by polymerizing a liquid crystal monomer, a liquid crystal polymer exhibiting cholesteric liquid crystal properties at a high temperature, and those A mixture of the above can be used. The polymerized liquid crystal can be prepared by adding a chiral agent, an alignment aid or the like to a liquid crystal monomer as necessary, and polymerizing by irradiation with ionizing radiation such as an electron beam or ultraviolet rays or heat. The liquid crystallinity of the cholesteric liquid crystal may be either lyotropic or thermotropic, but is more preferably a thermotropic liquid crystal from the viewpoint of ease of control and ease of forming a monodomain.
[0051]
More specifically, examples of the reflective circular polarizer include a sheet including a layer made of a cholesteric liquid crystal polymer, a sheet in which the layer is laminated on a glass plate, a film made of a cholesteric liquid crystal polymer, and the like. However, it is not limited to these. A method for forming such a cholesteric liquid crystal layer is not particularly limited, and for example, it can be formed in the same manner as the retardation layer containing the cholesteric liquid crystal compound. The cholesteric liquid crystal is more preferably aligned as uniformly as possible in the layer.
[0052]
In the reflective circular polarizer, it is more preferable that the selective reflection wavelength band covers the visible light range and the light source emission wavelength band from the viewpoint of the performance of the polarizing element, and the selective reflection wavelength band is a cholesteric chiral pitch as described above. It can be uniquely determined from the refractive index of the liquid crystal. Depending on the purpose, the cholesteric liquid crystal layer forming the reflective circular polarizer may be formed by laminating a plurality of layers having different selective reflection wavelength bands, or may be a single layer whose pitch is changed in the thickness direction. . When laminating a plurality of layers, for example, a plurality of layers in which a cholesteric liquid crystal layer is laminated on a substrate may be prepared in advance, and these may be further laminated. However, for example, a method of forming an alignment film on a cholesteric liquid crystal layer and laminating another cholesteric liquid crystal layer on the cholesteric liquid crystal layer is more preferable from the viewpoint of reducing the thickness.
[0053]
The polarizing element of the present invention further includes another layer having a quarter-wave plate function at least in the front direction, and this layer is a reflective circle located on the viewing side of the two-layer reflective circular polarizer. More preferably, it is disposed further outside the polarizer. By having this configuration, the circularly polarized light transmitted through the reflective circular polarizer can be changed to linearly polarized light and can be used efficiently. Such a polarizing element further includes an absorptive dichroic polarizing plate, and the absorptive dichroic polarizing plate is disposed on the outer side of another layer having a quarter-wave plate function in at least the front direction. It is particularly preferable.
[0054]
The absorptive dichroic polarizing plate is not particularly limited. For example, iodine or 2 may be 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. Examples thereof include an absorption polarizing plate stretched by adsorbing a dichroic substance such as a chromatic dye, and a polyene oriented film such as a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product. Moreover, the polarizing plate etc. which provided the transparent protective layer which consists of a plastic coating layer, a laminated layer of a film, etc. on the one or both surfaces of these films for the purpose of protection, such as water resistance, are also mentioned. Furthermore, the transparent protective layer contains transparent fine particles to give a fine concavo-convex structure on the surface. Examples of the transparent fine particles include inorganic fine particles such as silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle diameter of 0.5 to 5 μm. Further, organic fine particles such as a crosslinked or uncrosslinked polymer may also be used.
[0055]
(Embodiment 1)
Hereinafter, based on FIG. 1 and FIG. 2, the mechanism of simultaneous expression of the light condensing property and the brightness improvement in the polarizing element of the present invention will be described. However, this is only one embodiment of the present invention, and the present invention is not limited to this.
[0056]
FIG. 1 is a diagram showing the embodiment in the polarizing element of the present invention. As illustrated, this polarizing element includes a cholesteric liquid crystal circular polarizer 201 (hereinafter sometimes referred to as “layer 1”), a C-plate 202 (hereinafter sometimes referred to as “layer 2”), and a cholesteric liquid crystal circular polarizer. 203 (hereinafter also referred to as “layer 3”) are stacked in this order, and light enters from the layer 1 side. In the embodiment shown in the figure, the rotational directions of the circularly polarized light that pass through the two layers of the reflective circular polarizer are the same. In addition, since both the circular polarizer and the retardation layer have no optical axis in the in-plane direction, the bonding direction may be arbitrary. For this reason, the angle range for narrowing the collimated light has isotropic and symmetric characteristics.
[0057]
FIG. 2 is a diagram illustrating symbols representing natural light, circularly polarized light, and linearly polarized light in the present invention. The circularly polarized light a and the circularly polarized light b have opposite rotation directions, and the linearly polarized light c and the linearly polarized light d are orthogonal to each other.
[0058]
Hereinafter, an ideal operation principle when light is incident on the polarizing element of FIG. 1 will be described in order with reference to FIG.
(1) First, of the light supplied from a backlight (light source, not shown), vertically incident natural light 1 is polarized and separated by the circular polarizer 201 (layer 1), and transmitted light 3 and reflected light 2 are two. Divided into two circularly polarized light. The direction of rotation of each circularly polarized light is opposite.
(2) The transmitted light 3 passes through the retardation layer 202 (layer 2) and becomes transmitted light 4.
(3) The transmitted light 4 passes through the circular polarizer 203 (layer 3) and becomes transmitted light 5.
(4) The transmitted light 5 is used for a liquid crystal display device disposed thereon.
(5) Next, among the light supplied from the backlight, the obliquely incident natural light 6 is polarized and separated by the circular polarizer 201, and is divided into two circularly polarized light of transmitted light 8 and reflected light 7. The direction of rotation of each circularly polarized light is opposite.
(6) When the transmitted light 8 passes through the phase difference layer 202, a retardation value is given by ½ wavelength and becomes transmitted light 9.
(7) The transmitted light 9 has a rotational direction of circularly polarized light opposite to that of the light 8 due to the influence of the phase difference.
(8) The transmitted light 9 is reflected by the circular polarizer 203 to become light 10.
Note that circularly polarized light is generally known to reverse the direction of rotation when reflected (for example, WA Shurcliff, Polarized Light: Production and Use , (Harvard University Press, Cambridge, Mass., 1966))). However, as an exception, it is known that the direction of rotation does not change in the case of reflection on a cholesteric liquid crystal layer (see Baifukan “Liquid Crystal Dictionary” etc.). In this figure, since the reflection is performed on the cholesteric liquid crystal surface, the rotation directions of the circularly polarized light of the light 9 and the light 10 do not change.
(9) The reflected light 10 is affected by the phase difference when passing through the phase difference layer 202, and becomes the transmitted light 11.
(10) The rotation of the transmitted light 11 is reversed due to the influence of the phase difference.
(11) Since the rotation direction of the light 11 returns to the same direction as the light 8, the light 11 passes through the circular polarizer 201 and becomes the transmitted light 12.
(12) Lights 7 and 12 return to the backlight side and are recycled. These return rays are repeatedly reflected by a diffusing plate or the like disposed in the backlight until the rays can be transmitted in the vicinity of the normal direction of the polarizing element while randomly changing the traveling direction and the direction of polarization, thereby contributing to the improvement of luminance.
(13) When the transmitted circularly polarized light 5 is converted into linearly polarized light by a quarter wavelength plate (not shown), it can be used for a liquid crystal display device or the like without causing an absorption loss. As described above, light collection and luminance improvement are performed by the polarizing element of FIG.
[0059]
Next, the selective reflection wavelength band of the reflective polarizer will be described.
[0060]
The selective reflection wavelength bands of the two-layer reflective polarizers in the present invention may be the same or different. For example, one reflective polarizer may have reflection at all wavelengths of visible light and the other may partially reflect, but at least some of the selective reflection wavelength bands need to overlap each other. . The selective reflection wavelength band of the reflective polarizer may be appropriately designed according to the purpose of use of the polarizing element and the type of member or light source used in combination. For example, for light with a high visibility around a wavelength of 550 nm. On the other hand, it is preferable that the selective reflection is achieved. Specifically, it is preferable that a region where the selective reflection wavelength bands of the two-layer reflective polarizers overlap each other includes a wavelength range of 540 to 560 nm. In the case of a reflective polarizer containing a cholesteric liquid crystal compound, as described above, the selective reflection wavelength band can be uniquely determined from the cholesteric chiral pitch and the refractive index of the liquid crystal. ) (Λ = np).
[0061]
Furthermore, when it is necessary to obtain a color display, white light is required. Therefore, it is more preferable that the characteristics are uniform in the visible light region or at least the light emission spectrum region (mostly around 435 nm to 610 nm) of the light source can be covered. Considering that the selective reflection spectrum of cholesteric liquid crystal shifts to the short wavelength side (blue shift) with respect to obliquely incident light, the overlapping wavelength region covers a region having a wavelength longer than 610 nm. Further preferred. The selective reflection wavelength bandwidth necessary on the long wavelength side largely depends on the angle and wavelength of the incident light from the light source, so the long wavelength end is arbitrarily set according to the required specifications. Specifically, for example, in a backlight using a wedge-type light guide plate often used in a liquid crystal display device, the angle of light emitted from the light guide plate is an angle of about 60 ° from the normal direction. The amount of blue shift tends to increase as the incident angle increases, and is generally about 100 nm around 60 °. Therefore, when a three-wavelength cold cathode tube is used for the backlight and the red emission line spectrum is 610 nm, it is only necessary that the overlapping region of the selective reflection wavelength band reaches the longer wavelength side than 710 nm. . Further, from the viewpoint of coloring and compatibility with RGB in a liquid crystal display device or the like, it is particularly preferable that the selective reflection wavelength bands overlap in the entire visible light wavelength region, that is, 380 nm to 780 nm.
[0062]
When the backlight light source emits only a specific wavelength, for example, in the case of a colored cold cathode tube, it is only necessary to shield only the bright line obtained. In addition, when the emitted light from the backlight is focused to some extent in the front direction by the design of microlenses, dots, prisms, etc. processed on the trending body surface, the transmitted light at a large incident angle can be ignored. Therefore, the selective reflection wavelength need not be extended to the long wavelength side.
[0063]
Next, the retardation value of the retardation layer will be described.
[0064]
The oblique retardation value R ′ of the retardation layer (see the formula (II)) is ideally λ / 2 (λ) because the light transmitted through the retardation layer is totally reflected by the reflective polarizer. Is the wavelength of incident light), but in practice, the object can be achieved even if it is not strictly λ / 2. Furthermore, the oblique phase difference value R ′ varies depending on the incident angle of light and generally tends to increase as the incident angle increases. Therefore, in order to efficiently cause polarization conversion, the angle of total reflection is considered. Therefore, it is necessary to decide appropriately. For example, in order to achieve total reflection at an angle of about 60 ° from the normal line, the phase difference when measured at 60 ° may be determined to be about λ / 2. In addition, the adjustment method of the oblique direction retardation value R ′ is not particularly limited, and a known method can be used as appropriate. For example, when the retardation layer is a biaxially stretched film, the stretching ratio and the film thickness Etc. can be controlled.
[0065]
Furthermore, the transmitted light from the reflective polarizer may change its polarization state due to the C-plate-like birefringence of the reflective polarizer itself. For example, a reflective circular polarizer including a cholesteric liquid crystal layer may have some properties as a retardation layer, for example, a negative C plate, due to the twisted structure of the cholesteric liquid crystal compound. Therefore, the oblique phase retardation value R ′ of the retardation layer can be adjusted to a value smaller than λ / 2 in consideration of the retardation of the reflective polarizer. Specifically, R ′ may be λ / 8 or more as in the formula (II). The upper limit value of R ′ is not particularly limited, and may be set as appropriate according to the purpose as described above. As described above, the in-plane retardation R (see the formula (I)) should be as small as possible.
[0066]
For reference, FIG. 10 shows a refractive index ellipsoid that directly represents the relationship between the phase difference with respect to the incident angle of the C plate and the optical anisotropy of the C plate. However, this is only an example and does not limit the present invention. FIG. 10 shows an example in which the biaxial orientation of the birefringent resin is a front phase difference≈0 and an oblique phase difference = 1/2 wavelength. In this case, the biaxial orientation is ½ wavelength at a position of ± 40 degrees. .
[0067]
As mentioned above, although embodiment using a reflective circular polarizer was described, this embodiment is not limited above, Various changes are possible. For example, in the present invention, the retardation layer may be a ½ wavelength plate (also referred to as a ½ wavelength retardation plate) instead of the C plate. That is, the polarizing element of the present invention includes at least two layers of reflective circular polarizers and a half-wave plate disposed therebetween, and the two layers of reflective circular polarizers are selected in selective reflection of polarized light. A polarizing element in which at least part of the reflection wavelength band overlaps each other may be used. In this case, it is preferable that the rotational directions of the circularly polarized light transmitted through each of the two reflective circular polarizers are opposite to each other, and the oblique phase difference value of the ½ wavelength plate is 0 or λ. Ideal. When setting the phase difference value in the oblique direction, it is necessary to consider the phase difference value of the reflective circular polarizer as in the case of using the C plate. When a half-wave plate is used, anisotropy and coloring problems due to the azimuth angle of the tilting axis may occur. For example, for each of the two layers of the reflective circular polarizer and the retardation layer Coloring can be canceled by using layers having different wavelength dispersion characteristics.
[0068]
(Embodiment 2)
Next, another embodiment of the present invention will be described.
[0069]
In the polarizing element of the present invention, the reflective polarizer may be a reflective linear polarizer. More specifically, the polarizing element of the present invention includes at least two layers of reflective polarizers and an intermediate layer disposed between the two layers, and the two layers of reflective polarizers are orthogonal linearly polarized light. A reflective linear polarizer that selectively transmits one side and selectively reflects the other, wherein the two-layer reflective linear polarizers have at least a portion of the selective reflection wavelength bands in the selective reflection of polarized light overlapping each other; The layer is composed of one optical layer or includes a laminated structure of two or more optical layers, and the intermediate layer changes the polarization direction of incident linearly polarized light according to the incident direction. Alternatively, the two-layer reflective linear polarizer has a function of transmitting without changing the in-plane slow axis direction of the incident linearly polarized light from the direction perpendicular to the light incident surface (normal direction). Transmits incident light and applies incident light from an oblique direction. Angle may be a polarizing element that is arranged such that reflected manner.
[0070]
As such a polarizing element, for example, an element in which a C plate is sandwiched by a combination of a reflective linear polarizer and a ¼ wavelength plate (also referred to as a ¼ wavelength phase difference plate) is preferable. More specifically, it includes at least two reflective linear polarizers, a retardation layer disposed between them, and two quarter-wave plates, and one of the quarter-wave plates includes , One of the reflective linear polarizers is disposed between the retardation layer and the other quarter-wave plate is disposed between the other reflective linear polarizer and the retardation layer, In the two-layer reflective linear polarizer, at least a part of the selective reflection wavelength bands in the selective reflection of polarized light overlap each other, and the quarter-wave plate located on one surface side of the retardation layer has an in-plane retardation. The quarter wavelength plate located on the other surface side of the retardation layer has a phase axis that forms an angle of 40 ° to 50 ° with the polarization axis of the reflective linear polarizer located on the same side. The phase axis forms an angle of −40 ° to −50 ° with the polarization axis of the reflective linear polarizer located on the same side, and is 1/4 of the two layers. Plane angle between slow axis between the long plate is the polarizing element is preferably any. In this case, the retardation layer needs to satisfy the conditions of the following formulas (I) and (III).
[0071]
R ≦ (λ / 10) (I)
R ′ ≧ (λ / 4) (III)
[0072]
In formulas (I) and (III), the definitions of λ, R and R ′ are as described above.
[0073]
It has been found that a combination of a linear polarizer and a quarter wave plate can convert natural light into circularly polarized light. As shown in FIG. 3, when natural light 301 is incident on the linear polarizer 302, it is converted into linearly polarized light 303, and further, when the linearly polarized light 303 is passed through the ¼ wavelength plate 304, it is converted into circularly polarized light 305. The reflective circular polarizer and the reflective linear polarizer have an advantage that there is no dependency on the incident angle as compared with a prism-type reflective polarizer based on a principle such as the Brewster angle.
[0074]
If the C plate is simply sandwiched using a reflective linear polarizer, the optical axis for light rays incident on the C plate from an oblique direction is always orthogonal to the light beam direction, so that no phase difference is produced and polarization conversion is not performed. Therefore, the linearly polarized light is converted into circularly polarized light by a quarter wavelength plate having a slow axis direction at 45 ° or −45 ° with the polarization axis of the reflective linear polarizer, and then inverted by the phase difference of the C plate. What is necessary is just to convert into a polarized light and to convert the circularly polarized light into a linearly polarized light again with a quarter wavelength plate.
[0075]
The quarter wavelength plate and the half wavelength plate in the present invention are not particularly limited, and known ones can be used as appropriate. Specifically, for example, a uniaxially stretched or biaxially stretched polymer film, and a layer in which a liquid crystal compound is hybrid-aligned (an alignment state in which the plane direction is uniaxially aligned and further aligned in the thickness direction) are exemplified. The method for controlling the in-plane retardation and the thickness direction retardation in the quarter-wave plate and the half-wave plate is not particularly limited. For example, if it is a stretched polymer film, the stretching rate, the film thickness, etc. are adjusted. Can be controlled.
[0076]
The polymer that can be used for the polymer film is not particularly limited, but examples thereof include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, and acrylic polymers such as polymethyl methacrylate. , Styrene polymers such as polystyrene, acrylonitrile / styrene copolymer (AS resin), polycarbonate polymers such as bisphenol A / carbonic acid copolymer, linear or branched, such as polyethylene, polypropylene, ethylene / propylene copolymer Polyolefins containing cyclostructures such as polyolefin and polynorbornene, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers Polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers, and epoxy polymers. These may be used alone or in combination of two or more. Furthermore, an appropriate additive may be appropriately added to these polymer materials for any purpose such as imparting extensibility and shrinkage.
[0077]
The method for producing the polymer film is not particularly limited, and examples thereof include those produced by a casting method (extrusion molding method) and those produced by melting and forming the polymer material and then stretching, The latter is preferable from the viewpoint of mechanical strength and the like.
[0078]
Other examples of the polymer film include polymer films described in JP-A No. 2001-343529 (WO01 / 37007). Examples of the polymer film material include a resin containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain, and a thermoplastic resin having a substituted or unsubstituted phenyl group and cyano group in the side chain. The composition can be used, and examples thereof include a resin composition having an alternating copolymer composed of isobutene and N-methylenemaleimide and an acrylonitrile / styrene copolymer.
[0079]
Further, the reflective linear polarizer of the present invention is not particularly limited, and known ones can be used as appropriate. For example, stretched films having optical anisotropy or laminates thereof can be used, As the material of the stretched film, for example, the same materials as the quarter-wave plate and the half-wave plate can be used.
[0080]
FIG. 4 is a schematic diagram showing the polarizing element of the present embodiment. However, this embodiment is not limited to this. As shown in the figure, this polarizing element includes a reflective linear polarizer 404 (hereinafter also referred to as “layer 4”), a quarter-wave plate 405 (hereinafter also referred to as “layer 5”), and a C-plate 406 ( Hereinafter referred to as “layer 6”), a quarter-wave plate 407 (hereinafter sometimes referred to as “layer 7”), and a reflective linear polarizer 408 (hereinafter sometimes referred to as “layer 8”). Main components are laminated in this order, and light enters from the layer 4 side.
[0081]
FIG. 5 is a schematic diagram showing the bonding angle of each main component in the polarizing element of FIG. The angle formed by the polarization axis of the linear polarizer 404 and the in-plane slow axis of the quarter-wave plate 405 is 40 ° to 50 °, and the polarization axis of the linear polarizer 408 and the in-plane of the quarter-wave plate 407. The angle formed with the slow axis is −40 ° to −50 °. Other than this, the angle formed by each component is not particularly limited, and set 1 (combination of linear polarizer 404 and quarter-wave plate 405) and set 2 (linear polarizer 408) while maintaining the angle. And the quarter wave plate 407) can be rotated arbitrarily to achieve the same performance. For example, FIG. 14 is an example showing a case where the set 2 in the example shown in FIGS. 4 and 5 is rotated by 90 °, but the same performance as in FIGS. 4 and 5 can be exhibited even in this way. . Further, since the C plate does not have an optical axis in the plane, the bonding angle is arbitrary.
[0082]
Hereinafter, based on FIG. 4, an ideal operation principle when a light beam is incident on the polarizing element of the present embodiment will be described.
(1) First, natural light 14 is incident vertically from the backlight (light source) toward the reflective linear polarizer 404 (layer 4).
(2) The light 14 is separated into the linearly polarized light 15 and the linearly polarized light 16 orthogonal thereto, and the light 15 is transmitted through the layer 4 and the light 16 is reflected.
(3) The linearly polarized light 5 passes through the quarter-wave plate 405 (layer 5) and is converted into circularly polarized light 17.
(4) The circularly polarized light 17 does not change its polarization state, and passes through the C-plate 406 (layer 6) as the circularly polarized light 18.
(5) The circularly polarized light 18 passes through the quarter-wave plate 407 (layer 7) and is converted to linearly polarized light 19.
(6) The linearly polarized light 19 does not change its polarization state, and passes through the reflective linear polarizer 408 (layer 8) as the linearly polarized light 20.
(7) The linearly polarized light 20 enters the device (liquid crystal display device or the like) and is transmitted without loss.
(8) On the other hand, in addition to the natural light 14 from the vertical direction, natural light 21 from the oblique direction enters the layer 4 from the backlight.
(9) The light 21 is separated into the linearly polarized light 22 and the linearly polarized light 23 orthogonal thereto, and the light 22 is transmitted through the layer 4 (reflection linear polarizer), and the light 23 is reflected.
(10) The linearly polarized light 22 is transmitted through the layer 5 (¼ wavelength plate) and converted to circularly polarized light 24.
(11) When the circularly polarized light 24 passes through the layer 6 (C plate), the circularly polarized light 24 receives a phase difference of ½ wavelength, and the rotation direction is reversed to become the circularly polarized light 25.
(12) The circularly polarized light 25 is transmitted through the layer 7 (quarter wave plate) and converted into linearly polarized light 26.
(13) The linearly polarized light 26 is reflected by the layer 8 (reflective linear polarizer) and becomes the linearly polarized light 27.
(14) The linearly polarized light 28 is transmitted through the layer 7 (quarter wavelength plate) and converted to circularly polarized light 28.
(15) The circularly polarized light 28 receives a phase difference of ½ wavelength when passing through the layer 6 (C plate), and the rotational direction is reversed to become the circularly polarized light 29.
(16) The circularly polarized light 29 is transmitted through the layer 5 (quarter wave plate) and converted into linearly polarized light 30.
(17) The linearly polarized light 30 does not change its polarization state and passes through the layer 4 (reflection linear polarizer) as the linearly polarized light 31.
(18) The reflected lights 16, 23 and 31 are returned to the backlight side and recycled. The recycling mechanism is the same as in the first embodiment.
[0083]
In the present embodiment, the angle between the polarization axis of the reflective linear polarizer and the in-plane slow axis of the quarter-wave plate in the set 1 and set 2 (FIG. 5) is the ideal system theory. Above is 45 ° and -45 °. However, the characteristics of actual reflective polarizers and wave plates are not perfect in the visible light region, and there are subtle changes for each wavelength, which may cause problems such as coloring. Thus, if the color tone is compensated by slightly changing the angle and the entire system is rationally optimized, the problems such as coloring can be solved. Here, if the angle deviates greatly from 45 ° or −45 °, other problems such as a decrease in transmittance occur. Therefore, the adjustment is limited to within ± 5 °.
[0084]
The preferred range of the selective reflection wavelength band of the reflective linear polarizer is the same as that of the reflective circular polarizer. The point that the wavelength characteristic of transmitted light shifts to the short wavelength side with respect to the incident light in the oblique direction is the same as that of the reflective circular polarizer. It is preferable to have sufficient polarization characteristics and phase difference characteristics on the long wavelength side.
[0085]
Furthermore, if the preferable range of the oblique direction retardation value R ′ (formula (III)) in the retardation layer (C plate) of the present embodiment is also adjusted based on the same idea as in the case of using a reflective circular polarizer. good. However, since the reflective linear polarizer generally has a smaller phase difference characteristic than the reflective circular polarizer, the R ′ is required to be not less than 1/8 wavelength but not less than 1/4 wavelength.
[0086]
FIG. 15 shows the change of the polarization state by the quarter wavelength plate, the C plate and the quarter wavelength plate between the two reflective polarizers when obliquely incident light is incident on the polarizing element of FIG. Shown on the sphere. This figure shows a state in which the linearly polarized light incident from the first reflective polarizer is converted into the reverse linearly polarized light via the circularly polarized light. However, this figure is a reference material showing an example of the present invention, and does not limit the present invention.
[0087]
(Embodiment 3)
Next, still another embodiment of the present invention will be described.
[0088]
Instead of using a structure in which the C plate is sandwiched between two quarter-wave plates in the embodiment, the front phase difference (in-plane phase difference) is λ / 4, and the thickness direction phase difference is λ / 2 or more. A similar effect can be obtained by laminating two biaxial films that are perpendicular or parallel. In this case, the Nz coefficient (thickness direction retardation / in-plane retardation) satisfies the requirement if it is 2 or more.
[0089]
That is, the polarizing element of the present invention includes at least a two-layer reflective linear polarizer and a two-layer quarter-wave plate disposed between the two layers, and the two-layer reflective linear polarizer has a polarization selection function. At least some of the selective reflection wavelength bands in reflection overlap each other, and one in-plane slow axis of the quarter-wave plate is 40 ° to 50 ° with the polarization axis of the reflective linear polarizer located on the same side. Forming an angle, and the in-plane slow axis of the other quarter-wave plate forms an angle of −40 ° to −50 ° with the polarization axis of the reflective linear polarizer located on the same side. The angle formed by the in-plane slow axes of the four-wavelength plate is arbitrary, and each of the quarter-wave plates may be a polarizing element that satisfies the condition of the following formula (IV).
[0090]
Nz ≧ 2.0 (IV)
However, Nz = (nx−nz) / (nx−ny)
[0091]
In formula (IV):
nx, ny, and nz are refractive indexes in the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively, in the quarter-wave plate, and the X-axis direction is refracted in the plane of the quarter-wave plate. The direction in which the rate is maximum (in-plane slow axis direction), and the Y-axis direction is a direction perpendicular to the X-axis direction (in-plane fast axis direction) in the plane of the quarter-wave plate. The Z-axis direction is the thickness direction of the quarter-wave plate perpendicular to the X-axis direction and the Y-axis direction.
[0092]
The material of the quarter-wave plate and the reflective linear polarizer and the control method of the in-plane retardation and the thickness direction retardation are not particularly limited, and are as described in the second embodiment, for example.
[0093]
FIG. 6 is a schematic view showing the polarizing element of the present embodiment. However, this embodiment is not limited to this. As shown in the figure, this polarizing element includes a reflective linear polarizer 609 (hereinafter sometimes referred to as “layer 9”), a quarter wavelength plate 610 (hereinafter sometimes referred to as “layer 10”), a quarter wavelength. Main components of a plate 611 (hereinafter sometimes referred to as “layer 11”) and a reflective linear polarizer 612 (hereinafter sometimes referred to as “layer 12”) are laminated in this order, and the side of the layer 9 Light enters from.
[0094]
FIG. 7 is a schematic diagram showing a bonding angle of each main component in the polarizing element of FIG. The angle formed by the polarization axis of the linear polarizer 609 and the in-plane slow axis of the quarter-wave plate 610 is 40 ° to 50 °, and the polarization axis of the linear polarizer 612 and the in-plane of the quarter-wave plate 611. The angle formed with the slow axis is −40 ° to −50 °. Other than this, the angle formed by each component is not particularly limited, and set 1 (combination of linear polarizer 609 and quarter-wave plate 610) and set 2 (linear polarizer 612) while maintaining the angle. And the quarter wave plate 611) can be rotated arbitrarily to achieve the same performance. In FIGS. 6 and 7, for convenience of explanation, the upper and lower linear polarizer axes are parallel and the quarter wave plate axes are orthogonal to each other. However, the present invention is not limited to this.
[0095]
Hereinafter, based on FIG. 6, an ideal operation principle when natural light is incident on the polarizing element of the present embodiment will be described.
(1) First, natural light 32 is vertically incident from a backlight (light source).
(2) The natural light 32 is separated into the linearly polarized light 33 and the linearly polarized light 34 orthogonal thereto by the layer 9 (reflection linear polarizer). The linearly polarized light 33 is transmitted through the layer 9 and the linearly polarized light 34 is reflected.
(3) The linearly polarized light 33 is transmitted through the layer 10 and the layer 11 (¼ wavelength plate). In the example shown in this figure, since the in-plane slow axes of the layer 10 and the layer 11 are orthogonal, the front phase difference (in-plane phase difference) is 0 when considered as a combination of the layer 10 and the layer 11. It becomes. Therefore, the linearly polarized light 33 becomes the linearly polarized light 35 without changing its polarization state when passing through the layer 10 and the layer 11.
(4) The linearly polarized light 35 passes through the layer 12 (reflection linear polarizer) without changing its polarization state, and becomes linearly polarized light 36.
(5) The linearly polarized light 36 is transmitted without loss to the device (liquid crystal display device or the like).
(6) On the other hand, in addition to the natural light 32 that is vertically incident, natural light 37 that is obliquely incident is incident from the backlight.
(7) The natural light 37 is separated into the linearly polarized light 38 and the linearly polarized light 39 orthogonal thereto by the layer 9 (reflection linear polarizer), the linearly polarized light 38 is transmitted through the layer 9 and the linearly polarized light 39 is reflected.
(8) When the linearly polarized light 38 is obliquely incident on the layers 10 and 11 and passes through these layers, the polarization axis direction changes by 90 ° due to the influence of the thickness direction phase difference to become the linearly polarized light 40.
(9) The linearly polarized light 40 is incident on the layer 12 (reflection linear polarizer).
(10) Since layer 12 has the same axial direction as layer 9, linearly polarized light 40 is reflected by layer 12 to become linearly polarized light 41.
(11) When the linearly polarized light 41 passes through the layers 11 and 10, it is affected by the phase difference similarly to (9), and the polarization axis direction changes by 90 ° to become linearly polarized light 42.
(12) The linearly polarized light 42 passes through the layer 9 (reflection linear polarizer) without changing its polarization state, and becomes the linearly polarized light 43.
(13) The reflected lights 34, 39 and 43 are returned to the backlight side and recycled. The recycling mechanism is the same as in the first and second embodiments.
[0096]
The polarizing element of the present embodiment can exhibit the same performance as the polarizing element of the second embodiment, and the C plate can be omitted, so that the production efficiency is further superior to that of the polarizing element of the second embodiment. There is. The quarter-wave plate in the present embodiment is not particularly limited and is as described above. For example, a biaxially stretched polycarbonate (PC) or polyethylene terephthalate (PET) film, or a hybrid-aligned liquid crystal compound layer Is more preferable.
[0097]
The range of the angle between the reflective linear polarizer and the quarter-wave plate is as described above, and fine adjustment may be performed based on the same concept as in the second embodiment.
[0098]
The selective reflection wavelength band of the reflective linear polarizer is the same as in the first and second embodiments.
[0099]
Furthermore, in this embodiment, the utilization efficiency of oblique incident light changes by changing the value of Nz (formula (IV)), but the preferred range is not particularly limited, and is the same as in Embodiments 1 and 2. Adjustment may be made so as to obtain optimum light utilization efficiency based on the concept. The point which needs to consider the phase difference which a reflective polarizer has is the same as that of each said embodiment.
[0100]
(Embodiment 4)
Next, still another embodiment of the present invention will be described.
[0101]
Instead of using a structure in which the C plate is sandwiched between two quarter-wave plates in the second embodiment, the front phase difference (in-plane phase difference) is λ / 2, and the thickness direction phase difference is λ / 2. The same effect can be obtained by using a biaxial film as described above. In this case, the Nz coefficient needs to be 1.5 or more.
[0102]
That is, the polarizing element of the present invention includes at least two layers of reflective linear polarizers and a half-wave plate disposed therebetween, and the two layers of reflective linear polarizers are selected in selective reflection of polarized light. At least some of the reflection wavelength bands overlap each other, the in-plane slow axis of the half-wave plate forms an angle of 40 ° to 50 ° with the polarization axis of one of the reflective linear polarizers, and the other reflection A polarizing element having an angle of −40 ° to −50 ° with the polarization axis of the linear polarizer and satisfying the condition of the following formula (V) may be used.
[0103]
Nz ≧ 1.5 (V)
However, Nz = (nx−nz) / (nx−ny)
[0104]
In formula (V):
nx, ny, and nz are refractive indexes in the X-axis direction, the Y-axis direction, and the Z-axis direction of the half-wave plate, respectively, and the X-axis direction is refracted in the plane of the half-wave plate. The direction in which the rate is maximum (in-plane slow axis direction), and the Y-axis direction is a direction perpendicular to the X-axis direction (in-plane fast axis direction) in the plane of the half-wave plate The Z-axis direction is the thickness direction of the half-wave plate perpendicular to the X-axis direction and the Y-axis direction.
[0105]
The material and manufacturing method of the reflective linear polarizer and the wave plate are not particularly limited, and are the same as in the other embodiments.
[0106]
FIG. 8 is a schematic diagram showing the polarizing element of the present embodiment. However, this embodiment is not limited to this. As shown in the figure, this polarizing element includes a reflective linear polarizer 813 (hereinafter sometimes referred to as “layer 13”), a half-wave plate 814 (hereinafter sometimes referred to as “layer 14”), and a reflective linearly polarized light. Main components of the child 815 (hereinafter also referred to as “layer 15”) are stacked in this order, and light enters from the layer 13 side.
[0107]
FIG. 9 is a schematic diagram showing a bonding angle of each main component in the polarizing element of FIG. The angle formed by the polarization axis of the linear polarizer 813 and the in-plane slow axis of the half-wave plate 814 is 40 ° to 50 °, and the polarization axis of the linear polarizer 815 and the in-plane of the half-wave plate 814. The angle formed with the slow axis is −40 ° to −50 °. Accordingly, the in-plane slow axes of the two-layer linear polarizers are necessarily substantially orthogonal to each other.
[0108]
The polarizing element of the present embodiment can exhibit the same performance as the polarizing elements of Embodiments 2 and 3, and has an advantage that the production efficiency is further improved because the number of stacked layers is small.
[0109]
Hereinafter, based on FIG. 8, an ideal operation principle when natural light is incident on the polarizing element of the present embodiment will be described.
(1) First, natural light 47 is vertically incident from a backlight (light source).
(2) The natural light 47 is separated into the linearly polarized light 48 and the linearly polarized light 49 orthogonal thereto by the layer 13, the linearly polarized light 48 is transmitted through the layer 13, and the linearly polarized light 49 is reflected.
(3) When the linearly polarized light passes through the layer 14 (half-wave plate), it is affected by the front phase difference (in-plane phase difference), and the polarization axis direction is rotated by 90 ° to become the linearly polarized light 50.
(4) The linearly polarized light 50 passes through the layer 15 (reflection linear polarizer) without changing its polarization state, and becomes linearly polarized light 51.
(5) The transmitted linearly polarized light 51 is transmitted to the device (liquid crystal display device or the like) without loss.
(6) On the other hand, in addition to the natural light 47 incident vertically, natural light 52 incident obliquely is incident from the backlight.
(7) The natural light 52 is separated into the linearly polarized light 53 and the linearly polarized light 54 orthogonal thereto by the layer 13 (reflection linear polarizer). The linearly polarized light 53 is transmitted through the layer 13 and the linearly polarized light 54 is reflected.
(8) The linearly polarized light 53 is obliquely incident on the layer 14 (half-wave plate) and is transmitted as the linearly polarized light 55 without changing the polarization axis direction.
(9) The linearly polarized light 55 is reflected by the layer 15 (reflective linear polarizer) and becomes the linearly polarized light 56.
(10) The linearly polarized light 56 is incident on the layer 14 and is transmitted without changing the polarization axis direction to become the linearly polarized light 57.
(11) The transmitted linearly polarized light 57 passes through the layer 13 without changing its polarization state and becomes linearly polarized light 58.
(12) The reflected lights 49, 54 and 58 are returned to the backlight side and recycled. The recycling mechanism is the same as in the other embodiments.
[0110]
The range of the angle formed by the reflective linear polarizer and the half-wave plate is as described above, and fine adjustment thereof may be performed based on the same concept as in the second and third embodiments.
[0111]
The selective reflection wavelength band of the reflective linear polarizer is the same as in the first to third embodiments.
[0112]
Furthermore, in this embodiment, the utilization efficiency of oblique incident light changes by changing the value of Nz (formula (V)), but the preferred range is not particularly limited, and is the same as in Embodiments 1 to 3. Adjustment may be made so as to obtain optimum light utilization efficiency based on the concept. The point which needs to consider the phase difference which a reflective polarizer has is the same as that of each said embodiment.
[0113]
As mentioned above, although this invention was demonstrated based on Embodiment 1-4, this invention is not limited to said description, All the changes are possible in the range which does not deviate from the main point. For example, the polarizing element of the present invention may appropriately include other optical layers and other components as long as the object can be achieved, in addition to the components described above.
[0114]
(Manufacturing method etc.)
Next, the manufacturing method of the polarizing element of this invention is demonstrated. First, the material and manufacturing method of each component such as the C plate, the reflective polarizer, and the wave plate are as described above.
[0115]
Although the manufacturing method of the polarizing element of this invention is not specifically limited, It can manufacture by laminating | stacking said each component and another component as needed. The form of lamination is not particularly limited, and each component may be simply stacked. However, from the viewpoint of workability and light utilization efficiency, each component is made of a light-transmitting adhesive or pressure-sensitive adhesive. It is preferable that the layers are stacked via layers. In the present invention, although there is no clear distinction between “adhesive” and “adhesive”, an adhesive that is relatively easy to peel or re-adhere is called “adhesive” for convenience.
[0116]
The adhesive or the pressure-sensitive adhesive is not particularly limited, but is preferably transparent and has no absorption in the visible light region, and the refractive index is as close as possible to the refractive index of each layer, from the viewpoint of suppressing surface reflection. Therefore, for example, acrylic, epoxy, and isocyanate adhesives and pressure-sensitive adhesives can be preferably used. In addition to the solvent type, these adhesives and pressure-sensitive adhesives can be appropriately used, for example, an ultraviolet polymerization type, a thermal polymerization type, and a two-component mixing type. The method for laminating each component is not particularly limited, and any method suitable for these properties may be used. For example, monodomains can be formed separately on an alignment film or the like, and sequentially laminated by a method such as transferring to a translucent substrate.
[0117]
When each component is a layer containing a liquid crystal compound, etc., instead of using an adhesive or pressure-sensitive adhesive layer, an alignment film or the like is appropriately formed, and the respective components are sequentially formed directly (direct continuous coating). ) Etc. are also possible. This method is advantageous from the viewpoint of reducing the thickness of the polarizing element. When a reflective circular polarizer and a C plate are used, each component does not have an in-plane optical axis, and the bonding angle is arbitrary, so that bonding by the roll-to-roll method or the direct continuous coating is performed. This has the advantage that it can be manufactured and the productivity is high.
[0118]
Moreover, you may add various additives etc. to the said each component and adhesive bond layer (adhesive layer) as needed. For example, particles may be added to adjust the degree of diffusion to impart isotropic scattering, or a surfactant may be added as appropriate for the purpose of imparting leveling properties during film formation. Further, an ultraviolet absorber or an antioxidant may be added as appropriate.
[0119]
(Polarized light source and image display device)
Next, a polarized light source and an image display device using the polarizing element of the present invention will be described.
[0120]
First, a polarized light source (polarized light source device) of the present invention includes a light source, a reflective layer, and the polarizing element of the present invention, and the polarized light is laminated on the light source via the reflective layer. Light source. Although the manufacturing method of a polarized light source is not specifically limited, For example, the method etc. which are described in Unexamined-Japanese-Patent No. 10-321025 etc. are employable.
[0121]
The image display device of the present invention is an image display device including the polarizing element of the present invention. The image display device using the polarizing element or the polarized light source of the present invention is not particularly limited, and can be preferably used for an image display device such as an organic EL display device, PDP, CRT, etc., but is particularly preferably used for a liquid crystal display device. be able to.
[0122]
Hereinafter, the liquid crystal display device of the present invention will be described.
[0123]
The liquid crystal display device of the present invention is a liquid crystal display device comprising the polarized light source of the present invention, and further having a liquid crystal cell laminated on the polarizing element. Other than this, the configuration and manufacturing method of the liquid crystal display device of the present invention are not particularly limited, and known configurations and manufacturing methods can be used as appropriate. The polarized light source of the present invention is excellent in light utilization efficiency, bright, excellent in the perpendicularity of emitted light, provides light without unevenness in brightness and darkness, and can be easily enlarged. It can be preferably used for forming a device, and can be particularly preferably used for a direct-view type liquid crystal display device.
[0124]
There is no particular limitation on the liquid crystal cell used in the liquid crystal display device of the present invention, and an appropriate one can be used. Among them, a liquid crystal cell that performs display by entering light in a polarized state is suitable. For example, a liquid crystal cell using a twisted nematic liquid crystal or a super twisted nematic liquid crystal is preferable. However, the liquid crystal cell is not limited thereto, and a non-twist liquid crystal, a guest-host liquid crystal in which a dichroic dye is dispersed in the liquid crystal, a ferroelectric liquid crystal, or the like is also suitable. There is no particular limitation on the driving method of the liquid crystal.
[0125]
Furthermore, constituent elements other than the liquid crystal cell are not particularly limited, and a known member for a liquid crystal display device or the like can be appropriately used. For example, appropriate optical layers such as a diffusion plate, an antiglare layer, an antireflection film, a protective layer, a protective plate, and a compensation retardation plate provided between the liquid crystal cell and the polarizing plate are appropriately disposed on the polarizing plate on the viewing side. can do.
[0126]
Next, the organic electroluminescence device (organic EL display device) of the present invention will be described.
[0127]
The polarizing element and the polarized light source of the present invention can be used in any image display device other than the liquid crystal display device, but are suitable for an organic EL display device, for example. The organic EL display device of the present invention is not particularly limited except that the polarizing element or polarized light source of the present invention is used, and a known configuration and manufacturing method can be applied. Hereinafter, the organic EL display device will be described, but this description does not limit the present invention.
[0128]
Generally, in an organic EL display device, a transparent electrode, an organic light emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitter (organic electroluminescent light emitter). Here, the organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative and the like and a light emitting layer made of a fluorescent organic solid such as anthracene, or Structures having various combinations such as a laminate of an electron injection layer composed of such a light emitting layer and a perylene derivative or a hole injection layer and a laminate of a light emitting layer and an electron injection layer are known. Yes.
[0129]
The light emission principle of the organic EL display device is as follows. That is, first, holes and electrons are injected into the organic light emitting layer by applying a voltage to the transparent electrode and the metal electrode. The energy generated by the recombination of these holes and electrons excites the fluorescent material, and emits light on the principle that light is emitted when the excited fluorescent material returns to the ground state. The mechanism of recombination in the middle is the same as that of a general diode, and as can be predicted from this, the current and the emission intensity show strong nonlinearity with rectification with respect to the applied voltage.
[0130]
In an organic EL display device, in order to extract light emitted from the organic light emitting layer, at least one of the electrodes must be transparent, and a transparent electrode usually formed of a transparent conductor such as indium tin oxide (ITO) is used as an anode. It is used as. On the other hand, in order to facilitate electron injection and increase luminous efficiency, it is important to use a material having a small work function for the cathode, and usually metal electrodes such as Mg—Ag and Al—Li are used.
[0131]
In the organic EL display device having such a configuration, the organic light emitting layer is formed of a very thin film having a thickness of about 10 nm. For this reason, the organic light emitting layer transmits light almost completely like the transparent electrode. As a result, light that is incident from the surface of the transparent substrate at the time of non-light emission, passes through the transparent electrode and the organic light emitting layer, and is reflected by the metal electrode is again emitted to the surface side of the transparent substrate. The display surface of the organic EL display device looks like a mirror surface.
[0132]
As described above, an organic EL display device generally includes a transparent electrode on the front side of an organic light emitting layer that emits light when a voltage is applied, and a metal electrode on the back side, and the organic light emitting layer, the transparent electrode, and the metal electrode are provided. Together, it forms an organic electroluminescent light emitter. In such an organic EL display device, a polarizing plate can be provided on the surface side of the transparent electrode, and a retardation plate can be provided between the transparent electrode and the polarizing plate.
[0133]
Since the retardation plate and the polarizing plate have a function of polarizing light incident from the outside and reflected by the metal electrode, there is an effect that the mirror surface of the metal electrode is not visually recognized by the polarization action. In particular, the mirror surface of the metal electrode can be completely shielded by configuring the retardation plate with a quarter-wave plate and adjusting the angle formed by the polarization direction of the polarizing plate and the retardation plate to π / 4. .
[0134]
That is, only the linearly polarized light component of the external light incident on the organic EL display device is transmitted by the polarizing plate. This linearly polarized light becomes generally elliptically polarized light by the retardation plate, but becomes circularly polarized light particularly when the retardation plate is a quarter wavelength plate and the angle formed by the polarization direction of the polarizing plate and the retardation plate is π / 4. .
[0135]
This circularly polarized light is transmitted through the transparent substrate, the transparent electrode, and the organic thin film, is reflected by the metal electrode, is again transmitted through the organic thin film, the transparent electrode, and the transparent substrate, and becomes linearly polarized light again on the retardation plate. And since this linearly polarized light is orthogonal to the polarization direction of a polarizing plate, it cannot permeate | transmit a polarizing plate. As a result, the mirror surface of the metal electrode can be completely shielded.
[0136]
The polarization light source and the image display apparatus using the polarization element of the present invention have been described above, but the present invention is not limited to the above description. The polarizing element of the present invention exhibits the effect that only the light in the front direction is transmitted and the light in the oblique direction is cut by reflection when the reflective polarizer and the retardation layer used satisfy the requirements of the present invention. it can. Further, by adjusting the selective reflection wavelength band of the reflective polarizer, the above effect can be exerted with less wavelength dependency in a wide wavelength region. Furthermore, since it has less dependency on the characteristics of the light source than the collimation and condensing system by the combination of the interference filter of the prior art and the emission light source, it can be used for any polarized light source and image display device.
[0137]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited only to the following Examples.
[0138]
(Measurement equipment, etc.)
The equipment used in the examples and comparative examples is as follows. That is, various cold cathode tubes CCFL manufactured by Elevam were used as the cold cathode tubes. As the backlight, various backlights of Stanley Electric Co. and Tama Electric Industry Co., Ltd. were used. A light table manufactured by HAKUBA was used.
The following measuring equipment was used.
(1) For selective reflection wavelength band measurement, MCPD2000 (trade name), which is an instantaneous multi-photometry system manufactured by Otsuka Electronics, was used.
(2) For the haze measurement, HM150 (trade name), which is a haze meter made by Murakami Color, was used.
(3) U4100 (trade name), which is a spectrophotometer manufactured by Hitachi, Ltd., was used for measuring the spectral characteristics of transmission and reflection.
(4) DOT3 (trade name) manufactured by Murakami Color was used to measure the characteristics of the polarizing plate.
(5) KOBRA21D (trade name), which is a birefringence measuring device of Oji Scientific Instruments, was used for phase difference measurement of a phase difference plate or the like.
(6) For luminance measurement, BM7 (trade name), which is a luminance meter made by Topcon, was used.
[0139]
(Example 1)
A polarizing element including a reflective circular polarizer and a negative C plate was produced as follows, and the characteristics were examined.
[0140]
That is, first, a reflective polarizer (reflective circular polarizer) including a cholesteric liquid crystal layer was prepared using a commercially available polymerizable nematic liquid crystal monomer (polymerizable mesogen compound) and a chiral agent. These types and mixing ratios were selected so that the center value of the selective reflection wavelength band of the completed cholesteric liquid crystal layer was 550 nm and the width was about 60 nm. Specifically, BASF LC242 (trade name) was used as the polymerizable mesogenic compound, and BASF LC756 (trade name) was used as the polymerizable chiral agent, and the mixing ratio was as follows.
Mesogenic compound: chiral agent = 4.9: 95.1 (weight ratio)
[0141]
The specific operation for producing the reflective circular polarizer is as follows. That is, first, a mixture of the polymerizable chiral agent and the polymerizable mesogenic compound was dissolved in cyclopentane, and the solute concentration was adjusted to 20 wt%. Further, 1 wt% of a reaction initiator (manufactured by Ciba-Gaigi, Irg907 (trade name)) was added to the solution to prepare a coating solution.
[0142]
On the other hand, a PET film (manufactured by Toray, Lumirror (trade name), thickness 75 μm) was prepared, and the surface thereof was subjected to an alignment treatment with a rubbing cloth to obtain an alignment substrate. Next, the coating solution was applied with a wire bar onto the alignment-treated surface of the alignment substrate. The amount of the solution applied at this time was adjusted so that the thickness after drying was 5 μm. This was dried at 90 ° C. for 2 minutes, further heated to an isotropic transition temperature of 130 ° C. of the liquid crystal, and then gradually cooled to maintain a uniform alignment state. And it hardened | cured by ultraviolet irradiation (10 mW / square cm x 1 minute) at 80 degreeC, and the reflective polarizer layer A containing a cholesteric liquid crystal compound was obtained. Further, a glass plate is prepared, and a light-transmitting isocyanate-based adhesive (made by Special Colorant Industries Co., Ltd., AD249 (trade name)) is applied to a thickness of 5 μm, and the reflective polarizer layer is formed on the coated surface. A was transferred to obtain the desired reflective circular polarizer. When the selective reflection wavelength band of this reflective circular polarizer was measured, a designed value of 520 to 580 nm was obtained.
[0143]
Next, a negative C plate layer containing a polymerized liquid crystal compound was prepared so that the center value of the cholesteric selective reflection wavelength band was 350 nm. Specifically, BASF LC242 (trade name) was used as the polymerizable mesogenic compound, and BASF LC756 (trade name) was used as the polymerizable chiral agent, and the mixing ratio was as follows.
Mesogenic compound: chiral agent = 11.0: 88.0 (weight ratio)
[0144]
The specific operation for producing the negative C plate layer is as follows. That is, first, a mixture of the polymerizable chiral agent and the polymerizable mesogenic compound was dissolved in cyclopentane, and the solute concentration was adjusted to 30 wt%. Furthermore, 1 wt% of a reaction initiator (manufactured by Ciba-Gaigi, Irg907 (trade name)) and 0.013 wt% of a surfactant (manufactured by Big Chemi Japan, BYK-361 (trade name)) were added to this solution.
[0145]
On the other hand, a PET film (manufactured by Toray, Lumirror (trade name), thickness 75 μm) was prepared, and the surface thereof was subjected to an alignment treatment with a rubbing cloth to obtain an alignment substrate. Next, the coating solution was applied with a wire bar onto the alignment-treated surface of the alignment substrate. The amount of the solution applied at this time was adjusted so that the thickness after drying was 6 μm. This was dried at 90 ° C. for 2 minutes, further heated to an isotropic transition temperature of 130 ° C. of the liquid crystal, and then gradually cooled to maintain a uniform alignment state. And it hardened | cured by ultraviolet irradiation (10 mW / square cm x 1 minute) at 80 degreeC, and obtained the laminated body in which the target negative C plate layer containing a cholesteric liquid crystal compound was formed on the said alignment substrate.
[0146]
When the retardation of this negative C plate layer was measured, it was 2 nm in the front direction (in-plane retardation) with respect to light having a wavelength of 550 nm (a value that can be regarded as substantially 0), and was inclined by 30 °. The phase difference was 160 nm (> λ / 8).
[0147]
Furthermore, a polarizing element was produced using the obtained reflective circular polarizer and negative C plate layer. That is, first, the reflective circular polarizer in which the reflective circular polarizer layer A was laminated on the glass plate was prepared. Next, the negative C plate layer was transferred onto the reflective circular polarizer layer A. That is, a translucent adhesive (AD249 (trade name) manufactured by Special Colorant Industries Co., Ltd.) is applied to the reflective circular polarizer layer A to a thickness of 5 μm, and the alignment substrate (PET film) is further formed thereon. The negative C plate layer formed above was adhered, and the alignment substrate was peeled off, leaving only the negative C plate layer. Further, another reflective circular polarizer layer A was transferred onto the negative C plate layer in the same manner to obtain a target polarizing element. In this polarizing element, a first reflective circular polarizer layer A, a negative C plate layer, and a second reflective circular polarizer layer A are laminated in this order on a glass plate. It is bonded via an adhesive layer.
[0148]
Next, the performance of the obtained polarizing element was evaluated. That is, first, a polarized light source was prepared by combining the polarizing element with a green diffused light source having a bright line at 544 nm. Specifically, a G0 type cold cathode tube made of Elevum and a light scattering plate (haze 90% or more) are combined to form a diffused light source, and further, the polarizing element is combined to form a polarized light source, which is used in a direct type backlight device. Arranged. The light scattering plate was disposed between the polarizing element and the cold cathode tube.
[0149]
When the characteristics of the polarized light source were examined, a light beam was emitted in the normal direction, but the transmitted light beam decreased at an angle of 30 ° or more and almost no light beam was emitted at an angle of around 45 °. FIG. 16 also shows the relationship between the emission angle of the emitted light beam and the relative luminance when the diffused light source alone is used and when the polarizing element of this embodiment is combined to form a polarized light source.
[0150]
It can be seen from FIG. 16 that according to the polarizing element of this example, light can be efficiently condensed in the front direction. Unlike a sidelight-type backlight, it is generally difficult to condense with a lens or prism in the front direction with a direct-type backlight, so this can be said to be a feature of the polarizing element.
[0151]
Next, the polarizing element of this example was placed on a backlight for a liquid crystal display device (manufactured by Stanley Electric Co., Ltd., sidelight / wedge type backlight) using a three-wavelength cold cathode tube, and the characteristics thereof were evaluated. In this case as well, a light beam was emitted in the normal direction, but the transmitted light beam decreased at an angle of 30 ° or more. Since the polarizing element does not support the entire visible light range, blue (435 nm) and red (610 nm) can be extracted without narrowing the angle, but the spectrum of green (545 nm), which has the highest visibility, can be cut. The function as a device was confirmed.
[0152]
(Example 2)
A polarizing element was produced in the same manner as in Example 1 except that a positive C plate layer was used instead of the negative C plate layer, and the performance was evaluated. That is, first, a positive C plate layer containing a polymerized liquid crystal compound was prepared using a liquid crystal monomer represented by the following structural formula (referred to as polymerizable nematic monomer A).
[Chemical 1]

[0153]
The specific operation for producing the positive C plate layer is as follows. That is, first, the polymerizable nematic monomer A was dissolved in cyclopentane, and the solute concentration was adjusted to 30 wt%. Further, 1 wt% of a reaction initiator (manufactured by Ciba-Gaigi, Irg907 (trade name)) was added to this solution to prepare a coating solution. On the other hand, a PET film (manufactured by Toray, Lumirror (trade name), thickness 75 μm) is prepared, and a cyclohexane solution (0.1 wt%) of a mold release treatment agent (octadecyltrimethoxysilane) is thinly applied thereon and dried. A vertical alignment film was formed to obtain an alignment substrate. And the said coating solution was apply | coated with the wire bar on the vertical alignment film formation surface of this alignment substrate. The amount of the solution applied at this time was adjusted so that the thickness after drying was 2 μm. This was dried at 90 ° C. for 2 minutes, further heated to an isotropic transition temperature of 130 ° C. of the liquid crystal, and then gradually cooled to maintain a uniform alignment state. And it hardened | cured by ultraviolet irradiation (10 mW / square cm x 1 minute) at 80 degreeC, and obtained the laminated body by which the target positive C plate layer was formed on the said alignment substrate. When the phase difference of this positive C plate was measured, the phase difference when measured at an inclination of 0 nm and 30 ° with respect to light having a wavelength of 550 nm was about 170 nm (> λ / 8).
[0154]
Further, a polarizing element was obtained in the same manner as in Example 1 except that this positive C plate was used in place of the negative C plate layer of Example 1. When the performance was evaluated using the obtained polarizing element in the same manner as in Example 1, it was almost the same as in Example 1.
[0155]
(Example 3)
A polarizing element including a reflective linear polarizer, a quarter-wave plate, and a C plate was produced as follows, and the performance was evaluated.
[0156]
First, a reflective linear polarizer was produced. That is, first, 20 layers are stacked by alternately stacking thin films while controlling the thickness by a feed block method so that polyethylene naphthalate (PEN) and naphthalenedicarboxylic acid-terephthalic acid copolyester (co-PEN) are alternately stacked. A multilayer film was obtained. Furthermore, this multilayer film was uniaxially stretched. The stretching temperature at this time was about 140 degrees, and the stretching ratio was about 3 times in the TD direction. The thickness of each thin layer in the stretched film thus obtained was about 0.1 μm. Five sheets of the 20-layer laminated film stretched product were further laminated to obtain a target reflective linear polarizer (reflective polarizer B) as a total of 100 laminated products. The reflective polarizer B has a reflection function for linearly polarized light in a wavelength band of 500 nm or more and 600 nm or less depending on the overall reflectance.
[0157]
Further, a polarizing element was produced using the reflective polarizer B. That is, first, a negative C plate layer was prepared in the same manner as in Example 1, and a quarter-wave retardation plate (Nitto Denko, NRF film (trade name) made of polycarbonate uniaxially stretched film on both sides thereof at 550 nm. A retardation (in-plane retardation) of 135 nm) was adhered, and a reflective polarizer B was adhered to the outside thereof to obtain a target polarizing element. The laminating angle of each layer is such that the transmission polarization axis direction of the reflective polarizer B on the incident side is 0 °, the in-plane slow axis direction of the quarter-wave plate on the incident side is 45 °, the C plate has no axial orientation, Bonding was performed so that the in-plane slow axis direction of the exit-side ¼ plate was −45 ° and the transmission polarization axis direction of the exit-side polarizer was 90 °. The adhesion of each layer was performed by applying an acrylic pressure-sensitive adhesive (Nitto Denko No. 7) to a thickness of 25 μm between each layer, and the alignment substrate was peeled off from the negative C plate layer, and only the liquid crystal-containing layer was used. . When the performance was evaluated using the obtained polarizing element in the same manner as in Example 1, it was almost the same as in Example 1.
[0158]
(Example 4)
In the following manner, a polarizing element including a reflective linear polarizer and a half-wave retardation plate was produced, and its performance was evaluated. That is, first, two reflective polarizers B produced in the same manner as in Example 3, and a front phase difference of 270 nm (measurement wavelength 550 nm) obtained by biaxially stretching a polycarbonate film (manufactured by Kaneka Chemical), Nz A retardation film (1/2 wavelength plate) having a coefficient of 2.0 was prepared. Then, these layers were bonded in an arrangement in which the half-wave plate was sandwiched between the two reflective polarizers B to obtain a target polarizing element. The laminating angle of each layer is such that the transmission polarization axis direction of the reflective polarizer B on the incident side is 0 °, the in-plane slow axis direction of the half-wave plate is 45 °, and the transmission polarization axis direction of the output side polarizer is Was laminated so as to be 90 °. Adhesion of each layer was performed by applying an acrylic pressure-sensitive adhesive (Nitto Denko No. 7) to each layer to a thickness of 25 μm. When this polarizing element was evaluated in the same manner as in Example 3, it was found that it had the same performance as in Example 3.
[0159]
(Example 5)
A reflective circular polarizer (broadband reflective circular polarizer) having a selective reflection wavelength band in a wide wavelength region was produced as follows, and a polarizing element was produced using the same and a C plate to evaluate the performance. .
[0160]
First, a broadband reflective circular polarizer was fabricated. That is, first, a nematic monomer A (similar to the above) and a chiral monomer B represented by the following structural formula were prepared.
[Chemical 2]

[Chemical Formula 3]

[0161]
Next, the nematic monomer A and the chiral monomer B were mixed and polymerized at a predetermined ratio, and a cholesteric liquid crystal layer was produced using the mixture. Further, four cholesteric liquid crystal layers having different selective reflection wavelength bands were prepared by changing the mixing ratio of the nematic monomer A and the chiral monomer B. In the production, reference was made to European Patent Application No. 0837544. Specifically, it is as follows.
[0162]
First, the mixing ratio (weight ratio) of the nematic monomer A and the chiral monomer B, the selective reflection wavelength band of each cholesteric liquid crystal layer and the center wavelength calculated from the mixing ratio are shown in Table 1 below.

[0163]
Next, nematic monomer A and chiral monomer B were polymerized to synthesize a cholesteric liquid crystal compound. That is, first, the mixture having each composition shown in Table 1 was made into a 33 wt% tetrahydrofuran solution, and 0.5 wt% of a reaction initiator (azobisisobutyronitrile) was further added. This was purged with nitrogen at 60 ° C. and then polymerized by a conventional method, and the product was reprecipitated and separated with diethyl ether and purified to obtain the desired cholesteric liquid crystal compound.
[0164]
On the other hand, an 80 μm-thick triacetyl cellulose (TAC) film (manufactured by Fuji Photo Film Industry, TD-TAC (trade name)) was prepared, and a polyimide layer having a thickness of about 0.1 μm was applied to the surface. The surface was rubbed with a rayon rubbing cloth to obtain an alignment substrate. Next, a 10 wt% methylene chloride solution of the cholesteric liquid crystal compound was applied on the rubbing surface so that the thickness after drying with a wire bar was 1.5 μm. This was heat-treated at 140 ° C. for 15 minutes, and then allowed to cool at room temperature to fix the alignment state of the cholesteric liquid crystal compound to obtain a cholesteric liquid crystal layer. Each of the synthesized cholesteric liquid crystal compounds was subjected to the above operation to obtain cholesteric liquid crystal layers having respective selective reflection wavelength bands shown in Table 1.
[0165]
Then, the obtained four cholesteric liquid crystal layers were bonded in order from the short wavelength side to obtain a liquid crystal composite layer having a thickness of about 10 μm to obtain a desired broadband reflective circular polarizer. Adhesion was sequentially performed by a method in which a transparent isocyanate-based adhesive (manufactured by Special Colorant Industries, AD244 (trade name)) was applied to the surface of each liquid crystal layer, and one side of the alignment substrate (TAC film) was peeled off after adhesion. When the selective reflection function of the obtained broadband reflective circular polarizer was measured, it was found to have a selective reflection function at 430 nm to 710 nm.
[0166]
Then, a C plate layer was produced in the same manner as in Example 1, and the broadband reflective circular polarizer was adhered to both sides thereof to obtain a target polarizing element. Adhesion was performed in the same manner as in Example 1 by applying a light-transmitting pressure-sensitive adhesive (Nitto Denko No. 7) to each layer in a thickness of 25 μm. The rotational directions of the circularly polarized light that is transmitted (reflected) between the upper and lower reflective circular polarizers are the same.
[0167]
Next, the performance of the polarizing element of this example was evaluated by the same method as in Example 1. In the evaluation using the green diffused light source, it was confirmed that the light collecting performance was the same as that of the polarizing element of Example 1. In addition, evaluation by a backlight for a liquid crystal display device using a three-wavelength cold cathode tube also showed excellent light collecting performance as in Example 1. However, the polarizing element of this example has the same light collecting performance in the entire visible light region. It turned out that it is further superior to the polarizing element of Example 1 at the point which exhibits optical performance.
[0168]
Furthermore, the polarizing element of this example was placed on another backlight (a direct type backlight using a cold cathode tube, manufactured by Tama Electric Industry Co., Ltd.), and the light collecting performance was evaluated. In this case as well, a light beam was emitted in the normal direction, but the transmitted light beam decreased at an angle of 30 ° or more. And it turned out that the same condensing performance is exhibited in visible light whole region.
[0169]
(Example 6)
A polarizing element was produced in the same manner as in Example 5 except that the thickness and retardation value of the C plate layer were changed, and the light collecting performance was evaluated in the same manner as in Example 5. In this example, the thickness of the C plate was 4 μm, and the phase difference was measured. As a result, the front phase difference was 1 nm and the phase difference at 30 ° inclination was 100 nm (> λ / 8).
[0170]
FIG. 16 shows the relationship between the emission angle of the emitted light beam and the relative luminance when the polarizing element of Examples 5 and 6 is combined with a diffusing light source to form a polarized light source, and when only the diffusing light source is used. Show. From this figure, it can be seen that although all the polarizing elements show excellent light collecting performance, Example 5 has a sharper light collecting angle and a larger front luminance increase.
[0171]
(Example 7)
The polarizing element of Example 5 was incorporated into a liquid crystal display device, and the display performance was evaluated. Specifically, it is as follows. First, as a liquid crystal display device, a TFT liquid crystal display device (diagonal 11.3 inches) obtained from Dynabook SS3430 (trade name) manufactured by Toshiba was prepared. This device is a type that uses a light source of a side light type light guide and condenses it in front by a prism sheet. Next, the prism sheet is removed from the liquid crystal display device, and a quarter wavelength plate (NRF-140 (trade name) manufactured by Nitto Denko) is attached to the polarizer on the back side of the device at an angle of 45 ° to the polarization axis. Further, the polarizing element obtained in Example 5 was adhered thereon. Adhesion was performed by applying a translucent adhesive (Nitto Denko No. 7) to a thickness of 25 μm. Thus, the commercially available liquid crystal display device was processed, and the target liquid crystal display device incorporating the polarizing element of Example 5 was obtained. When the performance of the obtained liquid crystal display device with a polarizing element was compared with that before processing (when using a prism sheet), the light condensing characteristics to the front were the same as when using the prism sheet, and the front luminance was higher than before processing. It was found that it was improved by 20%. This result shows the superiority of the polarizing element of the present invention over the prior art such as a prism sheet.
[0172]
(Comparative Example 1)
A polarizing element was produced in the same manner as in Example 1, except that the C plate layer was not used and two layers of reflective circular polarizers were directly bonded. When the performance of this polarizing element was evaluated, it was possible to obtain only the same optical function as that of a single reflective circular polarizer, and phenomena such as selective improvement in reflectance and reduction in transmittance were observed in the oblique direction. There wasn't.
[0173]
(Comparative Example 2)
A polarizing element was produced in the same manner as in Example 1 except that a quarter wavelength plate was used instead of the C plate layer. As the ¼ wavelength plate, an A plate (NRF-140 film (trade name) manufactured by Nitto Denko Corporation, thickness 50 μm) having a front retardation λ / 4 and an Nz coefficient = 1.0 made of a stretched film of a polycarbonate film is used. Using. When the performance of the obtained polarizing element was evaluated, the front transmittance was reduced to about ½ compared to Example 1, and the transmittance in the oblique incident direction was not lowered, and the functions of condensing and collimating were as follows. I didn't have it.
[0174]
(Comparative Example 3)
A polarizing element was obtained in the same manner as in Example 3, except that a commercially available iodine-based absorption dichroic polarizer (manufactured by Nitto Denko, NPF-EG1425DU (trade name)) was used instead of the reflective polarizer B. When the performance of this polarizing element was evaluated, the effect of limiting the viewing angle by the transmission characteristic in the front direction and the absorption characteristic in the oblique direction was obtained, but the absorption loss was significant and the front brightness was not improved.
[0175]
(Luminance evaluation using a light table)
Each polarizing element of Examples 1-6 and Comparative Examples 1-3 is arrange | positioned on a commercially available light table (the product made by Hakuba, 3 wavelength fluorescent lamp, direct type diffused light source), and the brightness | luminance (2 degree visual field) in the perpendicular upper direction is arranged. It measured using the luminance meter (the Topcon make, BM7 (brand name)). The measured value was normalized with the value measured with only the light table as 100. The measurement results are shown in Table 2.
[0176]
(Table 2)
Relative brightness
Example 1 80
Example 2 78
Example 3 72
Example 4 70
Example 5 82
Example 6 90
Comparative Example 1 67
Comparative Example 2 21
Comparative Example 3 39
[0177]
As can be seen from Table 2, the polarizing element of the example showed an excellent luminance improvement effect with respect to the front direction even when used in a light table. In addition, as shown in FIGS. 16 and 17, the polarizing element of the example has a front relative luminance of more than 100 (the front luminance of the original backlight) when used in a direct type backlight for a liquid crystal display device. However, the relative luminance in Table 2 was slightly less than 100. This is because the efficiency of the return light reflected by the reflective polarizer returning to the normal direction is slightly worse in the commercial light table than in the case of the direct type backlight. However, it can be seen that it has a remarkably superior brightness enhancement effect in the front direction as compared with the polarizing element of the comparative example.
[0178]
【The invention's effect】
  As described above, according to the polarizing element of the present invention, the obliquely transmitted light is efficiently reflected to the light source side without impairing the transmission polarization characteristics of the normal incident light that contributes to the front luminance.it can. Further, it is possible to further improve the luminance by converting the obliquely transmitted light (reflected polarized light) reflected to the light source side into light that can contribute to the improvement of the front luminance. Then, by adjusting the selective reflection wavelength band of the reflective polarizer, the above effect can be exerted with less wavelength dependency in a wide wavelength region. Furthermore, since the polarizing element of the present invention has less dependency on the characteristics of the light source than the collimation and condensing system by combining the interference filter and the bright line light source of the prior art, it can be applied to any polarized light source and image display device. Can be used. For example, when used as a polarizer on the backlight side of a liquid crystal display element, it is possible to obtain a bright display with excellent visibility. Further, since the light utilization efficiency of the diffused light emitted from the light source is excellent, an image display device such as a high-brightness polarized light source device, an organic EL display device, a PDP, or a CRT can be formed.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing a mechanism of simultaneous expression of light collection and luminance improvement in an embodiment in which a reflective circular polarizer and a C plate are combined in a polarizing element of the present invention.
FIG. 2 is a diagram illustrating symbols representing natural light, circularly polarized light, and linearly polarized light in the present invention.
FIG. 3 is a schematic diagram of circular polarization using a combination of a linear polarizer and a quarter-wave plate.
FIG. 4 is a diagram showing a mechanism of simultaneous expression of light collection and luminance improvement in an embodiment in which a reflective linear polarizer, a C plate, and a quarter wavelength plate are combined in the polarizing element of the present invention.
5 is a schematic diagram showing angles formed by respective layers in the polarizing element of FIG. 4. FIG.
FIG. 6 is a diagram showing a mechanism of simultaneous expression of light collection and luminance improvement in an embodiment in which a reflective linear polarizer and a quarter wavelength plate satisfying Nz ≧ 2 are combined in the polarizing element of the present invention. .
7 is a schematic diagram showing angles formed by respective layers in the polarizing element of FIG. 6. FIG.
FIG. 8 is a diagram illustrating a mechanism of simultaneous expression of light collection and luminance improvement in an embodiment in which a reflective linear polarizer and a half-wave plate with Nz ≧ 1.5 are combined in the polarizing element of the present invention. It is.
9 is a schematic diagram showing angles formed by respective layers in the polarizing element of FIG. 8. FIG.
FIG. 10 is a schematic diagram showing an example of optical characteristics of a negative C plate.
FIG. 11 is a schematic view of a retardation layer including liquid crystal molecules that are homeotropically aligned.
FIG. 12 is a schematic diagram of a retardation layer including a discotic liquid crystal.
FIG. 13 is a schematic view of a retardation layer containing an inorganic layered compound.
FIG. 14 is a diagram showing an example of a bonding angle of each layer when a reflective linear polarizer, a C plate, and a quarter wavelength plate are combined in the polarizing element of the present invention.
15 is an explanatory diagram showing light conversion paths in the polarizing element of FIG. 14 by Poincare spheres.
FIG. 16 is a diagram showing the light condensing and luminance improving performance of the polarizing element of Example 1.
FIG. 17 is a diagram showing the light condensing and luminance enhancement performance of the polarizing elements of Examples 5 and 6.
[Explanation of symbols]
1 to 58 natural light, circularly polarized light or linearly polarized light
201, 203 Reflective circular polarizer
202 C plate
301 natural light
302 linear polarizer
303 Linearly polarized light
304 1/4 wave plate
305 circularly polarized light
404, 408 reflective linear polarizer
405, 407 quarter wave plate
406 C plate
609, 612 Reflective linear polarizer
610, 611 quarter wave plate
813, 815 Reflective linear polarizer
814 half wave plate
1101, 1201 Liquid crystal molecules
1301 Negative uniaxially oriented crystalline flakes
1401, 1405 Reflective linear polarizer
1402, 1404 1/4 wavelength plate
1403 C plate

Claims (17)

Including at least two reflective polarizers and a retardation layer disposed therebetween, wherein the two reflective polarizers selectively transmit one of clockwise circularly polarized light and counterclockwise circularly polarized light, and the other. The two-layer reflective circular polarizer is configured such that at least a part of the selective reflection wavelength bands in the selective reflection of polarized light overlap each other and pass through the two-layer reflective circular polarizer. Polarizing elements in which the rotational directions of the circularly polarized light are the same and the retardation layer satisfies the conditions of the following formulas (I) and (II).
R ≦ (λ / 10) (I)
R ′ ≧ (λ / 8) (II)
In formulas (I) and (II):
λ is the wavelength of light incident on the retardation layer,
R is an absolute value of a phase difference (in-plane phase difference) between the X-axis direction and the Y-axis direction with respect to incident light from the Z-axis direction (normal direction), and the X-axis direction is the retardation layer. Is the direction (in-plane slow axis direction) in which the refractive index is maximum, and the Y-axis direction is a direction (in-plane advance phase) perpendicular to the X-axis direction in the plane of the retardation layer. The Z-axis direction is the thickness direction of the retardation layer perpendicular to the X-axis direction and the Y-axis direction,
R ′ is an absolute value of the phase difference between the X′-axis direction and the Y′-axis direction with respect to incident light from a direction inclined by 30 ° or more with respect to the Z-axis direction, and the X′-axis direction is the Z-axis direction. It is an axial direction in the retardation layer plane perpendicular to the incident direction of incident light inclined by 30 ° or more with respect to the direction, and the Y′-axis direction is a direction perpendicular to the incident direction and the X′-axis direction. . The polarizing element according to claim 1, wherein regions of the selective reflection wavelength bands in the two-layer reflective circular polarizer that overlap each other include a wavelength range of 540 to 560 nm. It includes at least two reflective linear polarizers, a retardation layer disposed between them, and two quarter-wave plates, and one of the quarter-wave plates includes the reflective linear polarizer. The other quarter-wave plate is disposed between the other reflection linear polarizer and the retardation layer, and the two reflection lines are disposed between the other retardation linear polarizer and the retardation layer. In the polarizer, at least a part of the selective reflection wavelength bands in the selective reflection of polarized light overlap each other, and the quarter wavelength plate located on one surface side of the retardation layer has an in-plane slow axis on the same side. The quarter-wave plate that forms an angle of 40 ° to 50 ° with the polarization axis of the reflective linear polarizer located on the other side of the retardation layer and has the in-plane slow axis on the same side An angle of −40 ° to −50 ° with the polarization axis of the reflective linear polarizer located at the center, and an in-plane retardation of the two-layer quarter-wave plate Angle formed between is arbitrary, the retardation layer satisfies the following formula (I) and satisfies the condition polarizing element (III).
R ≦ (λ / 10) (I)
R ′ ≧ (λ / 4) (III)
In formulas (I) and (III):
λ is the wavelength of light incident on the retardation layer,
R is an absolute value of a phase difference (in-plane phase difference) between the X-axis direction and the Y-axis direction with respect to incident light from the Z-axis direction (normal direction), and the X-axis direction is the retardation layer. Is the direction (in-plane slow axis direction) in which the refractive index is maximum, and the Y-axis direction is a direction (in-plane advance phase) perpendicular to the X-axis direction in the plane of the retardation layer. The Z-axis direction is the thickness direction of the retardation layer perpendicular to the X-axis direction and the Y-axis direction,
R ′ is an absolute value of the phase difference between the X′-axis direction and the Y′-axis direction with respect to incident light from a direction inclined by 30 ° or more with respect to the Z-axis direction, and the X′-axis direction is the Z-axis direction. It is an axial direction in the retardation layer plane perpendicular to the incident direction of incident light inclined by 30 ° or more with respect to the direction, and the Y′-axis direction is a direction perpendicular to the incident direction and the X′-axis direction. . At least one of two selective reflection wavelength bands in the selective reflection of polarized light. The reflective linear polarizer includes at least two reflective linear polarizers and two quarter-wave plates disposed between them. And the in-plane slow axis of the quarter-wave plate forms an angle of 40 ° to 50 ° with the polarization axis of the reflective linear polarizer located on the same side, and the other 1/4 The in-plane slow axis of the wave plate forms an angle of −40 ° to −50 ° with the polarization axis of the reflective linear polarizer located on the same side, and the in-plane slow axis of the two-layer quarter-wave plate The angle between each other is arbitrary, and each of the quarter wavelength plates satisfies the following formula (IV).
Nz ≧ 2.0 (IV)
However, Nz = (nx−nz) / (nx−ny)
In formula (IV):
nx, ny, and nz are refractive indexes in the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively, in the quarter-wave plate, and the X-axis direction is refracted in the plane of the quarter-wave plate. The direction in which the rate is maximum (in-plane slow axis direction), and the Y-axis direction is a direction perpendicular to the X-axis direction (in-plane fast axis direction) in the plane of the quarter-wave plate. The Z-axis direction is the thickness direction of the quarter-wave plate perpendicular to the X-axis direction and the Y-axis direction. Including at least a two-layer reflective linear polarizer and a half-wave plate disposed therebetween, wherein the two-layer reflective linear polarizer has at least a part of a selective reflection wavelength band in selective reflection of polarized light. The in-plane slow axis of the half-wave plate forms an angle of 40 ° to 50 ° with the polarization axis of one reflective linear polarizer, and −40 with the polarization axis of the other reflective linear polarizer A polarizing element having an angle of -50 ° and the half-wave plate satisfying the following formula (V).
Nz ≧ 1.5 (V)
However, Nz = (nx−nz) / (nx−ny)
In formula (V):
nx, ny, and nz are refractive indexes in the X-axis direction, the Y-axis direction, and the Z-axis direction of the half-wave plate, respectively, and the X-axis direction is refracted in the plane of the half-wave plate. The direction in which the rate is maximum (in-plane slow axis direction), and the Y-axis direction is a direction perpendicular to the X-axis direction (in-plane fast axis direction) in the plane of the half-wave plate The Z-axis direction is the thickness direction of the half-wave plate perpendicular to the X-axis direction and the Y-axis direction. The polarizing element according to any one of claims 3 to 5 , wherein regions where selective reflection wavelength bands of the two-layer reflective linear polarizers overlap each other include a wavelength range of 540 to 560 nm. The retardation layer comprises a cholesteric liquid crystal compound fixed in a planar alignment state of claims 1 to 3, the selective reflection wavelength band of the retardation layer is present in a wavelength region other than the visible light region (380 nm to 780 nm) The polarizing element in any one. The retardation layer, the polarizing element according to claim 1 comprising a rod-like liquid crystal compound fixed in homeotropic alignment state. The retardation layer, the polarizing element according to claim 1 comprising a discotic liquid crystal compound fixed in nematic phase or columnar phase alignment state. The retardation layer, the polarizing element according to claim 1 comprising a non-liquid crystal polymer biaxially oriented. The retardation layer includes an inorganic layered compound having negative uniaxiality, and the alignment state of the inorganic layered compound is such that the optical axis direction of the retardation layer is a direction perpendicular to the surface (normal direction). The polarizing element according to claim 1 , wherein the polarizing element is fixed to the surface. It further includes another layer having a quarter-wave plate function at least in the front direction, and this layer is disposed further outside the reflective circular polarizer located on the viewer side of the two layers of reflective circular polarizers. The polarizing element according to claim 1 or 2 . Further comprising an absorbent dichroic polarizing plate, the absorption dichroic polarizing plate, according to claim 12, which is located further outside of the another layer having at least a quarter-wave plate function in the front direction Polarizing element. Wherein each component, the polarization element according to any one of claims 1 to 13 are laminated through a layer of transparent adhesive or pressure-sensitive adhesive. Light source, a reflective layer, and a polarizing element according to any of claims 1-14, polarized light source that the polarizing element is laminated on the light source via the reflecting layer. A liquid crystal display device comprising the polarized light source according to claim 15 , wherein a liquid crystal cell is further laminated on the polarizing element. An image display device comprising a polarizing element according to any of claims 1-14.

Images