JP2004302075A - Method for manufacturing wideband cholesteric liquid crystal film, circularly polarizing plate, linearly polarizing element, lighting device and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of manufacturing a wideband cholesteric liquid crystal film having a wideband reflection band even in a long wavelength region. <P>SOLUTION: In the method for manufacturing a wideband cholesteric liquid crystal film having a reflection bandwidth of ≥200 nm, a liquid crystal mixture containing a polymerizable mesogen compound (A) and a polymerizable chiral agent (B) is applied on an oriented substrate and polymerized and cured under UV irradiation. At this time, in a state where the liquid crystal mixture is in contact with oxygen-containing gas, UV irradiation is carried out ≥3 times from the substrate side at a temperature of ≥20°C with a UV irradiation intensity of 1-200 mW/cm<SP>2</SP>within 0.2-30 seconds while reducing UV irradiation intensity and prolonging UV irradiation time every time a UV irradiation step is finished, and then UV irradiation is carried out in the absence of oxygen. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

（但し、Ｒ_１ は水素原子またはメチル基を示す。ｎは１〜５の整数を表す。）で表される化合物であることを特徴とする上記１〜４のいずれかに記載の広帯域コレステリック液晶フィルムの製造方法。
【００３０】
６．上記１〜５のいずれかに記載の製造方法により得られた広帯域コレステリック液晶フィルムを用いた円偏光板。
【００３１】
７．偏光の選択反射の波長帯域が互いに重なっている少なくとも２層の反射偏光子（ａ）の間に、
正面位相差（法線方向）がほぼゼロで、法線方向に対し３０°以上傾けて入射した入射光に対してλ／８以上の位相差を有する位相差層（ｂ）が配置されている偏光素子であって、
反射偏光子（ａ）が、上記６記載の円偏光板であることを特徴とする偏光素子。
【００３２】
８．少なくとも２層の反射偏光子（ａ）の選択反射波長が、５５０ｎｍ±１０ｎｍの波長範囲で互いに重なっていることを特徴とする上記７記載の偏光素子。
【００３３】
９．位相差層（ｂ）が、選択反射波長域を可視光領域以外に有するコレステリック液晶相のプラナー配向を固定したもの、
棒状液晶のホメオトロピック配向状態を固定したもの、
ディスコチック液晶のネマチック相またはカラムナー相配向状態を固定したもの、
ポリマーフィルムを２軸配向したもの、または、
負の１軸性を有する無機層状化合物を面の法線方向に光軸がなるように配向固定したものであることを特徴とする上記７または８記載の偏光素子。
【００３４】
１０．上記６記載の円偏光板、または上記７〜９のいずれかに記載の偏光素子に、λ／４板が積層されており、透過で直線偏光が得られることを特徴とする直線偏光素子。
【００３５】
１１．円偏光板であるコレステリック液晶フィルムを、λ／４板に対し、ピッチ長が連続的に狭くなるように積層して得られる上記１０記載の直線偏光素子。
【００３６】
１２．λ／４板が、２軸延伸して斜め入射光線の位相差補正を行い、視野角改善した位相差板であることを特徴とする上記１０または１１記載の直線偏光素子。
【００３７】
１３．λ／４板が、ネマチック液晶またはスメクチック液晶を塗布、固定化して得られる液晶ポリマー型位相差板であることを特徴とする上記１０または１１記載の直線偏光素子。
【００３８】
１４．λ／４板が、面内の主屈折率をｎｘ、ｎｙ、厚さ方向の主屈折率をｎｚとしたとき、式：（ｎｘ−ｎｚ）／（ｎｘ−ｎｙ）で定義されるＮｚ係数が−０．５〜−２．５を満足するものであることを特徴とする上記１０〜１３のいずれかに記載の直線偏光素子。
【００３９】
１５．上記１０〜１４のいずれかに記載の直線偏光素子のλ／４板に、さらにλ／２板が積層されていることを特徴とする直線偏光素子。
【００４０】
１６．上記１０〜１５のいずれかに記載の直線偏光素子の透過軸と、透過軸方向を合わせた吸収型偏光子を、直線偏光素子のλ／４板側に積層したことを特徴とする直線偏光素子。
【００４１】
１７．裏面側に反射層を有する面光源の表面側に上記６記載の円偏光板、上記７〜９のいずれかに記載の偏光素子、または上記１０〜１６のいずれかに記載の直線偏光素子を有することを特徴とする照明装置。
【００４２】
１８．上記１７記載の照明装置の光出射側に、液晶セルを有することを特徴とする液晶表示装置。
【００４３】
１９．液晶セルに対して、視認側に、液晶セルを透過した視認側の光線を拡散する視野角拡大フィルムを配置してなることを特徴とする上記１８記載の視野角拡大液晶表示装置。
【００４４】
２０．視野角拡大フィルムとして、実質的に後方散乱、偏光解消を有さない拡散板を用いたことを特徴とする上記１９記載の視野角拡大液晶表示装置。
【００４５】
（作用）
上記のように、本発明では、反射帯域を広帯域化させるために、液晶混合物が酸素を含む気体と接触している状態で配向基材側から紫外線照射する工程（１）における紫外線照射を複数回のパルス照射により行い、各パルス照射における、紫外線照射の照度・照射温度としてそれぞれ異なる条件を用いている。これにより、重合性の液晶混合物の反応挙動のより緻密な制御を実現でき、従来に比して、高効率の生産速度により、広帯域コレステリック液晶フィルムが得られる。
【００４６】
すなわち、工程（１）の紫外線照射条件は回数が増える毎に、紫外線照射強度を低く、かつ紫外線照射時間を長くしている。照射強度の違いにより単位時間あたりの液晶組成物中において光反応開始剤の紫外線反応によって発生するラジカル量を１回目の紫外線照射と２回目の紫外線照射時では大きく変えている。１回目の紫外線照射では、反応初期のモノマーリッチな条件で瞬間的に大量のラジカルを形成し、酸素阻害と液晶組成物の吸収によりラジカル存在分布に厚み方向の大きな傾斜を形成せしめる。これにより平均分子量１００００〜５０００００程度のポリマー／オリゴマーが形成され、しかも厚み方向に濃度分布が形成される。また、この際に、液晶配合物中の重合性メソゲン化合物（Ａ）と重合性カイラル剤（Ｂ）の反応速度が異なるために重合比が厚み方向で異なる。このため重合性カイラル剤（Ｂ）がリッチな面はコレステリックピッチが短く、逆方向面は長くなる。これにより全体として広帯域な反射波長を有するコレステリック液晶フィルムが得られる。
【００４７】
このようにして得られた広帯域コレステリック液晶フィルムは広帯域円偏光反射板として機能し、特許文献１乃至４等と光学特性的には同等の性質を有するとともに、従来の製造方法に比べて、積層枚数の低減により厚みを低減でき、さらには簡単に短時間で製造でき、生産速度の向上により、低コスト化が可能である。
【００４８】
上記本発明の製造方法で得られた広帯域コレステリック液晶フィルムは、その選択反射波長の反射帯域巾が２００ｎｍ以上と広く、広帯域の反射帯域巾を有する。反射帯域巾は、３００ｎｍ以上、さらには４００ｎｍ以上、さらには４５０ｎｍであるのが好ましい。また２００ｎｍ以上の反射帯域巾は可視光領域、特に４００〜９００ｎｍの波長領域において有することが好ましい。
【００４９】
円偏光反射板が長波長域にも広帯域の反射帯域を有することは、液晶表示装置の良好な視野角特性を得るために重要な問題である。実用的な視野角範囲で透過光線に着色が見られないためには選択反射の長波長端が８００〜９００ｎｍに達する必要がある。本発明の製造方法によれば、かかる長波長域にも反射帯域を有する広帯域コレステリック液晶フィルムを得ることができる。かかる広帯域コレステリック液晶フィルムは、単に高輝度を得るための反射偏光子として用いる場合だけでなく、位相差板などの他の光学素子と組み合わせて作成する偏光素子の場合でも同様に正面以外の斜め入射光線に対する安定した光学特性が求められる。
【００５０】
【発明の実施の形態】
本発明の広帯域コレステリック液晶フィルムは、重合性メソゲン化合物（Ａ）および重合性カイラル剤（Ｂ）を含む液晶混合物を紫外線重合して得られる。
【００５１】
重合性メソゲン化合物（Ａ）は、重合性官能基を少なくとも１つ有し、これに環状単位等からなるメソゲン基を有するものが好適に用いられる。重合性官能基としては、アクリロイル基、メタクリロイル基、エポキシ基、ビニルエーテル基等があげられるが、これらのなかでもアクリロイル基、メタクリロイル基が好適である。また重合性官能基を２つ以上有するものを用いることにより架橋構造を導入して耐久性を向上させることもできる。メソゲン基となる前記環状単位としては、たとえば、ビフェニル系、フェニルベンゾエート系、フェニルシクロヘキサン系、アゾキシベンゼン系、アゾメチン系、アゾベンゼン系、フェニルピリミジン系、ジフェニルアセチレン系、ジフェニルベンゾエート系、ビシクロへキサン系、シクロヘキシルベンゼン系、ターフェニル系等があげられる。なお、これら環状単位の末端は、たとえば、シアノ基、アルキル基、アルコキシ基、ハロゲン基等の置換基を有していてもよい。前記メソゲン基は屈曲性を付与するスペーサ部を介して結合していてもよい。スペーサ部としては、ポリメチレン鎖、ポリオキシメチレン鎖等があげられる。スペーサ部を形成する構造単位の繰り返し数は、メソゲン部の化学構造により適宜に決定されるがポリメチレン鎖の繰り返し単位は０〜２０、好ましくは２〜１２、ポリオキシメチレン鎖の繰り返し単位は０〜１０、好ましくは１〜３である。
【００５２】
重合性メソゲン化合物（Ａ）のモル吸光係数は、５０〜５００ｄｍ^３ ｍｏｌ^−１ｃｍ^−１＠３６５ｎｍであることが好ましい。前記モル吸光係数を有するものは紫外線吸収能を有する。モル吸光係数は、１００〜２５０ｄｍ^３ ｍｏｌ^−１ｃｍ^−１＠３６５ｎｍがより好適である。モル吸光係数が５０ｄｍ^３ ｍｏｌ^−１ｃｍ^−１＠３６５ｎｍより小さいと十分な重合速度差がつかずに広帯域化し難い。一方、５００ｄｍ^３ ｍｏｌ^−１ｃｍ^−１＠３６５ｎｍより大きいと重合が完全に進行せずに硬化が終了しない場合がある。なお、モル吸光係数は、各材料の分光光度スペクトルを測定し、得られた３６５ｎｍの吸光度から測定した値である。
【００５３】
重合性官能基を１つ有する重合性メソゲン化合物（Ａ）は、たとえば、下記化１の一般式：
【化３】

（但し、Ｒ_１ は水素原子またはメチル基を示す。ｎは１〜５の整数を表す。）で表される化合物があげられる。
【００５４】
重合性官能基を１つ有する重合性メソゲン化合物（Ａ）の具体例としては、たとえば、下記化４、
【化４】

で表される化合物があげられる。
【００５５】
また、重合性カイラル剤（Ｂ）としては、たとえば、ＢＡＳＦ社製ＬＣ７５６があげられる。
【００５６】
上記重合性カイラル剤（Ｂ）の配合量は、重合性メソゲン化合物（Ａ）と重合性カイラル剤（Ｂ）の合計１００重量部に対して、１〜２０重量部程度が好ましく、３〜７重量部がより好適である。重合性メソゲン化合物（Ａ）と重合性カイラル剤（Ｂ）の割合により螺旋ねじり力（ＨＴＰ）が制御される。前記割合を前記範囲内とすることで、得られるコレステリック液晶フィルムの反射スペクトルが長波長域をカバーできるように反射帯域を選択することができる。
【００５７】
また液晶混合物には、通常、光重合開始剤（Ｃ）を含む。光重合開始剤（Ｃ）としては各種のものを特に制限なく使用できる。例えば、チバスペシャルティケミカルズ社製のイルガキュア１８４、イルガキュア９０７、イルガキュア３６９、イルガキュア６５１等があげられる。光重合開始剤の配合量は、重合性メソゲン化合物（Ａ）と重合性カイラル剤（Ｂ）の合計１００重量部に対して、０．０１〜１０重量部程度が好ましく、０．０５〜５重量部がより好適である。
【００５８】
前記混合物には、得られるコレステリック液晶フィルムの帯域幅を広げるために、紫外線吸収剤を混入して厚み方向での紫外線露光強度差を大きくするすることができる。また、モル吸光係数の大きな光反応開始剤を用いることで同様の効果を得ることもできる。
【００５９】
前記混合物は溶液として用いることができる。溶液を調製する際に用いられる溶媒としては、通常、クロロホルム、ジクロロメタン、ジクロロエタン、テトラクロロエタン、トリクロロエチレン、テトラクロロエチレン、クロロベンゼンなどのハロゲン化炭化水素類、フェノール、パラクロロフェノールなどのフェノール類、ベンゼン、トルエン、キシレン、メトキシベンゼン、１，２−ジメトキベンゼンなどの芳香族炭化水素類、その他、アセトン、メチルエチルケトン、酢酸エチル、ｔｅｒｔ−ブチルアルコール、グリセリン、エチレングリコール、トリエチレングリコール、エチレンブリコールモノメチルエーテル、ジエチレングリコールジメチルエーテル、エチルセルソルブ、ブチルセルソルブ、２−ピロリドン、Ｎ−メチル−２−ピロリドン、ピリジン、トリエチルアミン、テトラヒドロフラン、ジメチルホルムアミド、ジメチルアセトアミド、ジメチルスルホキシド、アセトニトリル、ブチロニトリル、二硫化炭素、シクロペンタノン、シクロヘキサノンなどを用いることができる。使用する溶媒としては、特に制限されないが、メチルエチルケトン、シクロヘキサノン、シクロペンタノン等が好ましい。溶液の濃度は、サーモトロピック液晶性化合物の溶解性や最終的に目的とするコレステリック液晶フィルムの膜厚に依存するため一概には言えないが、通常３〜５０重量％程度とするのが好ましい。
【００６０】
本発明の広帯域コレステリック液晶フィルムの製造は、前記液晶混合物を配向基材に塗布する工程、および前記液晶混合物に紫外線照射を行い重合硬化する工程を含む。
【００６１】
配向基材としては、従来知られているものを採用できる。たとえば、基板上にポリイミドやポリビニルアルコール等からなる薄膜を形成して、それをレーヨン布等でラビング処理したラビング膜、斜方蒸着膜、シンナメートやアゾベンゼンなど光架橋基を有するポリマーあるいはポリイミドに偏光紫外線を照射した光配向膜、延伸フィルムなどが用いられる。その他、磁場、電場配向、ずり応力操作により配向させることもできる。
【００６２】
基材の種類は特に限定しないが、基材側から照射線（紫外線）を照射する手法上、透過率の高い素材が望ましい。たとえば、基材は、２００ｎｍ以上４００ｎｍ以下、より望ましくは３００ｎｍ以上４００ｎｍ以下の紫外域に対して透過率１０％以上、望ましくは２０％以上であることが求められる。具体的には、波長３６５ｎｍの紫外光に対する透過率が１０％以上、さらには２０％以上のプラスチックフィルムであることが好ましい。なお、透過率は、ＨＩＴＡＣＨＩ製Ｕ−４１００Ｓｐｅｃｔｒｏｐｈｏｔｏｍｅｔｅｒにより測定される値である。
【００６３】
なお、前記基板としては、ポリエチレンテレフタレート、トリアセチルセルロース、ノルボルネン樹脂、ポリビニルアルコール、ポリイミド、ポリアリレート、ポリカーボネート、ポリスルホンやポリエーテルスルホン等のプラスチックからなるフィルムやガラス板が用いられる。例えば富土写真フイルム社製トリアセチルセルロースやＪＳＲ製ＡＲＴＯＮ、日本ゼオン製ゼオネックスなどがあげられる。
【００６４】
また、特開２００１−３４３５２９号公報（ＷＯ０１／３７００７）に記載のポリマーフィルム、たとえば、（Ａ）側鎖に置換および／または非置換イミド基を有する熱可塑性樹脂と、（Ｂ）側鎖に置換および／非置換フェニルならびにニトリル基を有する熱可塑性樹脂を含有する樹脂組成物があげられる。具体例としてはイソブチレンとＮ−メチルマレイミドからなる交互共重合体とアクリロニトリル・スチレン共重合体とを含有する樹脂組成物のフィルムがあげられる。フィルムは樹脂組成物の混合押出品などからなるフィルムを用いることができる。
【００６５】
前記基材はコレステリック液晶層と貼り合わせたまま用いても良いし剥離除去しても良い。貼り合わせたまま用いる場合には位相差値が実用上十分小さな材質を用いる。
【００６６】
基材を貼り合わせたまま用いる場合には、基材は紫外線が照射されても分解・劣化・黄変しないものが望ましい。たとえば、前述の基材には光安定剤等を配合することのより所用の目的を達成しうる。光安定剤としては、チバスペシャルティケミカルズ社製チヌビン１２０、同１４４等が好適に用いられる。露光光線から波長３００ｎｍ以下をカットしておけば着色・劣化・黄変を低減することができる。
【００６７】
前記液晶混合物の塗布厚み（溶液の場合は溶媒乾燥後の塗布厚み）は１〜２０μｍ程度が好ましい。塗布厚みが１μｍより薄い場合は、反射帯域巾は確保できるものの偏光度そのものが低下する傾向があり好ましくない。塗布厚みは２μｍ以上、さらには３μｍ以上であるのが好ましい。一方、塗布厚みは２０μｍより厚い場合には反射帯域巾・偏光度共に顕著な向上は見られず、単に高コストとなり好ましくない。塗布厚みは１５μｍ以下、さらには１０μｍ以下がより好適である。
【００６８】
配向基材に前記混合溶液を塗工する方法としては、例えば、ロールコート法、グラビアコート法、スピンコート法、バーコート法などを採用することができる。混合溶液の塗工後、溶媒を除去し、基板上に液晶層を形成させる。溶媒の除去条件は、特に限定されず、溶媒をおおむね除去でき、液晶層が流動したり、流れ落ちたりさえしなければ良い。通常、室温での乾燥、乾燥炉での乾燥、ホットプレート上での加熱などを利用して溶媒を除去する。
【００６９】
次いで、前記配向基材上に形成された液晶層を液晶状態とし、コレステリック配向させる。たとえば、液晶層が液晶温度範囲になるように熱処理を行う。熱処理方法としては、上記の乾燥方法と同様の方法で行うことができる。熱処理温度は、液晶材料や配向基材の種類により異なるため一概には言えないが、通常６０〜３００℃、好ましくは７０〜２００℃の範囲において行う。また熱処理時間は、熱処理温度および使用する液晶材料や配向基材の種類によって異なるため一概には言えないが、通常１０秒間〜２時間、好ましくは２０秒間〜３０分間の範囲で選択される。
【００７０】
配向基材に塗布して液晶混合物を紫外線照射する工程は上記工程（１）、（２）を含む。
【００７１】
工程（１）では、液晶混合物が酸素を含む気体と接触している状態で、２０℃以上の温度下に、１〜２００ｍＷ／ｃｍ^２ の紫外線照射強度、０．２〜３０秒間の範囲内の紫外線照射を、回数が増える毎に、紫外線照射強度を低く、かつ紫外線照射時間を長くしながら、３回以上、配向基材側から紫外線照射する。
【００７２】
これにより、液晶混合物を重合して、平均分子量１００００〜５０００００程度のポリマー／オリゴマーを形成するとともに、配向基材側とその反対側（酸素界面側）の厚み方向に、酸素阻害による反応速度差と、液晶組成物の紫外線吸収によるラジカル発生量の差異が生じ、厚み方向に、ポリマー／オリゴマーの生成量が連続分布した層を形成させる。これと同時に、未重合モノマー成分の濃度傾斜勾配を均一化させることで、ピッチを連続的に変化させる。
【００７３】
上記の通り工程（１）では、広帯域化させるため紫外線照射におけるパルス照射において、露光の照度・照射時間はそれぞれ異なる条件を用いる。これは、露光の照度によって空気界面側から浸透する酸素による重合阻害の有効深さが異なることを利用している。
【００７４】
工程（１）における、紫外線照射時の温度は、液晶混合物を良好な配向状態で重合硬化させるため、２０℃以上の温度で行う。一方、温度の上限は特に制限されないが、１２０℃以下とするのが好適である。温度が１２０℃より高いと、照射中に拡散が起こってしまい管理が難しくなる場合がある。これらの点から前記温度は２０℃〜８０℃が好適である。
【００７５】
紫外線照射強度は、１〜２００ｍＷ／ｃｍ^２ であり、４〜１００ｍＷ／ｃｍ^２ が好ましい。紫外線照射強度が１ｍＷ／ｃｍ^２ より低いと、厚み方向にモノマー分布が形成されるほどの重合がなされないために広帯域化しなくなる。また紫外線照射強度が２００ｍＷ／ｃｍ^２ より高いと重合反応速度が拡散速度より大きくなるために、広帯域化しなくなるため好ましくない。
【００７６】
工程（１）におけるパルス照射の１回の紫外線照射時間は０．２〜３０秒間の範囲内で調整される。紫外線照射時間は照度による。パルス照射の回数が増える毎に、紫外線照射強度を低く、かつ紫外線照射時間を長くしながら行う。パルス照射の回数は３回以上、好ましくは３〜６回、さらに好ましくは４〜５回である。
【００７７】
具体的には紫外線照度が３０〜２００ｍＷ／ｃｍ^２ 、好ましくは３０〜１００ｍＷ／ｃｍ^２ の範囲では紫外線照射時間は０．２〜５秒間が好ましく、より好ましくは０．５秒間〜２秒間である。０．２秒間より短いと、厚み方向にモノマー分布がつくほどの重合がなされないために広帯域化しなくなる傾向がある。また５秒間より長いと、コレステリック層のピッチ変化が基材側から空気界面側へと大から小になる連続変化ではなく、不連続変化となるため好ましくない。不連続ピッチ変化だと、斜めから見た時の着色がひどくなる。紫外線照度が１５〜３０ｍＷ／ｃｍ^２ の範囲では、紫外線照射時間は３〜２０秒間が好ましく、より好ましくは５秒間〜１５秒間である。３秒間より短いと、厚み方向にモノマー分布がつくほどの重合がなされないために広帯域化しなくなる傾向がある。また１５秒間より長いと、重合時間が長くなりプロセス上不利になるため好ましくない。紫外線照度が１〜１５ｍＷ／ｃｍ^２ の範囲では、紫外線照射時間は１０〜３０秒間が好ましく、より好ましくは１０〜２０秒間である。１０秒間より短いと、厚み方向にモノマー分布がつくほどの重合がなされないために広帯域化しなくなる傾向がある。また３０秒間より長いと．重合時間が長くなりプロセス上不利になるため好ましくない。
【００７８】
紫外線照射における露光環境は、配向基材に塗布された液晶混合物が、酸素を含む気体と接触している状態で行う。酸素を含む気体が０．５％以上の酸素を含んでいることが好ましい。かかる環境は、酸素重合阻害を利用できるものであればよく、一般的な大気雰囲気下で行うことができる。また、厚み方向のピッチ制御を目的とする波長巾、重合に必要な速度を鑑み、酸素濃度を増減させてもよい。なお、大気雰囲気下では光重合開始剤（Ｃ）の必要量が増大する傾向にあるがイルガキュア１８４、イルガキュア９０７（いずれもチバスペシャルティケミカルズ社製）を用いれば、重合性メソゲン化合物（Ａ）と重合性カイラル剤（Ｂ）の合計１００重量部に対して、１〜５重量部程度の添加量で所用の目的を達成できる。
【００７９】
なお、上記紫外線照射にあたっては、形成されるポリマー／オリゴマーの重量平均分子量が小さすぎると拡散速度が高くなりすぎる。したがって、制御不能な拡散速度によって、ポリマー／オリゴマーの濃度勾配が均一化してしまわないように注意するのがよい。コレステリックピッチ長の液晶層厚み方向での大きな変化を形成するだけでなく、これを維持する必要がある。前記ポリマー／オリゴマーが余りにも低分子量では形成した傾斜が維持できず、分子拡散によって構造が消失してしまう。拡散速度を工業条件的に管理するための条件を満たすには、重量平均分子量１００００〜５０００００程度の範囲にポリマー／オリゴマーが形成される。ポリマー／オリゴマーの重量平均分子量は１０００００〜３０００００であるのが好ましい。なお、ポリマー／オリゴマーの重量平均分子量は、ＧＰＣ法により測定される値である。なお、重量平均分子量は、ポリエチレンオキサイドを標準試料に用い算出した。本体：東ソー製のＨＬＣ−８１２０ＧＰＣ、カラム：東ソー製のＳｕｐｅｒＡＷＭ−Ｈ＋ＳｕｐｅｒＡＷＭ−Ｈ＋ＳｕｐｅｒＡＷ３０００（各６ｍｍφ×１５ｃｍ，計４５ｃｍ）、カラム温度：４０℃、溶離液：１０ｍＭ−ＬｉＢｒ／ＮＭＰ、流速：０．４ｍｌ／ｍｉｎ、入口圧：８．５ＭＰａ、サンプル濃度：０．１％ＮＭＰ溶液、検出器：示差屈折計（ＲＩ）、である。
【００８０】
かかる工程（１）では、パルス照射の回数が増える毎に、酸素界面側から浸透する酸素による重合阻害の有効深さをより深くすることができ、ポリマー／オリゴマーを厚み方向に濃度傾斜して形成させたために逆に形成される未重合モノマー成分の濃度傾斜勾配を均一化させることができる。それと同時に、配向基板側の長ピッチ領域のみ反応を進行させることにより、配向基板側の長ピッチ化をさらに増大させることができる。
【００８１】
特許文献２では，第１紫外線照射と第２紫外線照射との温度条件を変え、かつ組成比が厚み方向で変化するに必要な時間を暗所にて別途設けている。しかし、この方法で実質可視光線全域をカバーしようとすると、この温度変化による物質移動の待ち時間は１２０分間程度は必要である。一方、本発明の製造方法では、特に暗所は必要でない。さらには１分間以内の短い時間で工程を終了することが可能なため、実用的な高効率生産速度を生み出すことが可能である。
【００８２】
前述のように工程（１）による広帯域化により後述の実施例に示す広帯域化が可能であり、斜め入射光線のブルーシフトによる着色・色抜けが生じる視野角度が極めて大きくなり、視角による着色は著しく低減せしめることができる。
【００８３】
次いで、工程（２）では、酸素不存在下で、紫外線照射する。かかる紫外線照射により、工程（１）で拡張されたコレステリック反射帯域を劣化させることなく、硬化させる。これにより、ピッチ変化構造を劣化させることなく固定する。
酸素不存在下は、たとえば不活性ガス雰囲気下とすることができる。不活性ガスは、前記液晶混合物の紫外線重合に影響を及ぼさないものであれば特に制限されない。かかる不活性ガスとしては、窒素、アルゴン、ヘリウム、ネオン、キセノン、クリプトン等があげらる。これらのなかでも、窒素が最も汎用性が高く好ましい。また、コレステリック液晶層に、透明基材を貼り合わせることにより、酸素不存在下とすることもできる。
【００８４】
工程（２）において、紫外線照射は、配向基材側、塗布した液晶混合物の側のいずれの側から行ってもよい。
【００８５】
紫外線照射条件は、液晶混合物が硬化する条件であれば特に制限されない。通常は、４０〜３００ｍＷ／ｃｍ^２ 程度の照射強度で、１〜６０秒間程度照射するのが好ましい。照射温度は、２０〜１００℃程度である。
【００８６】
これにより液晶層の架橋密度の向上・分子量増大により信頼性が著しく向上する。本発明では、工程（１）の第１紫外線照射、工程（２）の第２紫外線照射で酸素阻害を積極的に活用するため配向基材面側からの紫外線照射を行っている。このため反応率に厚み方向に大きな勾配を形成することが可能としているが、問題として空気界面側の重合率の低さから膜表面の硬度・強度の不足、または長期の信頼性の不足などの問題が生じるおそれがある。このため、工程（２）では、酸素不存在雰囲気下にて第３紫外線照射を行い、残存モノマーを重合完結させ、膜質の強化を行っている。この場合、空気雰囲気下（酸素存在下）では表面の反応率は十分に向上せず、反応率が９０％を上回ることは困難である。したがって、十分な信頼性を得るには、酸素不存在下にて紫外線照射を行うことが望まれる。照射面方向は特に限定される物ではない。液晶層側からの照射が望ましいが、窒素雰囲気下では基材側からの照射でも十分に表面の反応は進行するからである。
【００８７】
こうして得られるコレステリック液晶フィルムは、基材から剥離することなく用いられる他、基材から剥離して用いてもよい。
【００８８】
本発明の広帯域コレステリック液晶フィルムは円偏光板として用いられる。円偏光板には、λ／４板を積層して直線偏光素子とすることができる。円偏光板であるコレステリック液晶フィルムは、λ／４板に対し、ピッチ長が連続的に狭くなるように積層するのが好ましい。
【００８９】
λ／４板としては、特に限定されないがポリカーボネート、ポリエチレンテレフタレート、ポリスチレン、ポリスルホン、ポリビニルアルコール、ポリメチルメタクリレート等のような延伸することで位相差を発生する汎用透明樹脂フィルムやＪＳＲ製ＡＲＴＯＮフィルムのようなノルボルネン系樹脂フィルム等が好適に用いられる。さらに２軸延伸を行い、入射角による位相差値変化を補償する位相差板を用いれば視野角特性を改善できるので好適である。また樹脂の延伸による位相差発現以外の例えば液晶を配向せしめることで得られるλ／４層を固定することで得られるλ／４板を用いても良い。この場合、λ／４板の厚みを大幅に低減できる。λ／４波長板の厚さは、通常０．５〜２００μｍであることが好ましく、特に１〜１００μｍであることが好ましい。
【００９０】
可視光域等の広い波長範囲でλ／４波長板として機能する位相差板は、例えば波長５５０ｎｍの淡色光に対してλ／４波長板として機能する位相差層と他の位相差特性を示す位相差層、例えばλ／２波長板として機能する位相差層とを重畳する方式などにより得ることができる。従って、偏光板と輝度向上フィルムの間に配置する位相差板は、１層又は２層以上の位相差層からなるものであってよい。
【００９１】
前記直線偏光素子の透過軸に、吸収型偏光子をその透過軸方向を合わせて貼り合わせて用いられる。
【００９２】
偏光子は、特に制限されず、各種のものを使用できる。偏光子としては、たとえば、ポリビニルアルコール系フィルム、部分ホルマール化ポリビニルアルコール系フィルム、エチレン・酢酸ビニル共重合体系部分ケン化フィルム等の親水性高分子フィルムに、ヨウ素や二色性染料等の二色性物質を吸着させて一軸延伸したもの、ポリビニルアルコールの脱水処理物やポリ塩化ビニルの脱塩酸処理物等ポリエン系配向フィルム等があげられる。これらのなかでもポリビニルアルコール系フィルムとヨウ素などの二色性物質からなる偏光子が好適である。これら偏光子の厚さは特に制限されないが、一般的に、５〜８０μｍ程度である。
【００９３】
ポリビニルアルコール系フィルムをヨウ素で染色し一軸延伸した偏光子は、たとえば、ポリビニルアルコールをヨウ素の水溶液に浸漬することによって染色し、元長の３〜７倍に延伸することで作製することができる。必要に応じてホウ酸やヨウ化カリウムなどの水溶液に浸漬することもできる。さらに必要に応じて染色の前にポリビニルアルコール系フィルムを水に浸漬して水洗してもよい。ポリビニルアルコール系フィルムを水洗することでポリビニルアルコール系フィルム表面の汚れやブロッキング防止剤を洗浄することができるほかに、ポリビニルアルコール系フィルムを膨潤させることで染色のムラなどの不均一を防止する効果もある。延伸はヨウ素で染色した後に行っても良いし、染色しながら延伸してもよし、また延伸してからヨウ素で染色してもよい。ホウ酸やヨウ化カリウムなどの水溶液中や水浴中でも延伸することができる。
【００９４】
前記偏光子は、通常、片側または両側に透明保護フィルムが設けられ偏光板として用いられる。透明保護フィルムは透明性、機械的強度、熱安定性、水分遮蔽性、等方性などに優れるものが好ましい。透明保護フィルムとしては、例えばポリエチレンテレフタレート、ポリエチレンナフタレート等のポリエステル系ポリマー、ジアセチルセルロース、トリアセチルセルロース等のセルロース系ポリマー、ポリカーボネート系ポリマー、ポリメチルメタクリレート等のアクリル系ポリマー等の透明ポリマーからなるフィルムがあげられる。またポリスチレン、アクリロニトリル・スチレン共重合体等のスチレン系ポリマー、ポリエチレン、ポリプロピレン、環状ないしノルボルネン構造を有するポリオレフィン、エチレン・プロピレン共重合体等のオレフィン系ポリマー、塩化ビニル系ポリマー、ナイロンや芳香族ポリアミド等のアミド系ポリマー等の透明ポリマーからなるフィルムもあげられる。さらにイミド系ポリマー、スルホン系ポリマー、ポリエーテルスルホン系ポリマー、ポリエーテルエーテルケトン系ポリマー、ポリフェニレンスルフィド系ポリマー、ビニルアルコール系ポリマー、塩化ビニリデン系ポリマー、ビニルブチラール系ポリマー、アリレート系ポリマー、ポリオキシメチレン系ポリマー、エポキシ系ポリマーや前記ポリマーのブレンド物等の透明ポリマーからなるフィルムなどもあげられる。特に光学的に複屈折の少ないものが好適に用いられる。偏光板の保護フィルムの観点よりは、トリアセチルセルロース、ポリカーボネート、アクリル系ポリマー、シクロオレフィン系樹脂、ノルボルネン構造を有するポリオレフィンなどが好適である。
【００９５】
また、特開２００１−３４３５２９号公報（ＷＯ０１／３７００７）に記載のポリマーフィルム、たとえば、（Ａ）側鎖に置換および／または非置換イミド基を有する熱可塑性樹脂と、（Ｂ）側鎖に置換および／非置換フェニルならびにニトリル基を有する熱可塑性樹脂を含有する樹脂組成物があげられる。具体例としてはイソブチレンとＮ−メチルマレイミドからなる交互共重合体とアクリロニトリル・スチレン共重合体とを含有する樹脂組成物のフィルムがあげられる。フィルムは樹脂組成物の混合押出品などからなるフィルムを用いることができる。
【００９６】
偏光特性や耐久性などの点より、特に好ましく用いることができる透明基板は、表面をアルカリなどでケン化処理したトリアセチルセルロースフィルムである。透明保護フィルムの厚さは、適宜に決定しうるが、一般には強度や取扱性等の作業性、薄層性などの点より１０〜５００μｍ程度である。特に２０〜３００μｍが好ましく、３０〜２００μｍがより好ましい。
【００９７】
また、透明保護フィルムは、できるだけ色付きがないことが好ましい。したがって、Ｒｔｈ＝［（ｎｘ＋ｎｙ）／２−ｎｚ］・ｄ（ただし、ｎｘ、ｎｙはフィルム平面内の主屈折率、ｎｚはフィルム厚方向の屈折率、ｄはフィルム厚みである）で表されるフィルム厚み方向の位相差値が−９０ｎｍ〜＋７５ｎｍである保護フィルムが好ましく用いられる。かかる厚み方向の位相差値（Ｒｔｈ）が−９０ｎｍ〜＋７５ｎｍのものを使用することにより、保護フィルムに起因する偏光板の着色（光学的な着色）をほぼ解消することができる。厚み方向位相差値（Ｒｔｈ）は、さらに好ましくは−８０ｎｍ〜＋６０ｎｍ、特に−７０ｎｍ〜＋４５ｎｍが好ましい。
【００９８】
前記透明保護フィルムは、表裏で同じポリマー材料からなる透明保護フィルムを用いてもよく、異なるポリマー材料等からなる透明保護フィルムを用いてもよい。
【００９９】
前記透明保護フィルムの偏光子を接着させない面には、ハードコート層や反射防止処理、スティッキング防止や、拡散ないしアンチグレアを目的とした処理を施したものであってもよい。
【０１００】
ハードコート処理は偏光板表面の傷付き防止などを目的に施されるものであり、例えばアクリル系、シリコーン系などの適宜な紫外線硬化型樹脂による硬度や滑り特性等に優れる硬化皮膜を透明保護フィルムの表面に付加する方式などにて形成することができる。反射防止処理は偏光板表面での外光の反射防止を目的に施されるものであり、従来に準じた反射防止膜などの形成により達成することができる。また、スティッキング防止処理は隣接層との密着防止を目的に施される。
【０１０１】
またアンチグレア処理は偏光板の表面で外光が反射して偏光板透過光の視認を阻害することの防止等を目的に施されるものであり、例えばサンドブラスト方式やエンボス加工方式による粗面化方式や透明微粒子の配合方式などの適宜な方式にて透明保護フィルムの表面に微細凹凸構造を付与することにより形成することができる。前記表面微細凹凸構造の形成に含有させる微粒子としては、例えば平均粒径が０．５〜５０μｍのシリカ、アルミナ、チタニア、ジルコニア、酸化錫、酸化インジウム、酸化カドミウム、酸化アンチモン等からなる導電性のこともある無機系微粒子、架橋又は未架橋のポリマー等からなる有機系微粒子などの透明微粒子が用いられる。表面微細凹凸構造を形成する場合、微粒子の使用量は、表面微細凹凸構造を形成する透明樹脂１００重量部に対して一般的に２〜５０重量部程度であり、５〜２５重量部が好ましい。アンチグレア層は、偏光板透過光を拡散して視角などを拡大するための拡散層（視角拡大機能など）を兼ねるものであってもよい。
【０１０２】
なお、前記反射防止層、スティッキング防止層、拡散層やアンチグレア層等は、透明保護フィルムそのものに設けることができるほか、別途光学層として透明保護層とは別体のものとして設けることもできる。
【０１０３】
前述した直線偏光素子には、液晶セル等の他部材と接着するための粘着層を設けることもできる。粘着層を形成する粘着剤は特に制限されないが、例えばアクリル系重合体、シリコーン系ポリマー、ポリエステル、ポリウレタン、ポリアミド、ポリエーテル、フッ素系やゴム系などのポリマーをベースポリマーとするものを適宜に選択して用いることができる。特に、アクリル系粘着剤の如く光学的透明性に優れ、適度な濡れ性と凝集性と接着性の粘着特性を示して、耐候性や耐熱性などに優れるものが好ましく用いうる。
【０１０４】
また上記に加えて、吸湿による発泡現象や剥がれ現象の防止、熱膨張差等による光学特性の低下や液晶セルの反り防止、ひいては高品質で耐久性に優れる液晶表示装置の形成性などの点より、吸湿率が低くて耐熱性に優れる粘着層が好ましい。
【０１０５】
粘着層は、例えば天然物や合成物の樹脂類、特に、粘着性付与樹脂や、ガラス繊維、ガラスビーズ、金属粉、その他の無機粉末等からなる充填剤や顔料、着色剤、酸化防止剤などの粘着層に添加されることの添加剤を含有していてもよい。また微粒子を含有して光拡散性を示す粘着層などであってもよい。
【０１０６】
粘着層の付設は、適宜な方式で行いうる。その例としては、例えばトルエンや酢酸エチル等の適宜な溶剤の単独物又は混合物からなる溶媒にベースポリマーまたはその組成物を溶解又は分散させた１０〜４０重量％程度の粘着剤溶液を調製し、それを流延方式や塗工方式等の適宜な展開方式で前記偏光子上に直接付設する方式、あるいは前記に準じセパレータ上に粘着層を形成してそれを光学素子上に移着する方式などがあげられる。粘着層は、各層で異なる組成又は種類等のものの重畳層として設けることもできる。粘着層の厚さは、使用目的や接着力などに応じて適宜に決定でき、一般には１〜５００μｍであり、５〜２００μｍが好ましく、特に１０〜１００μｍが好ましい。
【０１０７】
粘着層の露出面に対しては、実用に供するまでの間、その汚染防止等を目的にセパレータが仮着されてカバーされる。これにより、通例の取扱状態で粘着層に接触することを防止できる。セパレータとしては、上記厚さ条件を除き、例えばプラスチックフィルム、ゴムシート、紙、布、不織布、ネット、発泡シートや金属箔、それらのラミネート体等の適宜な薄葉体を、必要に応じシリコーン系や長鎖アルキル系、フッ素系や硫化モリブデン等の適宜な剥離剤でコート処理したものなどの、従来に準じた適宜なものを用いうる。
【０１０８】
なお、粘着層などの各層には、例えばサリチル酸エステル系化合物やべンゾフェノール系化合物、ベンゾトリアゾール系化合物やシアノアクリレート系化合物、ニッケル錯塩系化合物等の紫外線吸収剤で処理する方式などの方式により紫外線吸収能をもたせたものなどであってもよい。
【０１０９】
本発明の直線偏光素子は液晶表示装置等の各種装置の形成などに好ましく用いることができる。液晶表示装置の形成は、従来に準じて行いうる。すなわち液晶表示装置は一般に、液晶セルと光学素子、及び必要に応じての照明システム等の構成部品を適宜に組立てて駆動回路を組込むことなどにより形成されるが、本発明の直線偏光素子を用いる点を除いて特に限定はなく、従来に準じうる。液晶セルについても、例えばＴＮ型やＳＴＮ型、π型などの任意なタイプのものを用いうる。
【０１１０】
液晶セルの片側又は両側に前記直線偏光素子を配置した液晶表示装置や、照明システムにバックライトあるいは反射板を用いたものなどの適宜な液晶表示装置を形成することができる。その場合、本発明による直線偏光素子は液晶セルの片側又は両側に設置することができる。両側に直線偏光素子を設ける場合、それらは同じものであってもよいし、異なるものであってもよい。さらに、液晶表示装置の形成に際しては、例えば拡散板、アンチグレア層、反射防止膜、保護板、プリズムアレイ、レンズアレイシート、光拡散板、バックライトなどの適宜な部品を適宜な位置に１層又は２層以上配置することができる。
【０１１１】
また前記コレステリック液晶フィルムを用いた円偏光板（反射偏光子）は、偏光の選択反射の波長帯域が互いに重なっている少なくとも２層の反射偏光子（ａ）の間に、正面位相差（法線方向）がほぼゼロで、法線方向に対し３０°以上傾けて入射した入射光に対してλ／８以上の位相差を有する位相差層（ｂ）が配置された偏光素子システムに用いられる。なお、コレステリック液晶フィルムは、螺旋状ねじれ分子構造の最大ピッチと最小ピッチのいずれの側が位相差層（ｂ）の側であってもよいが、視角（視角がよい、色づきが小さい）点から、反射偏光子（ａ）を（最大ピッチ／最小ピッチ）と表示すれば、最大ピッチ／最小ピッチ／位相差層（ｂ）／最大ピッチ／最小ピッチのように配置するのが好ましい。また、λ／４板を組み合わせる場合には、反射偏光子（ａ）の最小ピッチ側がλ／４板側になるように配置するのが好ましい。
【０１１２】
前記偏光素子システム、すなわち、広帯域選択反射機能を有するコレステリック液晶積層体は、正面方向は円偏光反射／透過機能を有し、これを広帯域円偏光板として液晶表示装置に用いることができる。この場合には円偏光モードの液晶セル、例えばマルチドメインを有する透過型ＶＡモード液晶セルの光源側に配置することで円偏光板として用いることができる。
【０１１３】
位相差層（ｂ）は、正面方向の位相差がほぼゼロであり、法線方向から３０°の角度の入射光に対してλ／８以上の位相差を有するものである。正面位相差は垂直入射された偏光が保持される目的であるので、λ／１０以下であることが望ましい。
【０１１４】
斜め方向からの入射光に対しては効率的に偏光変換されるべく全反射させる角度などによって適宜決定される。例えば、法線からのなす角６０°程度で完全に全反射させるには６０°で測定したときの位相差がλ／２程度になるように決定すればよい。ただし、反射偏光子（ａ）による透過光は、反射偏光子自身のＣプレート的な複屈折性によっても偏光状態が変化しているため、通常挿入されるＣプレートのその角度で測定したときの位相差はλ／２よりも小さな値でよい。Ｃプレートの位相差は入射光が傾くほど単調に増加するため、効果的な全反射を３０°以上のある角度傾斜した時に起こさせる目安として３０°の角度の入射光に対してλ／８以上有すればよい。
【０１１５】
位相差層（ｂ）の材質は上記のような光学特性を有するものであれば、特に制限はない。例えば、可視光領域（３８０ｎｍ〜７８０ｎｍ） 以外に選択反射波長を有するコレステリック液晶のプラナー配向状態を固定したものや、棒状液晶のホメオトロピック配向状態を固定したもの、ディスコチック液晶のカラムナー配向やネマチック配向を利用したもの、負の１軸性結晶を面内に配向させたもの、２軸性配向したポリマーフィルムなどがあげられる。
【０１１６】
本発明において、可視光領域（３８０ｎｍ〜７８０ｎｍ）以外に選択反射波長を有するコレステリック液晶のプラナー配向状態を固定したＣプレートは、コレステリック液晶の選択反射波長としては、可視光領域に色付きなどがないことが望ましい。そのため、選択反射光が可視領域にない必要がある。選択反射はコレステリックのカイラルピッチと液晶の屈折率によって一義的に決定される。選択反射の中心波長の値は近赤外領域にあっても良いが、旋光の影響などを受けるため、やや複雑な現象が発生するため、３５０ｎｍ以下の紫外部にあることがより望ましい。コレステリック液晶層の形成については、前記した反射偏光子におけるコレステリック層形成と同様に行われる。
【０１１７】
本発明における、ホメオトロピック配向状態を固定したＣプレートは、高温でネマチック液晶性を示す液晶性熱可塑樹脂または液晶モノマーと必要に応じての配向助剤を電子線や紫外線などの電離放射線照射や熱により重合せしめた重合性液晶、またはそれらの混合物が用いられる。液晶性はリオトロピックでもサーモトロピック性のいずれでもよいが、制御の簡便性やモノドメインの形成しやすさの観点より、サーモトロピック性の液晶であることが望ましい。ホメオトロピック配向は、例えば、垂直配向膜（長鎖アルキルシランなど）を形成した膜上に前記複屈折材料を塗設し、液晶状態を発現させ固定することによって得られる。
【０１１８】
ディスコティック液晶を用いたＣプレートとしては、液晶材料として面内に分子の広がりを有したフタロシアニン類やトリフェニレン類化合物のごとく負の１軸性を有するディスコティック液晶材料を、ネマチック相やカラムナー相を発現させて固定したものである。負の１軸性無機層状化合物としては、たとえば、特開平６−８２７７７号公報などに詳しい。
【０１１９】
ポリマーフィルムの２軸性配向を利用したＣプレートは、正の屈折率異方性を有する高分子フィルムをバランス良く２軸延伸する方法、熱可塑樹脂をプレスする方法、平行配向した結晶体から切り出す方法などにより得られる。
【０１２０】
各層の積層は、重ね置いただけでも良いが、作業性や、光の利用効率の観点より各層を接着剤や粘着剤を用いて積層することが望ましい。その場合、接着剤または粘着剤は透明で、可視光域に吸収を有さず、屈折率は、各層の屈折率と可及的に近いことが表面反射の抑制の観点より望ましい。かかる観点より、例えば、アクリル系粘着剤などが好ましく用いうる。各層は、それぞれ別途配向膜状などでモノドメインを形成し、透光性基材へ転写などの方法によって順次積層していく方法や、接着層などを設けず、配向のために、配向膜などを適宜形成し、各層を順次直接形成して行くことも可能である。
【０１２１】
各層および（粘）接着層には、必要に応じて拡散度合い調整用に更に粒子を添加して等方的な散乱性を付与することや、紫外線吸収剤、酸化防止剤、製膜時のレベリング性付与の目的で界面活性剤などを適宜に添加することができる。
【０１２２】
本発明の偏光素子（コレステリック液晶積層体）は、円偏光反射／透過機能を有するが、これにλ／４板を組み合わせることで透過光線を直線偏光へ変換する直線偏光素子として用いることができる。λ／４板としては、前記同様のものを例示できる。
【０１２３】
λ／４板は単一材料による単層では特定の波長に対してのみ良好に機能するが、その他の波長に対しては波長分散特性上、λ／４板として機能が低下する問題がある。そこで、λ／２板と軸角度を規定して積層すれば可視光全域で実用上差し支えない程度の範囲で機能する広帯域λ／４板として用いることができる。この場合の各λ／４板、λ／２板は同一材料でも良いし上記記述のλ／４板と同様の手法で得られる別個の材料によって作製した物を組み合わせても良い。
【０１２４】
例えば、広帯域円偏光板にλ／４板（１４０ｎｍ）を積層し、この軸角度に対して１７．５度でλ／２板（２７０ｎｍ）を配置する。この場合の透過偏光軸はλ／４板の軸に対して１０度となる。この貼り合わせ角度は各位相差板の位相差値により変動するので上記の貼り合わせ角度に限定するものではない。
【０１２５】
前記直線偏光素子の透過軸に、吸収型偏光子をその透過軸方向を合わせて貼り合わせて用いられる。
【０１２６】
（拡散反射板の配置）
光源たる導光板の下側（液晶セルの配置面とは反対側）には拡散反射板の配置が望ましい。平行光化フィルムにて反射される光線の主成分は斜め入射成分であり、平行光化フィルムにて正反射されてバックライト方向へ戻される。ここで背面側の反射板が正反射性が高い場合には反射角度が保存され、正面方向に出射できずに損失光となる。従って反射戻り光線の反射角度を保存せず、正面方向へ散乱反射成分を増大させるため拡散反射板の配置が望ましい。
【０１２７】
（拡散板の配置）
本発明における平行光化フィルムとバックライト光源の間には適当な拡散板を設置することも望ましい。斜め入射し、反射された光線をバックライト導光体近傍にて散乱させ、その一部を垂直入射方向へ散乱せしめることで光の再利用効率が高まるためである。
【０１２８】
用いられる拡散板は表面凹凸形状による物の他、屈折率が異なる微粒子を樹脂中に包埋する等の方法で得られる。この拡散板は平行光化フィルムとバックライト間に挟み込んでも良いし、平行光化フィルムに貼り合わせてもよい。
【０１２９】
平行光化フィルムを貼り合わせた液晶セルをバックライトと近接して配置する場合、フィルム表面とバックライトの隙間でニュートンリングが生じる恐れがあるが、本発明における平行光化フィルムの導光板側表面に表面凹凸を有する拡散板を配置することによってニュートンリングの発生を抑制することができる。また、本発明における平行光化フィルムの表面そのものに凹凸構造と光拡散構造を兼ねた層を形成しても良い。
【０１３０】
（視野角拡大フィルムの配置）
本発明の液晶表示装置における視野角拡大は、平行光化されたバックライトと組み合わされた、液晶表示装置から得られる正面近傍の良好な表示特性の光線を拡散し、全視野角内で均一で良好な表示特性を得ることによって得られる。
【０１３１】
ここで用いられる視野角拡大フィルムは実質的に後方散乱を有さない拡散板が用いられる。拡散板は、拡散粘着材として設けることができる。配置場所は液晶表示装置の視認側であるが偏光板の上下いずれでも使用可能である。ただし画素のにじみ等の影響やわずかに残る後方散乱によるコントラスト低下を防止するために偏光板〜液晶セル間など、可能な限りセルに近い層に設けることが望ましい。またこの場合には実質的に偏光を解消しないフィルムが望ましい。例えば特開２０００−３４７００６号公報、特開２０００−３４７００７号公報に開示されているような微粒子分散型拡散板が好適に用いられる。
【０１３２】
偏光板より外側に視野角拡大フィルムを位置する場合には液晶層−偏光板まで平行光化された光線が透過するのでＴＮ液晶セルの場合は特に視野角補償位相差板を用いなくともよい。ＳＴＮ液晶セルの場合には正面特性のみ良好に補償した位相差フィルムを用いるだけでよい。この場合には視野角拡大フィルムが空気表面を有するので表面形状による屈折効果によるタイプの採用も可能である。
【０１３３】
一方で偏光板と液晶層間に視野角拡大フィルムを挿入する場合には偏光板を透過する段階では拡散光線となっている。ＴＮ液晶の場合、偏光子そのものの視野角特性は補償する必要がある。この場合には偏光子の視野角特性を補償する位相差板を偏光子と視野角拡大フィルムの間に挿入する必要がある。ＳＴＮ液晶の場合にはＳＴＮ液晶の正面位相差補償に加えて偏光子の視野角特性を補償する位相差板を挿入する必要がある。
【０１３４】
従来から存在するマイクロレンズアレイフィルムやホログラムフィルムのように、内部に規則性構造体を有する視野角拡大フィルムの場合、液晶表示装置のブラックマトリクスや従来のバックライトの平行光化システムが有するマイクロレンズアレイ／プリズムアレイ／ルーバー／マイクロミラーアレイ等の微細構造と干渉しモアレを生じやすかった。しかし本発明における平行光化フィルムは面内に規則性構造が視認されず、出射光線に規則性変調が無いので視野角拡大フィルムとの相性や配置順序を考慮する必要はない。従って視野角拡大フィルムは液晶表示装置の画素ブラックマトリクスと干渉／モアレを発生しなければ特に制限はなく選択肢は広い。
【０１３５】
本発明においては視野角拡大フィルムとして実質的に後方散乱を有さない、偏光を解消しない、特開２０００−３４７００６号公報、特開２０００−３４７００７号公報に記載されているような光散乱板で、ヘイズ８０％〜９０％の物が好適に用いられる。その他、ホログラムシート、マイクロプリズムアレイ、マイクロレンズアレイ等、内部に規則性構造を有していても液晶表示装置の画素ブラックマトリクスと干渉／モアレを形成しなければ使用可能である。
【０１３６】
なお、液晶表示装置には、常法に従って、各種の光学層等が適宜に用いられて作製される。
【０１３７】
【実施例】
以下、実施例、比較例をあげて本発明を説明するが、本発明はこれらの実施例に限定されるものではない。
【０１３８】
実施例１
光重合性メソゲン化合物（重合性ネマチック液晶モノマー，上記化４の化合物（１），モル吸光係数は、２２０ｄｍ^３ ｍｏｌ^−１ｃｍ^−１＠３６５ｎｍ。）９４．８重量部および重合性カイラル剤（ＢＡＳＦ社製ＬＣ７５６）５．２ 重量部および溶媒（シクロペンタノン）を選択反射中心波長が５５０ｎｍとなるよう調整配合した溶液に、その固形分に対し、光重合開始剤（チバスペシャルティケミカルズ社製，イルガキュア９０７）を３重量％添加した塗工液（固形分含有量３０重量％）を調製した。当該塗工液を、延伸ポリエチレンテレフタレートフィルム（配向基材）上にワイヤーバーを用いて乾燥後の厚みで７μｍとなるように塗設し、溶媒を１００℃で２分間乾燥させた。得られた膜に、配向基材側から９０℃の空気雰囲気下で、表１に示す１回目〜５回目の紫外線照射を順次に行った。
【０１３９】
次いで、５０℃の窒素雰囲気下で配向基材側から第３紫外線照射を６０ｍＷ／ｃｍ^２ で、１０秒間行い、選択波長が４１０〜９６５ｎｍの広帯域コレステリック液晶フィルムを得た。広帯域コレステリック液晶フィルムの反射スペクトルを図４に示す。
【０１４０】
得られた広帯域コレステリック液晶フィルム（円偏光反射板）の上部へ、透光性の接着剤を用いて、負の２軸性位相差板を転写した。この負の２軸性位相差板は、下記方法により得た。すなわち、光重合性ネマチック液晶モノマー（ＢＡＳＦ社製，ＬＣ２４２）９３重量部、重合性カイラル剤（ＢＡＳＦ社製ＬＣ７５６）７重量部に３０重量％濃度となるように溶媒としてシクロヘキサノンを加え、また選択反射中心波長が３５０ｎｍとなるよう調整配合した後、前述の固形分に対して光重合開始剤としてイルガキュア９０７を５重量％添加した塗工液を調製し、上記溶液を、延伸ポリエチレンテレフタレート基材にワイヤーバーを用いて乾燥後の厚みで４μｍとなるように塗設し、溶媒を１００℃、２分間で乾燥した。その後、一度この液晶モノマーの等方性転移温度まで温度を上げた後、徐々に冷却して、均一な配向状態を有した層を形成した。得られた層に、５０ｍＷ／ｃｍ^２ 、５秒間行い配向状態を固定することで得た。この負の２軸性位相差板の位相差を測定したところ５５０ｎｍの波長の光に対して正面方向では２ｎｍ、３０°傾斜させて測定したときの位相差は１２０ｎｍであった。なお、位相差の測定は、Ｏｊｉ Ｓｃｉｅｎｔｉｆｉｃ Ｉｎｓｔｒｕｍｅｎｔｓ社製のＫＯＢＲＡ−２１ＡＤＨにより行った。
【０１４１】
さらにこの上部に同じく透光性の接着剤を用いて、上記同様の円偏光反射板を転写して積層し、偏光素子を得た。得られた偏光素子に、ポリカーボネートフィルムを一軸延伸して得られたλ／４板（正面位相差１４０ｎｍ）を接着して直線偏光素子を得た。この直線偏光素子に、偏光板（日東電工社製，ＴＥＧ１４６５ＤＵ）を透過軸方向が一致するように貼り合わせ、偏光板一体型偏光素子を得た。
【０１４２】
実施例２
実施例１で調製した塗工液を、延伸ポリエチレンテレフタレートフィルム（配向基材）上にワイヤーバーを用いて乾燥後の厚みで７μｍとなるように塗設し、溶媒を１００℃で２分間乾燥させた。得られた膜に、配向基材側から９０℃の空気雰囲気下で、表１に示す１回目〜４回目の紫外線照射を順次に行った。
【０１４３】
次いで、５０℃の窒素雰囲気下で配向基材側から第３紫外線照射を６０ｍＷ／ｃｍ^２ で、１０秒間行い、選択波長が４１５〜９３０ｎｍの広帯域コレステリック液晶フィルムを得た。広帯域コレステリック液晶フィルムの反射スペクトルを図５に示す。
【０１４４】
得られた広帯域コレステリック液晶フィルム（円偏光反射板）の上部へ、透光性の接着剤を用いて、実施例１と同様の負の２軸性位相差板を転写した。さらにこの上部に同じく透光性の接着剤を用いて、上記同様の円偏光反射板を転写して積層し、偏光素子を得た。得られた偏光素子に、ポリカーボネートフィルムを一軸延伸して得られたλ／４板（正面位相差１４０ｎｍ）を接着して直線偏光素子を得た。さらに、そのλ／４板上に、ポリカーボネートフィルムを一軸延伸して得られたλ／２板（正面位相差２７０ｎｍ）を接着して直線偏光素子を得た。この直線偏光素子に、偏光板（日東電工社製，ＴＥＧ１４６５ＤＵ）を透過軸方向が一致するように貼り合わせ、偏光板一体型偏光素子を得た。これらの積層は、λ／４板、λ／２板の延伸軸（遅相軸）と偏光板の延伸軸（吸収軸）の角度が、図３に示すように行った。
【０１４５】
実施例３
光重合性メソゲン化合物（重合性ネマチック液晶モノマー，上記化４の化合物（１），モル吸光係数は、２２０ｄｍ^３ ｍｏｌ^−１ｃｍ^−１＠３６５ｎｍ。）９４．８重量部および重合性カイラル剤（ＢＡＳＦ社製ＬＣ７５６）５．２ 重量部および溶媒（シクロペンタノン）を選択反射中心波長が５５０ｎｍとなるよう調整配合した溶液に、その固形分に対し、光重合開始剤（チバスペシャルティケミカルズ社製，イルガキュア３６９）を０．３重量％添加した塗工液（固形分含有量３０重量％）を調製した。当該塗工液を、延伸ポリエチレンテレフタレートフィルム（配向基材）上にワイヤーバーを用いて乾燥後の厚みで７μｍとなるように塗設し、溶媒を１００℃で２分間乾燥させた。得られた膜に、配向基材側から９０℃の空気雰囲気下で、表１に示す１回目〜５回目の紫外線照射を順次に行った。
【０１４６】
次いで、５０℃の窒素雰囲気下で配向基材側から第３紫外線照射を６０ｍＷ／ｃｍ^２ で、１０秒間行い、選択波長が４２０〜８９０ｎｍの広帯域コレステリック液晶フィルムを得た。広帯域コレステリック液晶フィルムの反射スペクトルを図６に示す。
【０１４７】
得られた広帯域コレステリック液晶フィルム（円偏光反射板）の上部へ、透光性の接着剤を用いて、実施例１と同様の負の２軸性位相差板を転写した。さらにこの上部に同じく透光性の接着剤を用いて、上記同様の円偏光反射板を転写して積層し、偏光素子を得た。得られた偏光素子に、ポリカーボネートフィルムを二軸延伸して得られたλ／４板（正面位相差１２５ｎｍ，Ｎｚ係数が−１．０）を接着して直線偏光素子を得た。この直線偏光素子に、偏光板（日東電工社製，ＴＥＧ１４６５ＤＵ）を透過軸方向が一致するように貼り合わせ、偏光板一体型偏光素子を得た。
【０１４８】
比較例１
実施例１で調製した塗工液を、延伸ポリエチレンテレフタレートフィルム（配向基材）上にワイヤーバーを用いて乾燥後の厚みで５μｍとなるように塗設し、溶媒を１００℃で２分間乾燥させた。得られた膜に、配向基材側から６０℃の空気雰囲気下で第１紫外線照射を５０ｍＷ／ｃｍ^２ で、１０秒間行った。次いで、５０℃の窒素雰囲気下で配向基材側から紫外線照射を６０ｍＷ／ｃｍ^２ で、１０秒間行い、選択波長が４３５〜８３５ｎｍの広帯域コレステリック液晶フィルムを得た。広帯域コレステリック液晶フィルムの反射スペクトルを図７に示す。
【０１４９】
得られた広帯域コレステリック液晶フィルム（円偏光反射板）の上部へ、透光性の接着剤を用いて、実施例１と同様の負の２軸性位相差板を転写した。さらにこの上部に同じく透光性の接着剤を用いて、上記同様の円偏光反射板を転写して積層し、偏光素子を得た。得られた偏光素子に、ポリカーボネートフィルムを一軸延伸して得られたλ／４板（正面位相差１４０ｎｍ）を接着して直線偏光素子を得た。この直線偏光素子に、偏光板（日東電工社製，ＴＥＧ１４６５ＤＵ）を透過軸方向が一致するように貼り合わせ、偏光板一体型偏光素子を得た。
【０１５０】
比較例２
実施例１で調製した塗工液を、延伸ポリエチレンテレフタレートフィルム（配向基材）上にワイヤーバーを用いて乾燥後の厚みで７μｍとなるように塗設し、溶媒を１００℃で２分間乾燥させた。得られた膜に、配向基材側から４０℃の空気雰囲気下で第１紫外線照射を４０ｍＷ／ｃｍ^２ で、１．２秒間行った。さらに９０℃で２０秒間熱処理を行った。次いで、５０℃の窒素雰囲気下で配向基材側から紫外線照射を６０ｍＷ／ｃｍ^２ で、１０秒間行い、選択波長が４１５〜７１０ｎｍの広帯域コレステリック液晶フィルムを得た。広帯域コレステリック液晶フィルムの反射スペクトルを図８に示す。
【０１５１】
得られた広帯域コレステリック液晶フィルム（円偏光反射板）の上部へ、透光性の接着剤を用いて、実施例１と同様の負の２軸性位相差板を転写した。さらにこの上部に同じく透光性の接着剤を用いて、上記同様の円偏光反射板を転写して積層し、偏光素子を得た。得られた偏光素子に、ポリカーボネートフィルムを一軸延伸して得られたλ／４板（正面位相差１４０ｎｍ）を接着して直線偏光素子を得た。この直線偏光素子に、偏光板（日東電工社製，ＴＥＧ１４６５ＤＵ）を透過軸方向が一致するように貼り合わせ、偏光板一体型偏光素子を得た。
【０１５２】
比較例３
実施例１で調製した塗工液を、延伸ポリエチレンテレフタレートフィルム（配向基材）上にワイヤーバーを用いて乾燥後の厚みで７μｍとなるように塗設し、溶媒を１００℃で２分間乾燥させた。得られた膜に、配向基材側から９０℃の空気雰囲気下で、表１に示す１回目〜５回目の紫外線照射を順次に行い、選択波長が４１０〜９６５ｎｍの広帯域コレステリック液晶フィルムを得た。広帯域コレステリック液晶フィルムの反射スペクトルを図９に示す。
【０１５３】
得られた広帯域コレステリック液晶フィルム（円偏光反射板）の上部へ、透光性の接着剤を用いて、実施例１と同様の負の２軸性位相差板を転写した。さらにこの上部に同じく透光性の接着剤を用いて、上記同様の円偏光反射板を転写して積層し、偏光素子を得た。得られた偏光素子に、ポリカーボネートフィルムを一軸延伸して得られたλ／４板（正面位相差１４０ｎｍ）を接着して直線偏光素子を得た。この直線偏光素子に、偏光板（日東電工社製，ＴＥＧ１４６５ＤＵ）を透過軸方向が一致するように貼り合わせ、偏光板一体型偏光素子を得た。
【０１５４】
（液晶表示装置）
各例で得られた偏光板一体型偏光素子をＴＦＴ−ＬＣＤの下板として用い、一方、上板側にはアクリル系粘着材（厚み２５μｍ，屈折率１．４７）中に球状シリカ粒子（屈折率１．４４，直径４μｍ）を２０重量％包埋した光散乱性粘着材（ヘイズ８０％）を用いて偏光板（日東電工社製，ＴＥＧ１４６５ＤＵ）を積層した。
【０１５５】
また、下面に微細プリズム構造を有した導光体の側面に直径約３ｍｍの冷陰極管を配置し、銀蒸着ポリエチレンテレフタレートフィルムから成る光源ホルダでカバーした。導光板の下面には銀蒸着ポリエチレンテレフタレートフィルム反射板を配置し、導光板上面にはスチレンビーズから成る散乱層を表面に形成したポリエチレンテレフタレートフィルムを配置した。これを、光源として、偏光板一体型偏光素子の下側に配置した。
【０１５６】
実施例１、３、比較例１〜３の偏光板一体型偏光素子を用いた場合が図１であり、実施例２の偏光板一体型偏光素子を用いた場合が図２である。
【０１５７】
＜評価方法＞
上記で得られた広帯域コレステリック液晶フィルム（円偏光反射板）、偏光板一体型偏光素子について下記評価を行った。結果を表１に示す。なお、実施例および比較例の各工程の条件も表１に示す。
【０１５８】
（選択反射波長帯域および帯域巾（△λ））
広帯域コレステリック液晶フィルムの反射スペクトルを分光光度計（大塚電子株式会社製，瞬間マルチシステムＭＣＰＤ２０００）にて測定し、選択反射波長帯域および半値巾△λを求めた。半値巾△λは、最大反射率の半分の反射率における反射帯域とした。
【０１５９】
（ピッチ変化）
広帯域コレステリック液晶フィルムの紫外線照射面近傍（紫外線照射面から１μｍ下層）と、空気界面近傍（空気界面から１μｍ下層）およびその中間のピッチ長を断面ＴＥＭ写真により測定した。
【０１６０】
（信頼性）
広帯域コレステリック液晶フィルムを、８０℃、および６０℃で９０％ＲＨの信頼性試験にそれぞれ５００時間投入したときに、表面に粉状物質の析出が認められるか否かを評価した。
【０１６１】
○：析出物なし。
×：析出物あり。
【０１６２】
（正面輝度）
偏光板一体型偏光素子の偏光板側が上になるようにドット印刷型バックライト上に配置して輝度計（ＴＯＰＣＯＮ製，ＢＭ−７）により評価した。
【０１６３】
（斜めの色調変化）
液晶表示装置の斜めの色調変化を、ＥＬＤＩＭ社製視野角測定器ＥＺ−ＣＯＮＴＲＡＳＴにより下記基準で評価した。
Δｘｙ＝（（ｘ_０ −ｘ_１ ）^２ ＋（ｙ_０ −ｙ_１ ）^２ ）^０．５
正面色度（ｘ_０ ，ｙ_０ ）、斜め°±６０°からの色度（ｘ_１ ，ｙ_１ ）
良好：視野角６０°における色調変化Δｘｙが０．０４未満。
不良：視野角６０°における色調変化Δｘｙが０．０４以上。
【０１６４】
【表１】

実施例では、長波長域を含む広帯域に選択反射波長を有するコレステリック液晶フィルムが得られている。当該コレステリック液晶フィルムは、信頼性が高くまた、これを円偏光板として用いた偏光素子は輝度向上特性にも優れている。また、当該偏光素子を用いた液晶表示装置は、諧調反転しない領域の表示情報を斜め方向に光拡散で振り分けたため、斜め方向からの色調変化や諧調反転が生じにくい視野角の広い液晶表示装置を得ることができる。
【図面の簡単な説明】
【図１】実施例１、３、比較例１〜３の偏光板一体型偏光素子を用いた視野角拡大液晶表示装置の概念図である。
【図２】実施例２の偏光板一体型偏光素子を用いた視野角拡大液晶表示装置の概念図である。
【図３】実施例２の偏光板一体型偏光素子における各層の軸角度を表す図である。
【図４】実施例１で作製したコレステリック液晶フィルムの反射スペクトルである。
【図５】実施例２で作製したコレステリック液晶フィルムの反射スペクトルである。
【図６】実施例３で作製したコレステリック液晶フィルムの反射スペクトルである。
【図７】比較例１で作製したコレステリック液晶フィルムの反射スペクトルである。
【図８】比較例２で作製したコレステリック液晶フィルムの反射スペクトルである。
【図９】比較例３で作製したコレステリック液晶フィルムの反射スペクトルである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a broadband cholesteric liquid crystal film. The broadband cholesteric liquid crystal film of the present invention is useful as a circularly polarizing plate (reflection type polarizer). Further, the present invention relates to a linear polarizing element, a lighting device, and a liquid crystal display device using the circular polarizing plate.
[0002]
[Prior art]
Generally, a liquid crystal display has a structure in which liquid crystal is injected between glass plates on which transparent electrodes are formed, and polarizers are arranged before and after the glass plates. A polarizer used for such a liquid crystal display is manufactured by adsorbing iodine, a dichroic dye, or the like on a polyvinyl alcohol film and stretching the same in a certain direction. The polarizer thus manufactured per se absorbs light oscillating in one direction and passes only light oscillating in the other direction to produce linearly polarized light. Therefore, the efficiency of the polarizer cannot theoretically exceed 50%, which is the largest factor that lowers the efficiency of the liquid crystal display. Also, due to this absorbed light, if the output of the light source is increased to a certain degree or more, the liquid crystal display device will break down the polarizer due to the heat generated by the heat conversion of the absorbed light, or display the liquid crystal layer inside the cell due to the thermal effect. This has caused adverse effects such as deterioration of quality.
[0003]
A cholesteric liquid crystal having a function of separating circularly polarized light has a selective reflection characteristic in which the direction of rotation of the liquid crystal helix coincides with the direction of circular polarization, and reflects only circularly polarized light whose wavelength is the helical pitch of the liquid crystal. By using this selective reflection characteristic, only specific circularly polarized light of natural light in a certain wavelength band is transmitted and separated, and the rest is reflected and reused, whereby a highly efficient polarizing film can be manufactured. At this time, the transmitted circularly polarized light is converted into linearly polarized light by passing through a λ / 4 wavelength plate, and the direction of the linearly polarized light is aligned with the transmission direction of the absorption polarizer used in the liquid crystal display, thereby achieving high transmittance. A liquid crystal display device can be obtained. That is, when a cholesteric liquid crystal film is used as a linear polarizing element in combination with a λ / 4 wavelength plate, there is theoretically no loss of light. Therefore, when a conventional absorption polarizer that absorbs 50% of light is used alone. In comparison, a two-fold improvement in brightness can be obtained in theory.
[0004]
However, the selective reflection characteristic of the cholesteric liquid crystal is limited to only a specific wavelength band, and it has been difficult to cover the entire visible light range. The selective reflection wavelength range width △ λ of cholesteric liquid crystal is
Δλ = 2λ · (ne−no) / (ne + no)
no: refractive index of cholesteric liquid crystal molecules to normal light
ne: refractive index of cholesteric liquid crystal molecules to extraordinary light
λ: center wavelength of selective reflection
And depends on the molecular structure of the cholesteric liquid crystal itself. From the above equation, if the value of ne-no is increased, the width of the selective reflection wavelength region Δλ can be increased, but the value of ne-no is usually 0.3 or less. When this value is increased, other functions (alignment characteristics, liquid crystal temperature, etc.) of the liquid crystal become insufficient, and practical use has been difficult. Accordingly, in practice, the selective reflection wavelength region width Δλ is at most about 150 nm. Most of practically usable cholesteric liquid crystals have a thickness of only about 30 to 100 nm.
[0005]
The selective reflection center wavelength λ is
λ = (ne + no) P / 2
P: helical pitch length required for one turn of cholesteric liquid crystal
If the pitch is constant, it depends on the average refractive index of the liquid crystal molecules and the pitch length.
[0006]
Therefore, in order to cover the entire visible light region, a plurality of layers having different selective reflection center wavelengths are laminated, or the pitch length is continuously changed in the thickness direction to form the existence distribution of the selective reflection center wavelength itself. Was.
[0007]
For example, there is a method of continuously changing the pitch length in the thickness direction (for example, see Patent Literature 1, Patent Literature 2, Patent Literature 3, and Patent Literature 4). In this method, when the cholesteric liquid crystal composition is cured by ultraviolet light exposure, the difference in the exposure intensity between the exposed surface side and the outgoing surface side, and the difference in the polymerization rate, the composition ratio of the liquid crystal compositions with different reaction rates. The change is provided in the thickness direction.
[0008]
The point of this method is to take a large difference in exposure intensity between the exposure surface side and the emission surface side. Therefore, in many cases of the above-mentioned prior art examples, a method of mixing an ultraviolet absorber into a liquid crystal composition, generating absorption in a thickness direction, and amplifying a difference in exposure amount due to an optical path length has been adopted. .
[0009]
However, in the method of continuously changing the pitch length as disclosed in Patent Document 1, the thickness of the liquid crystal layer required to exhibit the function is required to be about 15 to 20 μm, and in addition to the problem of precise coating of the liquid crystal layer, expensive liquid crystal is required. Cost was inevitable because of the need for a large amount of Further, the exposure time is required to be about 1 to 60 minutes, and a long production line having an exposure line length of 10 to 600 m is required to obtain a line speed of 10 m / min. If the line speed is reduced, the line length can be reduced, but a reduction in the production speed cannot be avoided.
[0010]
This is because, as described in Patent Document 1, the cholesteric pitch is changed by a composition ratio change due to mass transfer due to a difference in ultraviolet exposure intensity in the thickness direction to change the pitch length in the thickness direction and a polymerization rate difference. This is because it is difficult to form a quick pitch change due to a theoretical problem to be controlled. In Patent Document 1, since the pitch length is different by about 100 nm between the short pitch side and the long pitch side, it is necessary to largely change the composition ratio. In order to realize this, a considerable liquid crystal thickness, weak ultraviolet irradiation and a long exposure time are required. is necessary.
[0011]
In Patent Document 3, since the mobility of the substance that changes the pitch is better than the material example used in Patent Document 1, a film can be formed with an exposure amount of about 1 minute. However, even in this case, a thickness of 15 μm is required.
[0012]
In Patent Document 2, the temperature conditions of the primary exposure and the secondary exposure are changed, and the time required for the composition ratio to change in the thickness direction is separately provided in a dark place. However, this method covers substantially the entire visible light region. In this case, the waiting time for mass transfer due to the temperature change needs to be about 120 minutes.
[0013]
In the method of continuously changing the pitch length as in Patent Document 4, the thickness of the liquid crystal layer required to exhibit the function is required to be about 15 to 20 μm, and in addition to the problem of precise coating of the liquid crystal layer, a large amount of expensive liquid crystal is required. In order to do so, the cost was inevitable. Further, in Patent Document 4, when the cholesteric liquid crystal composition is cured by ultraviolet exposure from the side opposite to the substrate (air interface side), the composition is changed by giving a difference in exposure intensity between the exposed surface side and the emission surface side due to oxygen inhibition. The ratio change is changed in the thickness direction.
[0014]
However, in FIG. 4 in Example 1 of Patent Document 4, although the selective reflection wavelength is broadened, the slopes of the transmittance curve on the short wavelength end side and the long wavelength side are both gentle, so that the cover can cover substantially the entire visible light range. Has not been reached. Further, in FIG. 6 in Example 2 of Patent Document 4, although the slopes at both wavelength ends are steep, the band itself is narrow.
[0015]
In particular, when this type of polarizing element is used in a liquid crystal display device, it is necessary to secure sufficiently flat transmittance / reflectance characteristics for three wavelengths of 435 nm, 545 nm, and 615 nm, which are emission spectra of a backlight light source. . In each case, the broadening range obtained by the methods of Examples 1 and 2 described in Patent Document 4 was insufficient to cover the emission line spectra at 435 nm and 615 nm. In such a case, it is difficult to obtain a white color tone of the transmitted light, and it is not used for applications such as a liquid crystal display device.
[0016]
[Patent Document 1]
JP-A-6-281814
[0017]
[Patent Document 2]
Japanese Patent No. 3272668
[0018]
[Patent Document 3]
JP-A-11-248943
[0019]
[Patent Document 4]
JP-A-2002-286935
[0020]
[Problems to be solved by the invention]
With respect to the above problem, the present applicant has filed Japanese Patent Application No. 2001-339632. In this application, the liquid crystal composition applied to the alignment substrate is irradiated with ultraviolet light from the alignment substrate. Thus, the polymerization is started from the surface which is hardly affected by the polymerization inhibition by oxygen in contact with the alignment base material, and the ultraviolet irradiation intensity distribution is formed in the thickness direction by utilizing the absorption by the molar absorption coefficient of the liquid crystal layer. By reducing the effective irradiation amount of ultraviolet rays on the air surface side, which is greatly affected by the above, a gradient of the liquid crystal reaction speed and the distribution of the composition concentration which are larger than those of the related art are formed. By making a difference between the exposure intensity on the exposure surface side and the exposure intensity on the emission surface side in this way, a large change in the cholesteric pitch length in the thickness direction was successfully achieved. In this application, a selective reflection wavelength bandwidth as wide as 296 nm at the maximum was obtained.
[0021]
In the case of the aforementioned application, a wavelength band of about 400 to 700 nm is covered. These wavelength bands cover the light source spectrum. In these, good circularly polarized light reflection characteristics can be obtained near normal incidence. On the other hand, at oblique incidence, the wavelength band was not sufficient. The selective reflection wavelength λ at oblique incidence is
λ = npcos ｛sin^-1(Sin θ / n)｝
n = average refractive index of liquid crystal
p = cholesteric pitch length
θ = incident angle
Therefore, when the light is obliquely incident, the selective reflection wavelength shifts to a shorter wavelength side than when the light is vertically incident. Therefore, in order to function effectively with respect to obliquely incident light, it is necessary to function in a long wavelength region.
[0022]
An object of the present invention is to provide a method capable of manufacturing a broadband cholesteric liquid crystal film having a broadband reflection band even in a long wavelength region.
[0023]
Another object of the present invention is to provide a circularly polarizing plate using a broadband cholesteric liquid crystal film obtained by the production method. Further, another object is to provide a linear polarizing element, a lighting device, and a liquid crystal display device using the circular polarizing plate.
[0024]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that a broadband cholesteric liquid crystal film that can achieve the above object can be obtained by the following manufacturing method, and have completed the present invention. That is, the present invention is as follows.
[0025]
1. A step of applying a liquid crystal mixture containing a polymerizable mesogen compound (A) and a polymerizable chiral agent (B) to an alignment substrate, and a step of irradiating the liquid crystal mixture with ultraviolet rays to carry out polymerization and curing; A method for producing a broadband cholesteric liquid crystal film having
The ultraviolet polymerization step,
In a state where the liquid crystal mixture is in contact with a gas containing oxygen, at a temperature of 20 ° C. or more, 1 to 200 mW / cm²  UV irradiation intensity, in the range of 0.2 to 30 seconds, every time the number of times increases, the UV irradiation intensity is low, and while increasing the UV irradiation time, UV irradiation from the alignment substrate side three times or more Irradiation step (1),
Next, a method for producing a broadband cholesteric liquid crystal film, comprising a step (2) of irradiating ultraviolet rays in the absence of oxygen.
[0026]
2. 2. The method for manufacturing a broadband cholesteric liquid crystal film according to the above item 1, wherein the pitch length of the cholesteric liquid crystal film is changed so as to continuously narrow from the alignment substrate side.
[0027]
3. 3. The broadband cholesteric liquid crystal film according to the above 1 or 2, wherein the polymerizable mesogen compound (A) has one polymerizable functional group, and the polymerizable chiral agent (B) has two or more polymerizable functional groups. Manufacturing method.
[0028]
4. The molar extinction coefficient of the polymerizable mesogen compound (A) is 50 to 500 dm.³  mol^-1cm^-14. The method for producing a broadband cholesteric liquid crystal film according to any one of the above items 1 to 3, wherein the thickness is 365 nm.
[0029]
5. The polymerizable mesogen compound (A) has the following general formula (1):
Embedded image

(However, R₁  Represents a hydrogen atom or a methyl group. n represents an integer of 1 to 5. 5. The method for producing a broadband cholesteric liquid crystal film according to any one of the above items 1 to 4, wherein the compound is a compound represented by the following formula:
[0030]
6. A circularly polarizing plate using a broadband cholesteric liquid crystal film obtained by the production method according to any one of the above 1 to 5.
[0031]
7. Between at least two layers of reflective polarizers (a) in which the wavelength bands of polarized light selective reflection overlap each other;
A phase difference layer (b) having a front phase difference (normal direction) of substantially zero and having a phase difference of λ / 8 or more with respect to incident light incident at an angle of 30 ° or more with respect to the normal direction is provided. A polarizing element,
A polarizing element, wherein the reflective polarizer (a) is the circularly polarizing plate described in the above item 6.
[0032]
8. 8. The polarizing element according to the above item 7, wherein the selective reflection wavelengths of at least two layers of the reflective polarizer (a) overlap each other in a wavelength range of 550 nm ± 10 nm.
[0033]
9. A phase difference layer (b) in which the planar orientation of a cholesteric liquid crystal phase having a selective reflection wavelength range other than the visible light range is fixed,
Fixed homeotropic alignment state of rod-shaped liquid crystal,
Discotic liquid crystal with a fixed nematic or columnar phase alignment state,
Biaxially oriented polymer film, or
9. The polarizing element according to the above item 7 or 8, wherein the inorganic layered compound having a negative uniaxial property is fixed so as to have an optical axis in a direction normal to the surface.
[0034]
10. 7. A linearly polarizing element, characterized in that a λ / 4 plate is laminated on the circularly polarizing plate described in the above item 6 or the polarizing element described in any of the above items 7 to 9, so that linearly polarized light can be obtained by transmission.
[0035]
11. 11. The linear polarizing element according to the above item 10, obtained by laminating a cholesteric liquid crystal film as a circular polarizing plate on a λ / 4 plate so that the pitch length is continuously narrowed.
[0036]
12. 12. The linear polarizing element according to the above item 10 or 11, wherein the λ / 4 plate is a retardation plate having a viewing angle improved by performing biaxial stretching to correct a phase difference of obliquely incident light.
[0037]
13. 12. The linear polarizing element according to the above item 10 or 11, wherein the λ / 4 plate is a liquid crystal polymer type retardation plate obtained by applying and fixing a nematic liquid crystal or a smectic liquid crystal.
[0038]
14． When the λ / 4 plate has an in-plane main refractive index of nx and ny and a thickness direction main refractive index of nz, the Nz coefficient defined by the formula: (nx−nz) / (nx−ny) becomes 14. The linear polarizing element according to any one of 10 to 13 above, which satisfies -0.5 to -2.5.
[0039]
15. 15. A linear polarization element, wherein a λ / 2 plate is further laminated on the λ / 4 plate of the linear polarization element according to any one of the above items 10 to 14.
[0040]
16. 16. A linear polarizing element, wherein an absorption polarizer having a transmission axis aligned with the transmission axis of the linear polarizing element according to any one of the above 10 to 15 is laminated on the λ / 4 plate side of the linear polarizing element. .
[0041]
17. The surface light source having a reflective layer on the back side has the circular polarizing plate described in 6 above, the polarizing element described in any one of 7 to 9 above, or the linear polarizing element described in any of 10 to 16 above. A lighting device, comprising:
[0042]
18. 18. A liquid crystal display device comprising a liquid crystal cell on the light emission side of the illumination device according to the above item 17.
[0043]
19. 19. The viewing angle widening liquid crystal display device according to the above item 18, wherein a viewing angle widening film for diffusing light rays on the viewing side transmitted through the liquid crystal cell is arranged on the viewing side with respect to the liquid crystal cell.
[0044]
20. 20. The viewing angle widening liquid crystal display device according to the above item 19, wherein a diffusion plate having substantially no back scattering and no depolarization is used as the viewing angle widening film.
[0045]
(Action)
As described above, in the present invention, in order to broaden the reflection band, the ultraviolet irradiation in the step (1) of performing ultraviolet irradiation from the alignment substrate side in a state where the liquid crystal mixture is in contact with the gas containing oxygen is performed a plurality of times. In each pulse irradiation, different conditions are used as the illuminance and irradiation temperature of the ultraviolet irradiation. As a result, more precise control of the reaction behavior of the polymerizable liquid crystal mixture can be realized, and a broadband cholesteric liquid crystal film can be obtained with a higher production rate than before.
[0046]
That is, in the ultraviolet irradiation condition of the step (1), the ultraviolet irradiation intensity is reduced and the ultraviolet irradiation time is lengthened as the number of times increases. The amount of radicals generated by the UV reaction of the photoreaction initiator in the liquid crystal composition per unit time is greatly changed between the first UV irradiation and the second UV irradiation due to the difference in irradiation intensity. In the first UV irradiation, a large amount of radicals are instantaneously formed under monomer-rich conditions at the beginning of the reaction, and a large gradient in the thickness direction is formed in the distribution of radicals due to oxygen inhibition and absorption of the liquid crystal composition. Thereby, a polymer / oligomer having an average molecular weight of about 10,000 to 500,000 is formed, and a concentration distribution is formed in the thickness direction. At this time, the polymerization ratio differs in the thickness direction because the reaction rates of the polymerizable mesogen compound (A) and the polymerizable chiral agent (B) in the liquid crystal composition are different. For this reason, the surface rich in the polymerizable chiral agent (B) has a short cholesteric pitch, and the surface in the opposite direction becomes long. Thereby, a cholesteric liquid crystal film having a broadband reflection wavelength as a whole is obtained.
[0047]
The broadband cholesteric liquid crystal film obtained in this manner functions as a broadband circularly polarized light reflector, has optically equivalent properties to Patent Documents 1 to 4, and the like, and has a larger number of laminated layers than the conventional manufacturing method. By reducing the thickness, the thickness can be reduced, and furthermore, it can be easily manufactured in a short time, and the cost can be reduced by improving the production speed.
[0048]
The broadband cholesteric liquid crystal film obtained by the production method of the present invention has a wide reflection bandwidth of a selective reflection wavelength of 200 nm or more, and has a wide reflection band. The reflection bandwidth is preferably 300 nm or more, more preferably 400 nm or more, and further preferably 450 nm. The reflection bandwidth of 200 nm or more is preferably provided in a visible light region, particularly in a wavelength region of 400 to 900 nm.
[0049]
It is an important problem that the circularly polarizing reflector has a reflection band of a wide band even in a long wavelength region in order to obtain good viewing angle characteristics of the liquid crystal display device. The long wavelength end of the selective reflection needs to reach 800 to 900 nm so that the transmitted light is not colored in a practical viewing angle range. According to the production method of the present invention, a broadband cholesteric liquid crystal film having a reflection band even in such a long wavelength region can be obtained. Such a broadband cholesteric liquid crystal film is not only used simply as a reflective polarizer for obtaining high luminance, but also in the case of a polarizing element created in combination with another optical element such as a retardation plate, similarly, oblique incidence other than the front. Stable optical characteristics for light rays are required.
[0050]
BEST MODE FOR CARRYING OUT THE INVENTION
The broadband cholesteric liquid crystal film of the present invention is obtained by ultraviolet polymerization of a liquid crystal mixture containing a polymerizable mesogen compound (A) and a polymerizable chiral agent (B).
[0051]
As the polymerizable mesogen compound (A), a compound having at least one polymerizable functional group and having a mesogen group composed of a cyclic unit or the like is preferably used. Examples of the polymerizable functional group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl ether group. Of these, an acryloyl group and a methacryloyl group are preferable. In addition, by using a compound having two or more polymerizable functional groups, a crosslinked structure can be introduced to improve the durability. Examples of the cyclic unit to be a mesogen group include biphenyl, phenylbenzoate, phenylcyclohexane, azoxybenzene, azomethine, azobenzene, phenylpyrimidine, diphenylacetylene, diphenylbenzoate, bicyclohexane, and the like. And cyclohexylbenzenes, terphenyls and the like. In addition, the terminal of these cyclic units may have a substituent such as a cyano group, an alkyl group, an alkoxy group, and a halogen group. The mesogen group may be bonded via a spacer that imparts flexibility. Examples of the spacer portion include a polymethylene chain and a polyoxymethylene chain. The number of repeating structural units forming the spacer portion is appropriately determined depending on the chemical structure of the mesogen portion, but the number of repeating units of the polymethylene chain is 0 to 20, preferably 2 to 12, and the number of repeating units of the polyoxymethylene chain is 0 to 10. 10, preferably 1-3.
[0052]
The molar extinction coefficient of the polymerizable mesogen compound (A) is 50 to 500 dm.³  mol^-1cm^-1Preferably, it is 365 nm. Those having the molar extinction coefficient have an ultraviolet absorbing ability. Molar extinction coefficient is 100-250 dm³  mol^-1cm^-1＠ 365 nm is more preferred. Molar extinction coefficient is 50 dm³  mol^-1cm^-1If it is smaller than 365 nm, there is no sufficient difference in polymerization rate, and it is difficult to broaden the band. On the other hand, 500dm³  mol^-1cm^-1If it is larger than 365 nm, the polymerization may not proceed completely and the curing may not be completed. The molar extinction coefficient is a value obtained by measuring a spectrophotometric spectrum of each material and measuring the obtained absorbance at 365 nm.
[0053]
The polymerizable mesogen compound (A) having one polymerizable functional group is, for example, represented by the following general formula:
Embedded image

(However, R₁  Represents a hydrogen atom or a methyl group. n represents an integer of 1 to 5. )).
[0054]
Specific examples of the polymerizable mesogen compound (A) having one polymerizable functional group include, for example,
Embedded image

The compound represented by is mentioned.
[0055]
Examples of the polymerizable chiral agent (B) include LC756 manufactured by BASF.
[0056]
The amount of the polymerizable chiral agent (B) is preferably about 1 to 20 parts by weight, and more preferably 3 to 7 parts by weight, based on 100 parts by weight of the total of the polymerizable mesogen compound (A) and the polymerizable chiral agent (B). Parts are more preferred. The helical torsional force (HTP) is controlled by the ratio of the polymerizable mesogen compound (A) and the polymerizable chiral agent (B). By setting the ratio within the above range, the reflection band can be selected so that the reflection spectrum of the obtained cholesteric liquid crystal film can cover a long wavelength region.
[0057]
The liquid crystal mixture usually contains a photopolymerization initiator (C). Various photopolymerization initiators (C) can be used without particular limitation. For example, Irgacure 184, Irgacure 907, Irgacure 369, Irgacure 651 and the like manufactured by Ciba Specialty Chemicals Inc. may be mentioned. The amount of the photopolymerization initiator is preferably about 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, based on 100 parts by weight of the total of the polymerizable mesogen compound (A) and the polymerizable chiral agent (B). Parts are more preferred.
[0058]
In order to widen the bandwidth of the resulting cholesteric liquid crystal film, the mixture may be mixed with an ultraviolet absorber to increase the difference in ultraviolet exposure intensity in the thickness direction. The same effect can be obtained by using a photoreaction initiator having a large molar extinction coefficient.
[0059]
The mixture can be used as a solution. Solvents used in preparing the solution, usually, chloroform, dichloromethane, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, halogenated hydrocarbons such as chlorobenzene, phenol, phenols such as parachlorophenol, benzene, toluene, Aromatic hydrocarbons such as xylene, methoxybenzene, 1,2-dimethoxybenzene, etc., acetone, methyl ethyl ketone, ethyl acetate, tert-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene bricol monomethyl ether, diethylene glycol Dimethyl ether, ethyl cellosolve, butyl cellosolve, 2-pyrrolidone, N-methyl-2-pyrrolidone, pyridine, triethylamine, Rahidorofuran, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, can be used acetonitrile, butyronitrile, carbon disulfide, cyclopentanone, cyclohexanone and the like. The solvent to be used is not particularly limited, but methyl ethyl ketone, cyclohexanone, cyclopentanone and the like are preferable. Since the concentration of the solution depends on the solubility of the thermotropic liquid crystalline compound and the final thickness of the target cholesteric liquid crystal film, it cannot be specified unconditionally, but is usually preferably about 3 to 50% by weight.
[0060]
The production of the broadband cholesteric liquid crystal film of the present invention includes a step of applying the liquid crystal mixture to an alignment substrate, and a step of irradiating the liquid crystal mixture with ultraviolet rays and polymerizing and curing.
[0061]
As the alignment base material, a conventionally known one can be used. For example, a thin film made of polyimide, polyvinyl alcohol, etc. is formed on a substrate and then rubbed with a rayon cloth or the like. A rubbing film, an oblique deposition film, a polymer having a photocrosslinking group such as cinnamate or azobenzene, or a polarized ultraviolet light A photo-alignment film, a stretched film, or the like irradiated with is used. In addition, the orientation can be performed by a magnetic field, an electric field orientation, and a shear stress operation.
[0062]
The type of the base material is not particularly limited, but a material having a high transmittance is desirable in view of the method of irradiating irradiation light (ultraviolet rays) from the base material side. For example, the base material is required to have a transmittance of 10% or more, preferably 20% or more in an ultraviolet region of 200 nm or more and 400 nm or less, more preferably 300 nm or more and 400 nm or less. Specifically, a plastic film having a transmittance of 10% or more, more preferably 20% or more, for ultraviolet light having a wavelength of 365 nm is preferable. The transmittance is a value measured by U-4100 Spectrophotometer manufactured by HITACHI.
[0063]
As the substrate, a film or a glass plate made of a plastic such as polyethylene terephthalate, triacetyl cellulose, norbornene resin, polyvinyl alcohol, polyimide, polyarylate, polycarbonate, polysulfone or polyethersulfone is used. For example, Triacetylcellulose manufactured by Fudo Photo Film Co., Ltd., ARTON manufactured by JSR, Zeonex manufactured by Zeon Corporation, and the like can be used.
[0064]
Further, polymer films described in JP-A-2001-343529 (WO 01/37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a thermoplastic resin having a side chain And / or an unsubstituted phenyl and a resin composition containing a thermoplastic resin having a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film composed of a mixed extruded product of a resin composition or the like can be used.
[0065]
The substrate may be used while being bonded to the cholesteric liquid crystal layer, or may be peeled off. In the case of being used while being bonded, a material having a sufficiently small retardation value for practical use is used.
[0066]
When the substrate is used with the substrate adhered, it is desirable that the substrate does not decompose, deteriorate or yellow even when irradiated with ultraviolet rays. For example, the desired purpose of blending a light stabilizer or the like in the above-described base material can be achieved. As the light stabilizer, Tinuvin 120, 144, etc. manufactured by Ciba Specialty Chemicals Co., Ltd. are preferably used. If the wavelength of 300 nm or less is cut from the exposure light, coloring, deterioration and yellowing can be reduced.
[0067]
The coating thickness of the liquid crystal mixture (the coating thickness after drying the solvent in the case of a solution) is preferably about 1 to 20 μm. When the coating thickness is less than 1 μm, the reflection bandwidth can be ensured, but the degree of polarization itself tends to decrease, which is not preferable. The coating thickness is preferably 2 μm or more, more preferably 3 μm or more. On the other hand, when the coating thickness is larger than 20 μm, no remarkable improvement is observed in both the reflection bandwidth and the degree of polarization, and the cost is simply increased, which is not preferable. The coating thickness is preferably 15 μm or less, more preferably 10 μm or less.
[0068]
As a method of applying the mixed solution to the alignment substrate, for example, a roll coating method, a gravure coating method, a spin coating method, a bar coating method, or the like can be adopted. After the application of the mixed solution, the solvent is removed, and a liquid crystal layer is formed on the substrate. The conditions for removing the solvent are not particularly limited, and it is sufficient that the solvent can be substantially removed and the liquid crystal layer does not flow or does not flow down. Usually, the solvent is removed by using drying at room temperature, drying in a drying furnace, heating on a hot plate, or the like.
[0069]
Next, the liquid crystal layer formed on the alignment base material is brought into a liquid crystal state, and cholesteric alignment is performed. For example, heat treatment is performed so that the liquid crystal layer has a liquid crystal temperature range. The heat treatment can be performed by the same method as the above-described drying method. The heat treatment temperature varies depending on the type of the liquid crystal material and the alignment base material, and cannot be unconditionally determined. However, the heat treatment temperature is usually in the range of 60 to 300 ° C, preferably 70 to 200 ° C. Further, the heat treatment time cannot be specified unconditionally because it differs depending on the heat treatment temperature and the type of liquid crystal material or alignment substrate to be used, but is usually selected in the range of 10 seconds to 2 hours, preferably 20 seconds to 30 minutes.
[0070]
The step of applying to the alignment base material and irradiating the liquid crystal mixture with ultraviolet rays includes the above steps (1) and (2).
[0071]
In the step (1), in a state where the liquid crystal mixture is in contact with a gas containing oxygen, at a temperature of 20 ° C. or more, 1 to 200 mW / cm²  UV irradiation intensity, in the range of 0.2 to 30 seconds, every time the number of times increases, the UV irradiation intensity is low, and while increasing the UV irradiation time, UV irradiation from the alignment substrate side three times or more Irradiate.
[0072]
Thereby, the liquid crystal mixture is polymerized to form a polymer / oligomer having an average molecular weight of about 10,000 to 500,000, and a difference in reaction rate due to oxygen inhibition in the thickness direction between the alignment substrate side and the opposite side (oxygen interface side). In addition, a difference in the amount of generated radicals due to the absorption of ultraviolet light in the liquid crystal composition occurs, and a layer in which the amount of generated polymer / oligomer is continuously distributed in the thickness direction is formed. At the same time, the pitch is continuously changed by making the concentration gradient of the unpolymerized monomer component uniform.
[0073]
As described above, in step (1), in order to broaden the band, in pulse irradiation of ultraviolet irradiation, different conditions are used for the illuminance and irradiation time of exposure. This utilizes the fact that the effective depth of polymerization inhibition due to oxygen penetrating from the air interface side varies depending on the illuminance of exposure.
[0074]
In step (1), the temperature at the time of ultraviolet irradiation is set to 20 ° C. or higher in order to polymerize and cure the liquid crystal mixture in a favorable alignment state. On the other hand, the upper limit of the temperature is not particularly limited, but is preferably 120 ° C. or lower. If the temperature is higher than 120 ° C., diffusion may occur during irradiation, which may make management difficult. From these points, the temperature is preferably from 20C to 80C.
[0075]
UV irradiation intensity is 1 to 200 mW / cm²  And 4 to 100 mW / cm²  Is preferred. UV irradiation intensity is 1mW / cm²  If the molecular weight is lower, polymerization is not performed so that a monomer distribution is formed in the thickness direction, so that the band is not broadened. UV irradiation intensity is 200 mW / cm²  If it is higher, the polymerization reaction rate becomes larger than the diffusion rate, and the band is not broadened.
[0076]
The time of one ultraviolet irradiation of the pulse irradiation in the step (1) is adjusted within a range of 0.2 to 30 seconds. UV irradiation time depends on illuminance. Each time the number of times of pulse irradiation increases, the irradiation is performed while lowering the UV irradiation intensity and extending the UV irradiation time. The number of times of pulse irradiation is 3 or more times, preferably 3 to 6 times, and more preferably 4 to 5 times.
[0077]
Specifically, the UV illuminance is 30 to 200 mW / cm²  , Preferably 30 to 100 mW / cm²  Is preferably 0.2 to 5 seconds, more preferably 0.5 to 2 seconds. When the time is shorter than 0.2 seconds, the polymerization is not performed so that the monomer distribution is formed in the thickness direction, so that there is a tendency that the band is not broadened. If the time is longer than 5 seconds, the change in the pitch of the cholesteric layer is not a continuous change from large to small from the substrate side to the air interface side, but is a discontinuous change. If the pitch changes discontinuously, coloring when viewed obliquely becomes severe. UV irradiance is 15-30mW / cm²  , The ultraviolet irradiation time is preferably from 3 to 20 seconds, more preferably from 5 to 15 seconds. When the time is shorter than 3 seconds, the polymerization is not performed so that the monomer distribution is formed in the thickness direction, so that there is a tendency that the band is not broadened. On the other hand, if the time is longer than 15 seconds, the polymerization time becomes longer and the process becomes disadvantageous, which is not preferable. UV illuminance is 1 to 15mW / cm²  , The ultraviolet irradiation time is preferably from 10 to 30 seconds, more preferably from 10 to 20 seconds. When the time is shorter than 10 seconds, the polymerization is not carried out to such an extent that the monomer distribution is formed in the thickness direction. If it is longer than 30 seconds. It is not preferable because the polymerization time becomes longer and the process becomes disadvantageous.
[0078]
The exposure environment for ultraviolet irradiation is performed in a state where the liquid crystal mixture applied to the alignment base material is in contact with a gas containing oxygen. It is preferable that the gas containing oxygen contains 0.5% or more of oxygen. Such an environment may be any environment that can utilize oxygen polymerization inhibition, and can be performed under a general atmospheric atmosphere. The oxygen concentration may be increased or decreased in consideration of the wavelength width for controlling the pitch in the thickness direction and the speed required for polymerization. Note that the required amount of the photopolymerization initiator (C) tends to increase under an air atmosphere. The desired purpose can be achieved with an addition amount of about 1 to 5 parts by weight based on 100 parts by weight of the total of the chiral agent (B).
[0079]
In the above-mentioned ultraviolet irradiation, if the weight average molecular weight of the formed polymer / oligomer is too small, the diffusion rate becomes too high. Care should therefore be taken to ensure that the uncontrolled diffusion rate does not even out the polymer / oligomer concentration gradient. It is necessary not only to form a large change in the cholesteric pitch length in the thickness direction of the liquid crystal layer but also to maintain this. If the polymer / oligomer is too low in molecular weight, the formed gradient cannot be maintained, and the structure is lost due to molecular diffusion. In order to satisfy the conditions for controlling the diffusion rate under industrial conditions, a polymer / oligomer is formed in a weight average molecular weight range of about 10,000 to 500,000. The weight average molecular weight of the polymer / oligomer is preferably from 100,000 to 300,000. The weight average molecular weight of the polymer / oligomer is a value measured by the GPC method. The weight average molecular weight was calculated using polyethylene oxide as a standard sample. Main unit: Tosoh HLC-8120GPC, column: Tosoh SuperAWM-H + SuperAWM-H + SuperAW3000 (each 6 mmφ × 15 cm, total 45 cm), column temperature: 40 ° C., eluent: 10 mM-LiBr / NMP, flow rate: 0.4 ml / min, inlet pressure: 8.5 MPa, sample concentration: 0.1% NMP solution, detector: differential refractometer (RI).
[0080]
In the step (1), each time the number of times of pulse irradiation increases, the effective depth of polymerization inhibition due to oxygen penetrating from the oxygen interface side can be further increased, and the polymer / oligomer is formed with a concentration gradient in the thickness direction. Due to this, the concentration gradient of the unpolymerized monomer component formed conversely can be made uniform. At the same time, by allowing the reaction to proceed only in the long pitch region on the alignment substrate side, it is possible to further increase the pitch on the alignment substrate side.
[0081]
In Patent Literature 2, the temperature conditions for the first ultraviolet irradiation and the second ultraviolet irradiation are changed, and the time required for the composition ratio to change in the thickness direction is separately provided in a dark place. However, in order to cover substantially the entire visible light region by this method, it is necessary to wait about 120 minutes for mass transfer due to the temperature change. On the other hand, the manufacturing method of the present invention does not require a dark place. Further, since the process can be completed in a short time within one minute, a practical high-efficiency production rate can be produced.
[0082]
As described above, the bandwidth can be widened by the step (1) as described in the following embodiment, and the viewing angle at which the coloring and omission due to the blue shift of the obliquely incident light becomes extremely large, and the coloring due to the viewing angle is extremely large. It can be reduced.
[0083]
Next, in step (2), ultraviolet irradiation is performed in the absence of oxygen. By such ultraviolet irradiation, the cholesteric reflection band expanded in the step (1) is cured without deteriorating. Thereby, the pitch change structure is fixed without deteriorating.
The absence of oxygen can be, for example, an inert gas atmosphere. The inert gas is not particularly limited as long as it does not affect the ultraviolet polymerization of the liquid crystal mixture. Examples of such an inert gas include nitrogen, argon, helium, neon, xenon, and krypton. Of these, nitrogen is the most versatile and preferred. In addition, by bonding a transparent base material to the cholesteric liquid crystal layer, it can be made in the absence of oxygen.
[0084]
In the step (2), the ultraviolet irradiation may be performed from either the alignment substrate side or the applied liquid crystal mixture side.
[0085]
The ultraviolet irradiation condition is not particularly limited as long as the liquid crystal mixture is cured. Normally, 40 to 300 mW / cm²  It is preferable to irradiate at an irradiation intensity of about 1 to 60 seconds. The irradiation temperature is about 20 to 100 ° C.
[0086]
As a result, the reliability is remarkably improved due to an increase in the crosslink density and an increase in the molecular weight of the liquid crystal layer. In the present invention, ultraviolet irradiation is performed from the alignment substrate surface side in order to positively utilize oxygen inhibition in the first ultraviolet irradiation in step (1) and the second ultraviolet irradiation in step (2). For this reason, it is possible to form a large gradient in the reaction rate in the thickness direction.However, problems such as insufficient hardness and strength of the film surface due to low polymerization rate on the air interface side or insufficient long-term reliability Problems may occur. For this reason, in the step (2), the third ultraviolet irradiation is performed in an oxygen-free atmosphere to complete the polymerization of the remaining monomer and enhance the film quality. In this case, under an air atmosphere (in the presence of oxygen), the reaction rate on the surface is not sufficiently improved, and it is difficult for the reaction rate to exceed 90%. Therefore, in order to obtain sufficient reliability, it is desired to perform ultraviolet irradiation in the absence of oxygen. The direction of the irradiation surface is not particularly limited. This is because irradiation from the liquid crystal layer side is desirable, but the reaction on the surface sufficiently proceeds even under irradiation from the substrate side in a nitrogen atmosphere.
[0087]
The cholesteric liquid crystal film thus obtained is used without being separated from the substrate, or may be used after being separated from the substrate.
[0088]
The broadband cholesteric liquid crystal film of the present invention is used as a circularly polarizing plate. A λ / 4 plate can be laminated on the circularly polarizing plate to form a linearly polarizing element. The cholesteric liquid crystal film, which is a circularly polarizing plate, is preferably laminated on the λ / 4 plate so that the pitch length is continuously narrowed.
[0089]
The λ / 4 plate is not particularly limited, but may be a general-purpose transparent resin film such as polycarbonate, polyethylene terephthalate, polystyrene, polysulfone, polyvinyl alcohol, polymethyl methacrylate or the like, which generates a phase difference by stretching, or a JSR ARTON film. A suitable norbornene-based resin film is preferably used. Further, it is preferable to perform biaxial stretching and use a retardation plate that compensates for a change in retardation value due to the incident angle, since the viewing angle characteristics can be improved. Alternatively, a λ / 4 plate obtained by fixing a λ / 4 layer obtained by aligning liquid crystal other than the expression of a retardation by stretching a resin may be used. In this case, the thickness of the λ / 4 plate can be significantly reduced. The thickness of the λ / 4 wavelength plate is usually preferably from 0.5 to 200 μm, and particularly preferably from 1 to 100 μm.
[0090]
A retardation plate that functions as a λ / 4 wavelength plate in a wide wavelength range such as a visible light region shows, for example, a retardation layer that functions as a λ / 4 wavelength plate with respect to light-color light having a wavelength of 550 nm and other retardation characteristics. It can be obtained by a method of superimposing a retardation layer, for example, a retardation layer functioning as a λ / 2 wavelength plate. Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement film may be composed of one or more retardation layers.
[0091]
An absorptive polarizer is attached to the transmission axis of the linear polarizing element so that its transmission axis direction is aligned.
[0092]
The polarizer is not particularly limited, and various types can be used. Examples of the polarizer include a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymer-based partially saponified film, and a dichromatic dye such as iodine or a dichroic dye. And uniaxially stretched by adsorbing a hydrophilic substance, or a polyene-based oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride. Among these, a polarizer composed of a polyvinyl alcohol-based film and a dichroic substance such as iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.
[0093]
A polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine and uniaxially stretching can be produced, for example, by dyeing polyvinyl alcohol by immersing it in an aqueous solution of iodine, and stretching the film to 3 to 7 times its original length. If necessary, it can be immersed in an aqueous solution of boric acid or potassium iodide. Further, if necessary, the polyvinyl alcohol-based film may be immersed in water and washed with water before dyeing. By washing the polyvinyl alcohol-based film with water, dirt on the surface of the polyvinyl alcohol-based film and an anti-blocking agent can be washed, and by swelling the polyvinyl alcohol-based film, the effect of preventing unevenness such as uneven dyeing can be obtained. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. Stretching can be performed in an aqueous solution of boric acid or potassium iodide or in a water bath.
[0094]
The polarizer is usually provided with a transparent protective film on one or both sides and used as a polarizing plate. The transparent protective film preferably has excellent transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like. Examples of the transparent protective film include films made of transparent polymers such as polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polycarbonate polymers, and acrylic polymers such as polymethyl methacrylate. Is raised. Styrene polymers such as polystyrene and acrylonitrile / styrene copolymer; polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure; olefin polymers such as ethylene / propylene copolymer; vinyl chloride polymers; nylon and aromatic polyamides And a film made of a transparent polymer such as an amide-based polymer. Furthermore, imide-based polymers, sulfone-based polymers, polyethersulfone-based polymers, polyetheretherketone-based polymers, polyphenylene sulfide-based polymers, vinyl alcohol-based polymers, vinylidene chloride-based polymers, vinylbutyral-based polymers, arylate-based polymers, and polyoxymethylene-based polymers Films made of transparent polymers such as polymers, epoxy polymers and blends of the above polymers are also included. Particularly, those having low optical birefringence are preferably used. From the viewpoint of a protective film for a polarizing plate, triacetyl cellulose, polycarbonate, an acrylic polymer, a cycloolefin resin, a polyolefin having a norbornene structure, and the like are preferable.
[0095]
Further, polymer films described in JP-A-2001-343529 (WO 01/37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a thermoplastic resin having a side chain And / or an unsubstituted phenyl and a resin composition containing a thermoplastic resin having a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film composed of a mixed extruded product of a resin composition or the like can be used.
[0096]
A transparent substrate that can be particularly preferably used in view of polarization characteristics and durability is a triacetyl cellulose film whose surface has been saponified with an alkali or the like. Although the thickness of the transparent protective film can be determined as appropriate, it is generally about 10 to 500 μm from the viewpoint of workability such as strength and handleability, and thin layer property. In particular, 20 to 300 μm is preferable, and 30 to 200 μm is more preferable.
[0097]
Further, it is preferable that the transparent protective film has as little coloring as possible. Therefore, Rth = [(nx + ny) / 2−nz] · d (where nx and ny are the main refractive indices in the film plane, nz is the refractive index in the film thickness direction, and d is the film thickness). A protective film having a retardation value in the film thickness direction of -90 nm to +75 nm is preferably used. By using a film having a retardation value (Rth) in the thickness direction of -90 nm to +75 nm, coloring (optical coloring) of the polarizing plate caused by the protective film can be substantially eliminated. The thickness direction retardation value (Rth) is more preferably -80 nm to +60 nm, and particularly preferably -70 nm to +45 nm.
[0098]
As the transparent protective film, a transparent protective film made of the same polymer material on both sides may be used, or a transparent protective film made of a different polymer material or the like may be used.
[0099]
The surface of the transparent protective film on which the polarizer is not adhered may be subjected to a hard coat layer, an antireflection treatment, a treatment for preventing sticking, and a treatment for diffusion or antiglare.
[0100]
The hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate, for example, by applying a suitable ultraviolet-curable resin such as an acrylic resin or a silicone resin to a cured film having excellent hardness and sliding properties, etc., as a transparent protective film. It can be formed by a method of adding to the surface of. The anti-reflection treatment is performed for the purpose of preventing the reflection of external light on the polarizing plate surface, and can be achieved by forming an anti-reflection film or the like according to the related art. In addition, the anti-sticking treatment is performed for the purpose of preventing adhesion to an adjacent layer.
[0101]
The anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the visibility of the light transmitted through the polarizing plate. The transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a method of mixing transparent fine particles or the like. As the fine particles to be contained in the formation of the surface fine uneven structure, for example, a conductive material composed of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide and the like having an average particle size of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles that may be used and organic fine particles made of a crosslinked or uncrosslinked polymer or the like are used. When forming the fine surface unevenness structure, the amount of the fine particles to be used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, per 100 parts by weight of the transparent resin forming the fine surface unevenness structure. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle expanding function) for diffusing light transmitted through the polarizing plate to increase the viewing angle or the like.
[0102]
The anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer and the like can be provided on the transparent protective film itself, or can be provided as an optical layer separately from the transparent protective layer.
[0103]
The above-described linear polarizing element may be provided with an adhesive layer for bonding to another member such as a liquid crystal cell. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited, and for example, an acrylic polymer, a silicone-based polymer, a polyester, a polyurethane, a polyamide, a polyether, and a polymer having a fluorine-based or rubber-based polymer as a base polymer are appropriately selected. Can be used. In particular, an acrylic adhesive having excellent optical transparency, exhibiting appropriate wettability, cohesiveness and adhesive adhesive properties and having excellent weather resistance and heat resistance can be preferably used.
[0104]
In addition to the above, prevention of foaming and peeling phenomena due to moisture absorption, reduction of optical characteristics due to thermal expansion difference and the like, prevention of warpage of the liquid crystal cell, and, in view of the formability of a liquid crystal display device having high quality and excellent durability, etc. An adhesive layer having low moisture absorption and excellent heat resistance is preferred.
[0105]
The adhesive layer is, for example, a natural or synthetic resin, in particular, a tackifier resin, or a filler, a pigment, a colorant, an antioxidant, or the like made of glass fiber, glass beads, metal powder, other inorganic powder, and the like. May be added to the pressure-sensitive adhesive layer. In addition, an adhesive layer containing fine particles and exhibiting light diffusibility may be used.
[0106]
The attachment of the adhesive layer can be performed by an appropriate method. As an example thereof, for example, an adhesive solution of about 10 to 40% by weight is prepared by dissolving or dispersing a base polymer or a composition thereof in a solvent composed of a single solvent or a mixture of appropriate solvents such as toluene and ethyl acetate, A method in which it is directly attached on the polarizer by an appropriate developing method such as a casting method or a coating method, or a method in which an adhesive layer is formed on a separator according to the above and transferred to an optical element. Is raised. The pressure-sensitive adhesive layer can be provided as a superposed layer of different compositions or types of layers. The thickness of the pressure-sensitive adhesive layer can be appropriately determined depending on the purpose of use, adhesive strength, and the like, and is generally 1 to 500 µm, preferably 5 to 200 µm, particularly preferably 10 to 100 µm.
[0107]
A separator is temporarily attached to the exposed surface of the adhesive layer for the purpose of preventing contamination and the like until the adhesive layer is put to practical use and covered. This can prevent the adhesive layer from coming into contact with the adhesive layer in a normal handling state. Except for the above thickness conditions, the separator may be, for example, a plastic film, a rubber sheet, paper, cloth, a nonwoven fabric, a net, a foamed sheet or a metal foil, a suitable thin sheet such as a laminate thereof, or a silicone-based material as necessary. Appropriate conventional ones, such as those coated with an appropriate release agent such as a long-chain alkyl-based, fluorine-based, or molybdenum sulfide, may be used.
[0108]
Each layer such as an adhesive layer may be subjected to ultraviolet absorption by a method such as a method of treating with an ultraviolet absorber such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. It may have a function.
[0109]
The linear polarizing element of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The formation of the liquid crystal display device can be performed according to a conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell and an optical element, and an illumination system as required, and incorporating a drive circuit, and uses the linear polarizing element of the present invention. There is no particular limitation except for the point, and it can be in accordance with the related art. As for the liquid crystal cell, any type such as TN type, STN type and π type can be used.
[0110]
Appropriate liquid crystal display devices such as a liquid crystal display device in which the linear polarizing element is arranged on one side or both sides of a liquid crystal cell, and an illumination system using a backlight or a reflector can be formed. In that case, the linear polarizing element according to the present invention can be installed on one side or both sides of the liquid crystal cell. When linear polarizing elements are provided on both sides, they may be the same or different. Further, when forming the liquid crystal display device, for example, a suitable component such as a diffusion plate, an anti-glare layer, an antireflection film, a protection plate, a prism array, a lens array sheet, a light diffusion plate, a backlight, etc. Two or more layers can be arranged.
[0111]
Further, a circularly polarizing plate (reflection polarizer) using the cholesteric liquid crystal film has a front phase difference (normal line) between at least two layers of reflection polarizers (a) in which the wavelength bands of selective reflection of polarized light overlap each other. Direction) is substantially zero, and is used in a polarizing element system in which a retardation layer (b) having a phase difference of λ / 8 or more with respect to incident light incident at an angle of 30 ° or more with respect to the normal direction is arranged. In addition, the cholesteric liquid crystal film may have either the maximum pitch or the minimum pitch of the spiral twisted molecular structure on the side of the retardation layer (b), but from the viewpoint of viewing angle (good viewing angle, small coloring). If the reflection polarizer (a) is expressed as (maximum pitch / minimum pitch), it is preferable to arrange the reflection polarizer in the following order: maximum pitch / minimum pitch / phase difference layer (b) / maximum pitch / minimum pitch. When a λ / 4 plate is combined, it is preferable to arrange the reflective polarizer (a) such that the minimum pitch side is the λ / 4 plate side.
[0112]
The polarizing element system, that is, the cholesteric liquid crystal laminate having a broadband selective reflection function has a circularly polarized light reflection / transmission function in the front direction, and can be used as a broadband circularly polarizing plate in a liquid crystal display device. In this case, it can be used as a circularly polarizing plate by arranging it on the light source side of a circularly polarized mode liquid crystal cell, for example, a transmissive VA mode liquid crystal cell having a multi-domain.
[0113]
The phase difference layer (b) has a phase difference of almost zero in the front direction, and has a phase difference of λ / 8 or more with respect to incident light at an angle of 30 ° from the normal direction. The front phase difference is desirably λ / 10 or less because the purpose is to maintain polarized light that is vertically incident.
[0114]
The incident light from an oblique direction is appropriately determined by the angle of total reflection so as to be efficiently polarized and converted. For example, in order to achieve total reflection at an angle of about 60 ° from the normal, the phase difference measured at 60 ° may be determined so as to be about λ / 2. However, the transmitted light by the reflective polarizer (a) changes its polarization state also due to the birefringence of the reflective polarizer itself as a C plate. The phase difference may be a value smaller than λ / 2. Since the phase difference of the C plate monotonically increases as the incident light is inclined, an effective total reflection is caused when the incident light is inclined at an angle of 30 ° or more. You only have to.
[0115]
The material of the retardation layer (b) is not particularly limited as long as it has the above optical characteristics. For example, a cholesteric liquid crystal having a selective reflection wavelength other than the visible light region (380 nm to 780 nm) in which the planar alignment state is fixed, a rod-like liquid crystal in which the homeotropic alignment state is fixed, a discotic liquid crystal columnar alignment or a nematic alignment. And a biaxially oriented polymer film in which a negative uniaxial crystal is oriented in a plane.
[0116]
In the present invention, the C plate in which the planar alignment state of the cholesteric liquid crystal having a selective reflection wavelength other than the visible light region (380 nm to 780 nm) is fixed, the cholesteric liquid crystal has no selective reflection wavelength in the visible light region. Is desirable. Therefore, it is necessary that the selective reflection light is not in the visible region. The selective reflection is uniquely determined by the cholesteric chiral pitch and the refractive index of the liquid crystal. The value of the center wavelength of the selective reflection may be in the near-infrared region, but it is more preferably in the ultraviolet region of 350 nm or less because it is affected by optical rotation and a somewhat complicated phenomenon occurs. The formation of the cholesteric liquid crystal layer is performed in the same manner as the formation of the cholesteric layer in the reflective polarizer described above.
[0117]
In the present invention, the C plate in which the homeotropic alignment state is fixed, a liquid crystalline thermoplastic resin or a liquid crystal monomer exhibiting nematic liquid crystallinity at a high temperature and an alignment aid as necessary are irradiated with ionizing radiation such as an electron beam or ultraviolet light. A polymerizable liquid crystal polymerized by heat or a mixture thereof is used. The liquid crystal properties may be either lyotropic or thermotropic. However, from the viewpoint of easy control and easy formation of a monodomain, it is desirable that the liquid crystal be a thermotropic liquid crystal. The homeotropic alignment can be obtained, for example, by applying the birefringent material on a film on which a vertical alignment film (such as a long-chain alkylsilane) is formed, and developing and fixing a liquid crystal state.
[0118]
As a C-plate using discotic liquid crystal, a discotic liquid crystal material having a negative uniaxial property such as a phthalocyanine or triphenylene compound having a molecular spread in a plane as a liquid crystal material is used as a nematic phase or a columnar phase. It is expressed and fixed. The negative uniaxial inorganic layered compound is described in detail in, for example, JP-A-6-82777.
[0119]
A C-plate utilizing biaxial orientation of a polymer film is a method of biaxially stretching a polymer film having a positive refractive index anisotropy in a well-balanced manner, a method of pressing a thermoplastic resin, and a method of cutting a parallel-oriented crystal. It can be obtained by a method or the like.
[0120]
Lamination of each layer may be performed only by stacking, but it is desirable to laminate each layer using an adhesive or a pressure-sensitive adhesive from the viewpoint of workability and light use efficiency. In this case, the adhesive or the pressure-sensitive adhesive is preferably transparent, has no absorption in the visible light range, and has a refractive index as close as possible to the refractive index of each layer from the viewpoint of suppressing surface reflection. From this viewpoint, for example, an acrylic pressure-sensitive adhesive can be preferably used. Each layer separately forms a monodomain in the form of an alignment film, and is sequentially laminated on a light-transmissive substrate by a method such as transfer, or without an adhesive layer or the like. Can be formed as appropriate, and each layer can be directly formed sequentially.
[0121]
Particles may be added to each layer and (adhesive) adhesive layer to adjust the degree of diffusion, if necessary, to impart isotropic scattering, an ultraviolet absorber, an antioxidant, and leveling during film formation. A surfactant or the like can be appropriately added for the purpose of imparting properties.
[0122]
The polarizing element (cholesteric liquid crystal laminate) of the present invention has a function of reflecting / transmitting circularly polarized light. By combining this with a λ / 4 plate, it can be used as a linearly polarizing element that converts transmitted light into linearly polarized light. Examples of the λ / 4 plate include those similar to the above.
[0123]
Although the λ / 4 plate functions well only for a specific wavelength with a single layer made of a single material, there is a problem that the function of the λ / 4 plate is reduced for other wavelengths due to wavelength dispersion characteristics. Therefore, if the λ / 2 plate and the λ / 2 plate are laminated while defining an axis angle, the λ / 2 plate can be used as a broadband λ / 4 plate that functions within a practically acceptable range over the entire visible light range. In this case, each of the λ / 4 plate and the λ / 2 plate may be the same material, or may be a combination of those made of different materials obtained by the same method as the λ / 4 plate described above.
[0124]
For example, a λ / 4 plate (140 nm) is laminated on a broadband circularly polarizing plate, and a λ / 2 plate (270 nm) is arranged at 17.5 degrees with respect to this axis angle. In this case, the transmission polarization axis is 10 degrees with respect to the axis of the λ / 4 plate. Since the bonding angle varies depending on the phase difference value of each retardation plate, the bonding angle is not limited to the above bonding angle.
[0125]
An absorptive polarizer is attached to the transmission axis of the linear polarizing element so that its transmission axis direction is aligned.
[0126]
(Arrangement of diffuse reflection plate)
It is desirable to dispose a diffuse reflection plate below the light guide plate as the light source (on the side opposite to the surface where the liquid crystal cells are disposed). The main component of the light beam reflected by the collimating film is an oblique incident component, which is specularly reflected by the collimating film and returned toward the backlight. Here, if the rear-side reflector has high specular reflectivity, the reflection angle is preserved, and the light cannot be emitted in the front direction, resulting in light loss. Therefore, it is desirable to dispose a diffuse reflector in order to increase the scattered reflection component in the front direction without preserving the reflection angle of the reflected return light beam.
[0127]
(Arrangement of diffusion plate)
It is also desirable to provide a suitable diffuser between the collimating film and the backlight source in the present invention. This is because the light reuse efficiency is increased by scattering the obliquely incident and reflected light rays in the vicinity of the backlight light guide and scattering a part of the light rays in the vertical incidence direction.
[0128]
The diffusion plate to be used can be obtained by a method of embedding fine particles having different refractive indices in a resin, in addition to a material having a surface irregular shape. This diffusion plate may be sandwiched between the collimating film and the backlight, or may be bonded to the collimating film.
[0129]
When the liquid crystal cell to which the collimating film is attached is arranged close to the backlight, Newton rings may be generated in the gap between the film surface and the backlight, but the light guide plate side surface of the collimating film in the present invention. By disposing a diffusion plate having surface irregularities on the surface, the generation of Newton rings can be suppressed. Further, a layer having both a concavo-convex structure and a light-diffusing structure may be formed on the surface of the collimating film in the present invention.
[0130]
(Arrangement of viewing angle expansion film)
The viewing angle expansion in the liquid crystal display device of the present invention, combined with a parallelized backlight, diffuses light beams having good display characteristics near the front obtained from the liquid crystal display device and is uniform within the entire viewing angle. It is obtained by obtaining good display characteristics.
[0131]
As the viewing angle widening film used here, a diffusion plate having substantially no back scattering is used. The diffusion plate can be provided as a diffusion adhesive. The arrangement location is on the viewing side of the liquid crystal display device, but it can be used on either side of the polarizing plate. However, in order to prevent the influence of pixel bleeding and the like and the decrease in contrast due to slightly remaining back scattering, it is desirable to provide the layer as close to the cell as possible, such as between the polarizing plate and the liquid crystal cell. In this case, a film that does not substantially eliminate polarized light is desirable. For example, a fine particle-dispersed diffusion plate as disclosed in JP-A-2000-347006 and JP-A-2000-347007 is preferably used.
[0132]
When the viewing angle widening film is positioned outside the polarizing plate, the parallelized light is transmitted from the liquid crystal layer to the polarizing plate. Therefore, in the case of a TN liquid crystal cell, the viewing angle compensating retardation plate need not be particularly used. In the case of an STN liquid crystal cell, it is only necessary to use a retardation film in which only the front characteristics are well compensated. In this case, since the viewing angle widening film has an air surface, it is possible to adopt a type using a refraction effect due to the surface shape.
[0133]
On the other hand, when a viewing angle widening film is inserted between the polarizing plate and the liquid crystal layer, the light is diffused at the stage of transmission through the polarizing plate. In the case of a TN liquid crystal, it is necessary to compensate for the viewing angle characteristics of the polarizer itself. In this case, it is necessary to insert a retardation plate for compensating the viewing angle characteristics of the polarizer between the polarizer and the viewing angle widening film. In the case of the STN liquid crystal, it is necessary to insert a retardation plate for compensating the viewing angle characteristics of the polarizer in addition to the front retardation compensation of the STN liquid crystal.
[0134]
In the case of a viewing angle widening film having a regular structure inside, such as a conventional microlens array film or hologram film, the microlens of a black matrix of a liquid crystal display device or a conventional parallel light conversion system of a backlight Moire was likely to occur due to interference with microstructures such as arrays / prism arrays / louvers / micromirror arrays. However, in the parallel light-converting film of the present invention, the regular structure is not visually recognized in the plane, and there is no regular modulation in the emitted light. Therefore, it is not necessary to consider the compatibility with the viewing angle widening film and the arrangement order. Therefore, the viewing angle widening film is not particularly limited as long as it does not cause interference / moire with the pixel black matrix of the liquid crystal display device, and the options are wide.
[0135]
In the present invention, a viewing angle widening film has substantially no back scattering, does not eliminate polarized light, and is a light scattering plate as described in JP-A-2000-347006 and JP-A-2000-347007. A haze of 80% to 90% is suitably used. In addition, even if it has a regular structure inside, such as a hologram sheet, a microprism array, a microlens array, etc., it can be used without forming interference / moire with the pixel black matrix of the liquid crystal display device.
[0136]
The liquid crystal display device is manufactured by appropriately using various optical layers and the like according to a conventional method.
[0137]
【Example】
Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
[0138]
Example 1
Photopolymerizable mesogen compound (polymerizable nematic liquid crystal monomer, compound (1) of the above formula 4, molar extinction coefficient: 220 dm³  mol^-1cm^-1@ 365 nm. ) 94.8 parts by weight and 5.2 parts by weight of a polymerizable chiral agent (LC756 manufactured by BASF) and a solvent (cyclopentanone) were adjusted and blended so that the central wavelength of selective reflection became 550 nm. Then, a coating liquid (solid content: 30% by weight) was prepared by adding 3% by weight of a photopolymerization initiator (Irgacure 907, manufactured by Ciba Specialty Chemicals). The coating liquid was applied on a stretched polyethylene terephthalate film (oriented substrate) using a wire bar so that the thickness after drying was 7 μm, and the solvent was dried at 100 ° C. for 2 minutes. The first to fifth ultraviolet irradiations shown in Table 1 were sequentially performed on the obtained film in an air atmosphere at 90 ° C. from the alignment substrate side.
[0139]
Next, a third ultraviolet ray irradiation was performed at 60 mW / cm from the alignment substrate side under a nitrogen atmosphere at 50 ° C.²  For 10 seconds to obtain a broadband cholesteric liquid crystal film having a selected wavelength of 410 to 965 nm. FIG. 4 shows the reflection spectrum of the broadband cholesteric liquid crystal film.
[0140]
A negative biaxial retardation plate was transferred onto the upper part of the obtained broadband cholesteric liquid crystal film (circularly polarized light reflecting plate) using a translucent adhesive. This negative biaxial retardation plate was obtained by the following method. That is, cyclohexanone as a solvent was added to 93 parts by weight of a photopolymerizable nematic liquid crystal monomer (LC242, manufactured by BASF) and 7 parts by weight of a polymerizable chiral agent (LC756, manufactured by BASF) as a solvent so as to have a concentration of 30% by weight. After adjusting and blending so that the center wavelength becomes 350 nm, a coating liquid was prepared by adding 5% by weight of Irgacure 907 as a photopolymerization initiator to the solid content described above, and the above solution was coated on a stretched polyethylene terephthalate substrate by wire. Using a bar, coating was performed so that the thickness after drying was 4 μm, and the solvent was dried at 100 ° C. for 2 minutes. Thereafter, the temperature was once raised to the isotropic transition temperature of the liquid crystal monomer, and then gradually cooled to form a layer having a uniform alignment state. 50 mW / cm²  For 5 seconds to fix the alignment state. When the phase difference of this negative biaxial retardation plate was measured, the phase difference was 120 nm when measured with the light having a wavelength of 550 nm inclined 2 ° in the front direction and 30 °. In addition, the measurement of the phase difference was performed by KOBRA-21ADH manufactured by Oji Scientific Instruments.
[0141]
Further, a circularly-polarized light reflecting plate similar to that described above was transferred and laminated on the upper portion using the same translucent adhesive to obtain a polarizing element. A λ / 4 plate (front retardation: 140 nm) obtained by uniaxially stretching a polycarbonate film was adhered to the obtained polarizing element to obtain a linear polarizing element. A polarizing plate (manufactured by Nitto Denko Corporation, TEG1465DU) was bonded to this linear polarizing element so that the transmission axis directions coincided with each other to obtain a polarizing plate integrated polarizing element.
[0142]
Example 2
The coating liquid prepared in Example 1 was applied on a stretched polyethylene terephthalate film (oriented substrate) using a wire bar so that the thickness after drying was 7 μm, and the solvent was dried at 100 ° C. for 2 minutes. Was. The first to fourth ultraviolet irradiations shown in Table 1 were sequentially performed on the obtained film in an air atmosphere at 90 ° C. from the alignment substrate side.
[0143]
Next, a third ultraviolet ray irradiation was performed at 60 mW / cm from the alignment substrate side under a nitrogen atmosphere at 50 ° C.²  For 10 seconds to obtain a broadband cholesteric liquid crystal film having a selected wavelength of 415 to 930 nm. FIG. 5 shows the reflection spectrum of the broadband cholesteric liquid crystal film.
[0144]
A negative biaxial retardation plate similar to that in Example 1 was transferred onto the upper portion of the obtained broadband cholesteric liquid crystal film (circularly polarized light reflecting plate) using a translucent adhesive. Further, a circularly-polarized light reflecting plate similar to that described above was transferred and laminated on the upper portion using the same light-transmitting adhesive to obtain a polarizing element. A λ / 4 plate (front retardation: 140 nm) obtained by uniaxially stretching a polycarbonate film was adhered to the obtained polarizing element to obtain a linear polarizing element. Further, a λ / 2 plate (front retardation: 270 nm) obtained by uniaxially stretching the polycarbonate film was adhered onto the λ / 4 plate to obtain a linearly polarizing element. A polarizing plate (manufactured by Nitto Denko Corporation, TEG1465DU) was bonded to this linear polarizing element so that the transmission axis directions coincided with each other to obtain a polarizing plate integrated polarizing element. These laminations were performed as shown in FIG. 3 in which the angle between the stretching axis (slow axis) of the λ / 4 plate and the λ / 2 plate and the stretching axis (absorption axis) of the polarizing plate.
[0145]
Example 3
Photopolymerizable mesogen compound (polymerizable nematic liquid crystal monomer, compound (1) of the above formula 4, molar extinction coefficient: 220 dm³  mol^-1cm^-1@ 365 nm. ) 94.8 parts by weight and 5.2 parts by weight of a polymerizable chiral agent (LC756 manufactured by BASF) and a solvent (cyclopentanone) were adjusted and blended so that the central wavelength of selective reflection became 550 nm. A coating solution (solid content: 30% by weight) was prepared by adding 0.3% by weight of a photopolymerization initiator (Irgacure 369, manufactured by Ciba Specialty Chemicals). The coating liquid was applied on a stretched polyethylene terephthalate film (oriented substrate) using a wire bar so that the thickness after drying was 7 μm, and the solvent was dried at 100 ° C. for 2 minutes. The first to fifth ultraviolet irradiations shown in Table 1 were sequentially performed on the obtained film from the alignment substrate side in an air atmosphere at 90 ° C.
[0146]
Next, a third ultraviolet ray irradiation is performed at 60 mW / cm from the alignment substrate side under a nitrogen atmosphere at 50 ° C.²  For 10 seconds to obtain a broadband cholesteric liquid crystal film having a selected wavelength of 420 to 890 nm. FIG. 6 shows the reflection spectrum of the broadband cholesteric liquid crystal film.
[0147]
A negative biaxial retardation plate similar to that in Example 1 was transferred onto the upper portion of the obtained broadband cholesteric liquid crystal film (circularly polarized light reflecting plate) using a translucent adhesive. Further, a circularly-polarized light reflecting plate similar to that described above was transferred and laminated on the upper portion using the same light-transmitting adhesive to obtain a polarizing element. A λ / 4 plate (front retardation: 125 nm, Nz coefficient: −1.0) obtained by biaxially stretching the polycarbonate film was bonded to the obtained polarizing element to obtain a linear polarizing element. A polarizing plate (manufactured by Nitto Denko Corporation, TEG1465DU) was bonded to this linear polarizing element so that the transmission axis directions coincided with each other to obtain a polarizing plate integrated polarizing element.
[0148]
Comparative Example 1
The coating solution prepared in Example 1 was applied on a stretched polyethylene terephthalate film (oriented substrate) using a wire bar so that the thickness after drying was 5 μm, and the solvent was dried at 100 ° C. for 2 minutes. Was. The obtained film is irradiated with 50 mW / cm of the first ultraviolet ray from the alignment substrate side in an air atmosphere at 60 ° C.²  For 10 seconds. Next, under a nitrogen atmosphere at 50 ° C., ultraviolet irradiation was performed from the alignment substrate side at 60 mW / cm²  For 10 seconds to obtain a broadband cholesteric liquid crystal film having a selected wavelength of 435 to 835 nm. FIG. 7 shows the reflection spectrum of the broadband cholesteric liquid crystal film.
[0149]
A negative biaxial retardation plate similar to that in Example 1 was transferred onto the upper portion of the obtained broadband cholesteric liquid crystal film (circularly polarized light reflecting plate) using a translucent adhesive. Further, a circularly-polarized light reflecting plate similar to that described above was transferred and laminated on the upper portion using the same light-transmitting adhesive to obtain a polarizing element. A λ / 4 plate (front retardation: 140 nm) obtained by uniaxially stretching a polycarbonate film was adhered to the obtained polarizing element to obtain a linear polarizing element. A polarizing plate (manufactured by Nitto Denko Corporation, TEG1465DU) was bonded to this linear polarizing element so that the transmission axis directions coincided with each other to obtain a polarizing plate integrated polarizing element.
[0150]
Comparative Example 2
The coating liquid prepared in Example 1 was applied on a stretched polyethylene terephthalate film (oriented substrate) using a wire bar so that the thickness after drying was 7 μm, and the solvent was dried at 100 ° C. for 2 minutes. Was. The obtained film was irradiated with a first ultraviolet ray from the alignment substrate side at 40 ° C. in an air atmosphere at 40 mW / cm.²  For 1.2 seconds. Further, heat treatment was performed at 90 ° C. for 20 seconds. Next, under a nitrogen atmosphere at 50 ° C., ultraviolet irradiation was performed from the alignment substrate side at 60 mW / cm²  For 10 seconds to obtain a broadband cholesteric liquid crystal film having a selected wavelength of 415 to 710 nm. FIG. 8 shows the reflection spectrum of the broadband cholesteric liquid crystal film.
[0151]
A negative biaxial retardation plate similar to that in Example 1 was transferred onto the upper portion of the obtained broadband cholesteric liquid crystal film (circularly polarized light reflecting plate) using a translucent adhesive. Further, a circularly-polarized light reflecting plate similar to that described above was transferred and laminated on the upper portion using the same light-transmitting adhesive to obtain a polarizing element. A λ / 4 plate (front retardation: 140 nm) obtained by uniaxially stretching a polycarbonate film was adhered to the obtained polarizing element to obtain a linear polarizing element. A polarizing plate (manufactured by Nitto Denko Corporation, TEG1465DU) was bonded to this linear polarizing element so that the transmission axis directions coincided with each other to obtain a polarizing plate integrated polarizing element.
[0152]
Comparative Example 3
The coating liquid prepared in Example 1 was applied on a stretched polyethylene terephthalate film (oriented substrate) using a wire bar so that the thickness after drying was 7 μm, and the solvent was dried at 100 ° C. for 2 minutes. Was. The first to fifth UV irradiations shown in Table 1 were sequentially performed on the obtained film in an air atmosphere at 90 ° C. from the alignment substrate side to obtain a broadband cholesteric liquid crystal film having a selected wavelength of 410 to 965 nm. . FIG. 9 shows the reflection spectrum of the broadband cholesteric liquid crystal film.
[0153]
A negative biaxial retardation plate similar to that in Example 1 was transferred onto the upper portion of the obtained broadband cholesteric liquid crystal film (circularly polarized light reflecting plate) using a translucent adhesive. Further, a circularly-polarized light reflecting plate similar to that described above was transferred and laminated on the upper portion using the same light-transmitting adhesive to obtain a polarizing element. A λ / 4 plate (front retardation: 140 nm) obtained by uniaxially stretching a polycarbonate film was adhered to the obtained polarizing element to obtain a linear polarizing element. A polarizing plate (manufactured by Nitto Denko Corporation, TEG1465DU) was bonded to this linear polarizing element so that the transmission axis directions coincided with each other to obtain a polarizing plate integrated polarizing element.
[0154]
(Liquid crystal display)
The polarizing element integrated with the polarizing plate obtained in each example was used as a lower plate of a TFT-LCD, while spherical silica particles (refractive index) were placed in an acrylic adhesive (thickness 25 μm, refractive index 1.47) on the upper plate side. A polarizing plate (TEG1465DU, manufactured by Nitto Denko Corporation) was laminated using a light-scattering adhesive (haze 80%) in which 20% by weight of a material having a ratio of 1.44 and a diameter of 4 μm was embedded.
[0155]
Further, a cold cathode tube having a diameter of about 3 mm was arranged on a side surface of a light guide having a fine prism structure on the lower surface, and covered with a light source holder made of a silver vapor-deposited polyethylene terephthalate film. A silver-deposited polyethylene terephthalate film reflector was disposed on the lower surface of the light guide plate, and a polyethylene terephthalate film having a scattering layer made of styrene beads formed on the surface was disposed on the upper surface of the light guide plate. This was disposed below the polarizing plate integrated polarizing element as a light source.
[0156]
FIG. 1 shows a case where the polarizing plate-integrated polarizing elements of Examples 1 and 3 and Comparative Examples 1 to 3 are used, and FIG. 2 shows a case where the polarizing plate-integrated polarizing element of Example 2 is used.
[0157]
<Evaluation method>
The broadband cholesteric liquid crystal film (circularly polarizing reflector) and polarizing plate integrated polarizing element obtained above were evaluated as follows. Table 1 shows the results. Table 1 also shows the conditions of each step in the examples and comparative examples.
[0158]
(Selective reflection wavelength band and bandwidth (△ λ))
The reflection spectrum of the broadband cholesteric liquid crystal film was measured with a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., Instant Multisystem MCPD2000) to determine the selective reflection wavelength band and the half-value width Δλ. The half-value width Δλ was defined as a reflection band at a half reflectance of the maximum reflectance.
[0159]
(Pitch change)
Pitch lengths near the UV-irradiated surface of the broadband cholesteric liquid crystal film (1 μm below the UV-irradiated surface), near the air interface (1 μm below the air interface), and the intermediate pitch length were measured.
[0160]
(reliability)
When each of the broadband cholesteric liquid crystal films was put into a reliability test of 90% RH at 80 ° C. and 60 ° C. for 500 hours, it was evaluated whether or not powdery substances were deposited on the surface.
[0161]
：: No precipitate.
×: Precipitates.
[0162]
(Front brightness)
The polarizing plate integrated type polarizing element was placed on a dot printing type backlight so that the polarizing plate side of the polarizing element was turned up, and evaluated by a luminance meter (BM-7, manufactured by TOPCON).
[0163]
(Slanted color change)
The oblique color tone change of the liquid crystal display device was evaluated according to the following criteria using a viewing angle measuring device EZ-CONTRAST manufactured by ELDIM.
Δxy = ((x₀  -X₁  )²  + (Y₀  -Y₁  )²  )^0.5
Front chromaticity (x₀  , Y₀  ), Chromaticity (x₁  , Y₁  )
Good: Color tone change Δxy at a viewing angle of 60 ° is less than 0.04.
Poor: color tone change Δxy at a viewing angle of 60 ° was 0.04 or more.
[0164]
[Table 1]

In the example, a cholesteric liquid crystal film having a selective reflection wavelength in a wide band including a long wavelength region is obtained. The cholesteric liquid crystal film has high reliability, and a polarizing element using the cholesteric liquid crystal film as a circularly polarizing plate is also excellent in luminance enhancement characteristics. In addition, the liquid crystal display device using the polarizing element distributes display information in a region where the gradation is not inverted by light diffusion in an oblique direction, so that a liquid crystal display device having a wide viewing angle in which a color change or a gradation inversion from an oblique direction is less likely to occur. Obtainable.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a viewing angle widening liquid crystal display device using polarizing plates integrated with polarizing plates of Examples 1 and 3 and Comparative Examples 1 to 3.
FIG. 2 is a conceptual diagram of a viewing angle widening liquid crystal display device using a polarizing element integrated with a polarizing plate of Example 2.
FIG. 3 is a diagram illustrating an axis angle of each layer in a polarizing plate integrated polarizing element of Example 2.
FIG. 4 is a reflection spectrum of the cholesteric liquid crystal film produced in Example 1.
FIG. 5 is a reflection spectrum of the cholesteric liquid crystal film produced in Example 2.
FIG. 6 is a reflection spectrum of a cholesteric liquid crystal film produced in Example 3.
FIG. 7 is a reflection spectrum of the cholesteric liquid crystal film produced in Comparative Example 1.
FIG. 8 is a reflection spectrum of the cholesteric liquid crystal film produced in Comparative Example 2.
FIG. 9 is a reflection spectrum of a cholesteric liquid crystal film produced in Comparative Example 3.

Claims (20)

A step of applying a liquid crystal mixture containing a polymerizable mesogen compound (A) and a polymerizable chiral agent (B) to an alignment substrate, and a step of irradiating the liquid crystal mixture with ultraviolet rays to carry out polymerization and curing; A method for producing a broadband cholesteric liquid crystal film having
The ultraviolet polymerization step,
In a state where the liquid crystal mixture is in contact with a gas containing oxygen, an ultraviolet irradiation intensity of 1 to 200 mW / cm ^{2 and} an ultraviolet irradiation within a range of 0.2 to 30 seconds are performed at a temperature of 20 ° C. or more, Each time the ultraviolet irradiation intensity is lowered and the ultraviolet irradiation time is increased, the ultraviolet irradiation is performed three times or more from the alignment substrate side (1),
Next, a method for producing a broadband cholesteric liquid crystal film, comprising a step (2) of irradiating ultraviolet rays in the absence of oxygen. 2. The method for producing a broadband cholesteric liquid crystal film according to claim 1, wherein the pitch length of the cholesteric liquid crystal film changes so as to continuously narrow from the alignment substrate side. 3. The broadband cholesteric liquid crystal according to claim 1, wherein the polymerizable mesogen compound (A) has one polymerizable functional group, and the polymerizable chiral agent (B) has two or more polymerizable functional groups. Film production method. Molar extinction coefficient of the polymerizable mesogen compound (A) The method for ^producing a broad band cholesteric liquid crystal film according to claim 1, characterized in that the 50~500dm ³ mol ^-1 cm ^-1 @ 365nm . The polymerizable mesogen compound (A) has the following general formula (1):

(Wherein R ₁ represents a hydrogen atom or a methyl group; n represents an integer of 1 to 5). A broadband cholesteric according to any one of claims 1 to 4, wherein Liquid crystal film manufacturing method. A circularly polarizing plate using a broadband cholesteric liquid crystal film obtained by the production method according to claim 1. Between at least two layers of reflective polarizers (a) in which the wavelength bands of selective reflection of polarized light overlap each other;
A retardation layer (b) having a front phase difference (normal direction) of substantially zero and having a phase difference of λ / 8 or more with respect to incident light incident at an angle of 30 ° or more with respect to the normal direction is disposed. A polarizing element,
A polarizing element, wherein the reflective polarizer (a) is the circularly polarizing plate according to claim 6. The polarizing element according to claim 7, wherein the selective reflection wavelengths of the at least two layers of the reflective polarizer (a) overlap each other in a wavelength range of 550 nm ± 10 nm. A phase difference layer (b) in which the planar orientation of a cholesteric liquid crystal phase having a selective reflection wavelength range other than the visible light range is fixed,
Fixed homeotropic alignment state of rod-shaped liquid crystal,
Discotic liquid crystal with a fixed nematic or columnar phase alignment state,
Biaxially oriented polymer film, or
9. The polarizing element according to claim 7, wherein an inorganic layered compound having a negative uniaxial property is fixedly oriented so that an optical axis is in a direction normal to a surface. A linearly polarizing element, characterized in that a λ / 4 plate is laminated on the circularly polarizing plate according to claim 6 or the polarizing element according to any one of claims 7 to 9 so that linearly polarized light can be obtained by transmission. . The linear polarizing element according to claim 10, which is obtained by laminating a cholesteric liquid crystal film, which is a circular polarizing plate, on a λ / 4 plate so that the pitch length is continuously narrowed. The linear polarizing element according to claim 10 or 11, wherein the λ / 4 plate is a retardation plate having a viewing angle improved by performing biaxial stretching to correct a phase difference of obliquely incident light. The linear polarizing element according to claim 10 or 11, wherein the λ / 4 plate is a liquid crystal polymer type retardation plate obtained by coating and fixing a nematic liquid crystal or a smectic liquid crystal. When the λ / 4 plate has an in-plane main refractive index of nx and ny and a thickness direction main refractive index of nz, the Nz coefficient defined by the formula: (nx−nz) / (nx−ny) becomes The linear polarizing element according to any one of claims 10 to 13, which satisfies -0.5 to -2.5. A linear polarizing element according to claim 10, wherein a λ / 2 plate is further laminated on the λ / 4 plate of the linear polarizing element according to claim 10. 16. A linearly polarized light, characterized in that an absorption polarizer whose transmission axis and transmission axis direction of the linearly polarizing element according to claim 10 are aligned on the λ / 4 plate side of the linearly polarizing element. element. The circularly polarizing plate according to claim 6, the polarizing element according to any one of claims 7 to 9, or the linearly polarized light according to any one of claims 10 to 16 on a front surface side of a surface light source having a reflective layer on a back surface side. A lighting device comprising an element. A liquid crystal display device comprising a liquid crystal cell on the light emitting side of the lighting device according to claim 17. 19. The viewing angle widening liquid crystal display device according to claim 18, wherein a viewing angle widening film for diffusing light on the viewing side transmitted through the liquid crystal cell is arranged on the viewing side with respect to the liquid crystal cell. 20. The viewing angle widening liquid crystal display device according to claim 19, wherein a diffusion plate having substantially no back scattering and no depolarization is used as the viewing angle widening film.

Images