JP3920078B2 - Optical compensation sheet and liquid crystal display device - Google Patents

Description

【００６０】
架橋性官能基は、配向膜ポリマーの主鎖に直結させても、連結基を介して結合させてもよい。
連結基は、アルキレン基、アリーレン基、−ＣＯ−、−ＮＨ−、−Ｏ−、−Ｓ−およびそれらの組み合わせからなる群より選ばれる二価の連結基であることが好ましい。アルキレン基の炭素原子数は、１乃至１２であることが好ましい。アリーレン基は、フェニレンであることが好ましい。
【００６１】
配向膜ポリマー（特にポリビニルアルコールを主鎖とするポリマー）は、上記の架橋性官能基とは別に、架橋剤を用いて架橋させることもできる。
架橋剤としては、アルデヒド類、Ｎ−メチロール化合物、ジオキサン誘導体、カルボキシル基を活性化することにより作用する化合物、活性ビニル化合物、活性ハロゲン化合物、イソオキサゾール類やジアルデヒド澱粉を用いることができる。アルデヒド類の例には、ホルムアルデヒド、グリオキザールおよびグルタルアルデヒドが含まれる。Ｎ−メチロール化合物の例には、ジメチロール尿素およびメチロールジメチルヒダントインが含まれる。ジオキサン誘導体の例には、２，３−ジヒドロキシジオキサンが含まれる。カルボキシル基を活性化することにより作用する化合物の例には、カルベニウム、２−ナフタレンスルホナート、１，１−ビスピロリジノ−１−クロロピリジニウムおよび１−モルホリノカルボニル−３−（スルホナトアミノメチル）が含まれる。活性ビニル化合物の例には、１，３，５−トリアクロイル−ヘキサヒドロ−ｓ−トリアジン、ビス（ビニルスルホン）メタンおよびＮ，Ｎ’−メチレンビス−［β−（ビニルスルホニル）プロピオンアミド］が含まれる。活性ハロゲン化合物の例には、２，４−ジクロロ−６−ヒドロキシ−Ｓ−トリアジンが含まれる。アルデヒド類が好ましく、グルタルアルデヒドが特に好ましい。二種類以上の架橋剤を併用してもよい。
【００６２】
架橋剤の添加量は、ポリマーの０．１乃至２０質量％の範囲であることが好ましく、０．５乃至１５質量％の範囲であることがさらに好ましい。配向膜中に残存する未反応の架橋剤は、配向膜の１．０質量％以下であることが好ましく、０．５質量％以下であることがさらに好ましい。
配向膜の形成では、配向膜ポリマーを含む塗布液を透明支持体上に塗布する。塗布液の溶媒としては、有機溶媒（例、メタノール）または水と有機溶媒との混合溶媒が好ましい。塗布方法としては、スピンコーティング法、ディップコーティング法、カーテンコーティング法、エクストルージョンコーティング法、バーコーティング法あるいはＥ型塗布法を採用できる。Ｅ型塗布法が特に好ましい。塗布膜の乾燥温度は、２０乃至１１０℃であることが好ましく、６０乃至１００℃であることがさらに好ましく、８０乃至１００℃の範囲であることが最も好ましい。乾燥時間は、１分乃至３６時間であることが好ましく、５乃至３０分であることがさらに好ましい。
【００６３】
ラビング処理は、公知の方法により実施できる。すなわち、配向膜の表面を、紙、布（ガーゼ、フェルト、ナイロン、ポリエステル繊維）あるいはゴムを用いて一定方向に擦ることにより、配向機能を得る。一般的には、長さ及び太さが均一な繊維を平均的に植毛した布を用いて数回程度ラビングを行う。
次に、配向膜を機能させて、配向膜の上に設けられる光学異方性層の液晶性分子を配向させる。その後、必要に応じて、配向膜ポリマーと光学異方性層に含まれる多官能モノマーとを反応させるか、あるいは、架橋剤を用いて配向膜ポリマーを架橋させる。
配向膜の膜厚は、０．１乃至１０μｍの範囲にあることが好ましい。
【００６４】
［光学異方性層］
光学異方性層は、液晶性分子から形成する。液晶性分子としては、棒状液晶性分子またはディスコティック液晶性分子を用いることが好ましい。
棒状液晶性分子としては、アゾメチン類、アゾキシ類、シアノビフェニル類、シアノフェニルエステル類、安息香酸エステル類、シクロヘキサンカルボン酸フェニルエステル類、シアノフェニルシクロヘキサン類、シアノ置換フェニルピリミジン類、アルコキシ置換フェニルピリミジン類、フェニルジオキサン類、トラン類およびアルケニルシクロヘキシルベンゾニトリル類が好ましく用いられる。なお、棒状液晶性分子には、金属錯体も含まれる。
棒状液晶性分子については、季刊化学総説第２２巻液晶の化学（１９９４年）日本化学会編の第４章、第７章および第１１章、および液晶デバイスハンドブック日本学術振興会第１４２委員会編の第３章に記載がある。
ディスコティック液晶性分子も、様々な文献（C. Destrade et al., Mol. Crysr. Liq. Cryst., vol. 71, page 111 (1981) ；日本化学会編、季刊化学総説、Ｎｏ．２２、液晶の化学、第５章、第１０章第２節(1994)；B. Kohne et al., Angew. Chem. Soc. Chem. Comm., page 1794 (1985)；J. Zhang et al., J. Am. Chem. Soc., vol. 116, page 2655 (1994)）に記載されている。
【００６５】
液晶性分子は重合性官能基として二重結合を有することが好ましい。二重結合を重合性官能基として液晶性分子に導入すると、光学異方性層に含まれる多官能モノマーと液晶性分子を共重合させることができる。その結果、多官能モノマーと多官能モノマーとの間だけではなく、液晶性分子と液晶性分子との間、そして多官能モノマーと液晶性分子との間も共有結合で強固に結合される。従って、架橋性官能基を液晶性分子に導入することで、光学補償シートの強度を著しく改善することができる。
【００６６】
ディスコティック液晶性分子では、円盤状コアに重合性官能基を直結させると、重合反応において配向状態を保つことが困難になる。そこで、円盤状コアと重合性官能基との間に、連結基を導入する。従って、重合性官能基を有するディスコティック液晶性分子は、下記式（Ｉ）で表わされる化合物であることが好ましい。
【００６７】
（Ｉ） Ｄ（−Ｌ−Ｑ）_n
式（Ｉ）において、Ｄは、円盤状コアであり；Ｌは、二価の連結基であり；Ｑは、重合性官能基であり；そして、ｎは、４乃至１２の整数である。
円盤状コア（Ｄ）の例を以下に示す。以下の各例において、ＬＱ（またはＱＬ）は、二価の連結基（Ｌ）と重合性基（Ｑ）との組み合わせを意味する。
【００６８】
【化２】

【００６９】
【化３】

【００７０】
【化４】

【００７１】
【化５】

【００７２】
【化６】

【００７３】
【化７】

【００７４】
【化８】

【００７５】
式（Ｉ）において、二価の連結基（Ｌ）は、アルキレン基、アルケニレン基、アリーレン基、−ＣＯ−、−ＮＨ−、−Ｏ−、−Ｓ−およびそれらの組み合わせからなる群より選ばれる二価の連結基であることが好ましい。二価の連結基（Ｌ）は、アルキレン基、アリーレン基、−ＣＯ−、−ＮＨ−、−Ｏ−および−Ｓ−からなる群より選ばれる二価の基を少なくとも二つ組み合わせた二価の連結基であることがさらに好ましい。二価の連結基（Ｌ）は、アルキレン基、アリーレン基、−ＣＯ−および−Ｏ−からなる群より選ばれる二価の基を少なくとも二つ組み合わせた二価の連結基であることが最も好ましい。アルキレン基の炭素原子数は、１乃至１２であることが好ましい。アルケニレン基の炭素原子数は、２乃至１２であることが好まし。アリーレン基の炭素原子数は、６乃至１０であることが好ましい。
【００７６】
二価の連結基（Ｌ）の例を以下に示す。左側が円盤状コア（Ｄ）に結合し、右側が重合性基（Ｑ）に結合する。ＡＬはアルキレン基またはアルケニレン基、ＡＲはアリーレン基を意味する。なお、アルキレン基、アルケニレン基およびアリーレン基は、置換基（例、アルキル基）を有していてもよい。
Ｌ１：−ＡＬ−ＣＯ−Ｏ−ＡＬ−
Ｌ２：−ＡＬ−ＣＯ−Ｏ−ＡＬ−Ｏ−
Ｌ３：−ＡＬ−ＣＯ−Ｏ−ＡＬ−Ｏ−ＡＬ−
Ｌ４：−ＡＬ−ＣＯ−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ５：−ＣＯ−ＡＲ−Ｏ−ＡＬ−
Ｌ６：−ＣＯ−ＡＲ−Ｏ−ＡＬ−Ｏ−
Ｌ７：−ＣＯ−ＡＲ−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ８：−ＣＯ−ＮＨ−ＡＬ−
Ｌ９：−ＮＨ−ＡＬ−Ｏ−
Ｌ10：−ＮＨ−ＡＬ−Ｏ−ＣＯ−
【００７７】
Ｌ11：−Ｏ−ＡＬ−
Ｌ12：−Ｏ−ＡＬ−Ｏ−
Ｌ13：−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ14：−Ｏ−ＡＬ−Ｏ−ＣＯ−ＮＨ−ＡＬ−
Ｌ15：−Ｏ−ＡＬ−Ｓ−ＡＬ−
Ｌ16：−Ｏ−ＣＯ−ＡＲ−Ｏ−ＡＬ−ＣＯ−
Ｌ17：−Ｏ−ＣＯ−ＡＲ−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ18：−Ｏ−ＣＯ−ＡＲ−Ｏ−ＡＬ−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ19：−Ｏ−ＣＯ−ＡＲ−Ｏ−ＡＬ−Ｏ−ＡＬ−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ20：−Ｓ−ＡＬ−
Ｌ21：−Ｓ−ＡＬ−Ｏ−
Ｌ22：−Ｓ−ＡＬ−Ｏ−ＣＯ−
Ｌ23：−Ｓ−ＡＬ−Ｓ−ＡＬ−
Ｌ24：−Ｓ−ＡＲ−ＡＬ−
【００７８】
式（Ｉ）の重合性官能基（Ｑ）の例は、配向膜ポリマーについて説明した重合性官能基の例（Ｑ１〜Ｑ６）と同様である。
式（Ｉ）において、ｎは４乃至１２の整数である。具体的な数字は、円盤状コア（Ｄ）の種類に応じて決定される。なお、複数のＬとＱの組み合わせは、異なっていてもよいが、同一であることが好ましい。
【００７９】
光学異方性層は、液晶性分子および必要に応じて重合性開始剤や任意の成分を含む塗布液を、配向膜の上に塗布することで形成できる。
光学異方性層の厚さは、０．５乃至１００μｍであることが好ましく、０．５乃至３０μｍであることがさらに好ましい。
【００８０】
光学異方性層を形成後、多官能モノマーを重合させる。配向膜ポリマーあるいは液晶性分子が重合性基を有する場合は、多官能モノマーと共重合させる。
重合反応には、熱重合開始剤を用いる熱重合反応と光重合開始剤を用いる光重合反応とが含まれる。光重合反応が好ましい。
光重合開始剤の例には、α−カルボニル化合物（米国特許２３６７６６１号、同２３６７６７０号の各明細書記載）、アシロインエーテル（米国特許２４４８８２８号明細書記載）、α−炭化水素置換芳香族アシロイン化合物（米国特許２７２２５１２号明細書記載）、多核キノン化合物（米国特許３０４６１２７号、同２９５１７５８号の各明細書記載）、トリアリールイミダゾールダイマーとｐ−アミノフェニルケトンとの組み合わせ（米国特許３５４９３６７号明細書記載）、アクリジンおよびフェナジン化合物（特開昭６０−１０５６６７号公報、米国特許４２３９８５０号明細書記載）およびオキサジアゾール化合物（米国特許４２１２９７０号明細書記載）が含まれる。
光重合開始剤の使用量は、塗布液の固形分の０．０１乃至２０質量％であることが好ましく、０．５乃至５質量％であることがさらに好ましい。
重合のための光照射は、紫外線を用いることが好ましい。
照射エネルギーは、２０乃至５０００ｍＪ／ｃｍ² であることが好ましく、１００乃至８００ｍＪ／ｃｍ² であることがさらに好ましい。また、光重合反応を促進するため、加熱条件下で光照射を実施してもよい。
保護層を、光学異方性層の上に設けてもよい。
【００８１】
［偏光板］
偏光板は、偏光膜およびその両側に配置された二枚の透明保護膜からなる。透明保護膜としては、一般にセルロースアセテートフイルムが用いられる。前述したように、光学補償シートの透明支持体を一方の保護膜として用いることができる。この場合、光学補償シートと偏光板とは、一体化（通常は楕円偏光板として機能）する。一体型楕円偏光板では、光学補償シートの透明支持体の遅相軸と偏光膜の透過軸とは、実質的に平行になるように配置する。
透明保護膜の透湿性は１００乃至１０００（ｇ／ｍ² ）／２４ｈｒｓの範囲であることが好ましく、３００乃至７００（ｇ／ｍ² ）／２４ｈｒｓの範囲であることがさらに好ましい。
偏光膜には、ヨウ素系偏光膜、二色性染料を用いる染料系偏光膜やポリエン系偏光膜がある。ヨウ素系偏光膜および染料系偏光膜は、一般にポリビニルアルコール系フイルムを用いて製造する。
【００８２】
［液晶表示装置］
光学補償シートまたは光学補償シートを有する偏光板は、液晶表示装置、特に透過型液晶表示装置に有利に用いられる。
透過型液晶表示装置は、液晶セルおよびその両側に配置された二枚の偏光板からなる。液晶セルは、二枚の電極基板の間に液晶を担持している。
光学補償シートを液晶表示装置に用いる場合は、液晶セルと一方の偏光板との間に、本発明に従う光学補償シートを一枚配置するか、あるいは液晶セルと双方の偏光板との間に本発明に従う光学補償シートを二枚配置する。
偏光板を液晶表示装置に用いる場合は、二枚の偏光板の一方の代わりとして本発明に従う光学補償シートを有する偏光板を用いればよい。双方の偏光板の代わりに本発明に従う光学補償シートを有する偏光板を用いてもよい。本発明に従う光学補償シートを有する偏光板を液晶表示装置に用いる場合、偏光板を、その保護膜として用いられている光学補償シートが液晶セル側となるように配置する。
【００８３】
液晶セルは、ＴＮモード、ＥＣＢモード、ＶＡモード、またはＯＣＢモードであることが好ましい。ＶＡモードには、ＭＶＡモードが含まれる。
ＴＮモードの液晶セルでは、電圧無印加時に棒状液晶性分子が実質的に水平配向し、さらに６０乃至１２０゜にねじれ配向している。
ＴＮモードの液晶セルは、カラーＴＦＴ液晶表示装置として最も多く利用されており、多数の文献に記載がある。
【００８４】
ＶＡモードの液晶セルでは、電圧無印加時に棒状液晶性分子が実質的に垂直に配向している。
ＶＡモードの液晶セルには、（１）棒状液晶性分子を電圧無印加時に実質的に垂直に配向させ、電圧印加時に実質的に水平に配向させる狭義のＶＡモードの液晶セル（特開平２−１７６６２５号公報記載）に加えて、（２）視野角拡大のため、ＶＡモードをマルチドメイン化した（ＭＶＡモードの）液晶セル（ＳＩＤ９７、Digest of tech. Papers（予稿集）２８（１９９７）８４５記載）、（３）棒状液晶性分子を電圧無印加時に実質的に垂直配向させ、電圧印加時にねじれマルチドメイン配向させるモード（ｎ−ＡＳＭモード）の液晶セル（日本液晶討論会の予稿集５８〜５９（１９９８）記載）、（４）ＳＵＲＶＡＩＶＡＬモードの液晶セル（ＬＣＤインターナショナル９８で発表）および（５）ＣＰＡモードの液晶セル（ＳＩＤ０１で発表）が含まれる。
【００８５】
ＯＣＢモードの液晶セルは、棒状液晶性分子を液晶セルの上部と下部とで実質的に逆の方向に（対称的に）配向させるベンド配向モードの液晶セルである。ベンド配向モードの液晶セルを用いた液晶表示装置は、米国特許４５８３８２５号、同５４１０４２２号の各明細書に開示されている。棒状液晶性分子が液晶セルの上部と下部とで対称的に配向しているため、ベンド配向モードの液晶セルは、自己光学補償機能を有する。そのため、この液晶モードは、ＯＣＢ(Optically Compensatory Bend) 液晶モードとも呼ばれる。ベンド配向モードの液晶表示装置は、応答速度が速いとの利点がある。
ＴＮモードの液晶セルは、カラーＴＦＴ液晶表示装置として最も多く利用されており、多数の文献に記載がある。
ＥＣＢモードの液晶セルは、最も古くから研究されている液晶モードの一つであり、これも多数の文献に記載がある。
【００８６】
【実施例】
［実施例１］
（セルロースアセテート溶液の調製）
下記の組成物をミキシングタンクに投入し、加熱しながら攪拌して、各成分を溶解し、セルロースアセテート溶液を調製した。
【００８７】
────────────────────────────────────
セルロースアセテート溶液組成
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酢化度６０．９％のセルロースアセテート １００質量部
トリフェニルホスフェート（可塑剤） ７．８質量部
ビフェニルジフェニルホスフェート（可塑剤） ３．９質量部
メチレンクロライド（第１溶媒） ３００質量部
メタノール（第２溶媒） ５４質量部
１−ブタノール（第３溶媒） １１質量部
────────────────────────────────────
【００８８】
（レターデーション上昇剤溶液の調製）
別のミキシングタンクに、下記のレターデーション上昇剤１６質量部、メチレンクロライド８０質量部およびメタノール２０質量部を投入し、加熱しながら攪拌して、レターデーション上昇剤溶液を調製した。
【００８９】
【化９】

【００９０】
（透明支持体の作製）
セルロースアセテート溶液４７５質量部にレターデーション上昇剤溶液２５質量部を混合し、攪拌してドープを調製した。レターデーション上昇剤の添加量は、セルロースアセテート１００質量部に対して、３．０質量部であった。
得られたドープを、冷却ドラム流延機を用いて流延して、透明支持体として用いるセルロースアセテートフイルムを製造した。
作製したセルロースアセテートフイルムについて、エリプソメーター（Ｍ−１５０、日本分光（株）製）を用い、波長６３３ｎｍにおけるレターデーション値を測定したところ、Ｒｅレターデーション値は１０ｎｍ、Ｒthレターデーション値は８１ｎｍであった。
【００９１】
（下塗り層の形成）
透明支持体の一方の面に、下記の組成の塗布液を２８ｍｌ／ｍ² 塗布し、乾燥して、厚さ０．１μｍのゼラチン下塗り層を形成した。
【００９２】
────────────────────────────────────
下塗り層塗布液組成
────────────────────────────────────
ゼラチン ０．５４２質量部
ホルムアルデヒド ０．１３５質量部
サリチル酸 ０．１６０質量部
アセトン ３９．１質量部
メタノール １５．８質量部
メチレンクロライド ４０．６質量部
水 １．２質量部
────────────────────────────────────
【００９３】
（第２下塗り層の形成）
下塗り層の上に、下記の組成の塗布液を７ｍｌ／ｍ² 塗布し、乾燥して、第２下塗り層を形成した。
【００９４】
────────────────────────────────────
第２下塗り層塗布液組成
────────────────────────────────────
下記のアニオン性コポリマー ０．０７９質量部
クエン酸モノエチルエステル １．０１質量部
アセトン ２０質量部
メタノール ８７．７質量部
水 ４．０５質量部
────────────────────────────────────
【００９５】
【化１０】

【００９６】
（バック層の形成）
下塗り層とは反対側の支持体面に、下記の組成の塗布液を２５ｍｌ／ｍ² 塗布し、乾燥して、バック層を形成した。
【００９７】
────────────────────────────────────
バック層塗布液組成
────────────────────────────────────
酢化度５５％のセルロースジアセテート ０．６５６質量部
平均粒径１μｍのシリカ系マット剤 ０．０６５質量部
アセトン ６７．９質量部
メタノール １０．４質量部
────────────────────────────────────
【００９８】
（配向膜の形成）
第２下塗り層の上に、下記の組成の塗布液を＃１６のワイヤーバーコーターで２８ｍｌ／ｍ² 塗布した。６０℃の温風で６０秒、さらに９０℃の温風で１５０秒乾燥した。
次に、セルロースアセテートフイルム（透明支持体）の長手方向に、形成した膜に対してラビング処理を実施した。
【００９９】

【０１００】
【化１１】

【０１０１】
（光学異方性層の形成）
配向膜の上に、下記のディスコティック液晶性分子４１．０１ｇ、エチレンオキサイド変成トリメチロールプロパントリアクリレート（Ｖ＃３６０、大阪有機化学（株）製）２．０３ｇ、ジペンタエリスリトールヘキサアクリレート（ＫＹＡＲＡＤ・ＤＰＨＡ、日本化薬（株）製）２．０３ｇ、セルロースアセテートブチレート（ＣＡＢ５５１−０．２、イーストマンケミカル社製）０．９０ｇ、セルロースアセテートブチレート（ＣＡＢ５３１−１、イーストマンケミカル社製）０．２３ｇ、光重合開始剤（イルガキュアー９０７、チバガイギー社製）１．３５ｇ、増感剤（カヤキュアーＤＥＴＸ、日本化薬（株）製）０．４５ｇを、１０２ｇのメチルエチルケトンに溶解した塗布液を、＃４のワイヤーバーで塗布した。これを金属の枠に貼り付けて、１３０℃の恒温槽中で２分間加熱し、ディスコティック液晶性分子を配向させた。次に、８０℃の雰囲気で膜面温度が約１００℃となる状態で、１２０Ｗ／ｃｍ高圧水銀灯を用いて、０．４秒間紫外線を照射し、ディスコティック液晶性分子、多官能モノマー（ジペンタエリスリトールヘキサアクリレート）および配向膜ポリマー（変性ポリビニルアルコール）とを共重合させた。その後、室温まで放冷した。このようにして、光学異方性層を形成して、光学補償シートを作製した。
波長６３３ｎｍで光学異方性層のレターデーション値を測定したところ、Ｒｅレターデーション値は４８ｎｍであった。また、ディスコティック液晶性分子の円盤面と透明支持体面との平均角度（平均傾斜角）は、４２゜であった。
【０１０２】
【化１２】

【０１０３】
（偏光板の作製）
延伸したポリビニルアルコールフイルムにヨウ素を吸着させて偏光膜を作製した。
次に、作製した光学補償シートの透明支持体バック層側を、ポリビニルアルコール系接着剤を用いて偏光膜の片側に貼り付けた。透明支持体の遅相軸と偏光膜の透過軸とが平行になるように配置した。
市販のセルローストリアセテートフイルム（フジタックＴＤ８０ＵＦ、富士写真フイルム（株）製）をケン化処理し、透明保護膜として、ポリビニルアルコール系接着剤を用いて、偏光膜の反対側（光学補償シートを貼り付けなかった側）に貼り付けた。透明保護膜の遅相軸と偏光膜の透過軸とは直交するように配置した。
このようにして、光学補償シート付きの偏光板を作製した。
【０１０４】
（リワーク性の評価）
作製した光学補償シート付きの偏光板を粘着剤を介してガラス板に貼り付けた。偏光板の光学補償シート側（光学異方性層側）がガラス面側となるように配置した。
ガラス板に貼り付けた光学補償シート付きの偏光板を、５０℃、５気圧で６時間エイジングを行った。２５℃、相対湿度６０℃の条件に戻して、光学補償シート付きの偏光板をガラス板から剥離した。
以上の試験操作を１００枚の偏光板について行ったところ、１００枚全ての偏光板を、ガラス板から問題なく（剥げ残りなく）剥離することができた。
【０１０５】
（液晶表示装置の作製）
市販のＴＮモードの液晶表示装置（６Ｅ−Ａ３、シャープ（株）製）に設けられている一対の偏光板を剥がし、代わりに作製した偏光板二枚を、光学補償シートが液晶セル側となるように粘着剤を介して貼り合わせた。このようにして液晶表示装置を作製した。観察者側の偏光板の透過軸と、バックライト側の透過軸とは、Ｏモードとなるように配置した。
作製した液晶表示装置について、測定機（ＥＺ−Contrast１６０Ｄ、ＥＬＤＩＭ社製）を用いて、黒表示（Ｌ１）から白表示（Ｌ８）までの８段階で視野角を測定した。具体的な視野角としては、コントラスト比が１０以上で、黒側の階調反転（Ｌ１とＬ２との間の反転）がない角度を求めた。その結果、上側で７０゜、下側で４５゜、そして左右で１６０゜との広い視野角が得られた。
【０１０６】
［実施例２］
（セルロースアセテート溶液の調製）
下記の組成物からなる二種類のセルロースアセテート溶液（内層用ドープおよび外層用ドープ）を調製した。内層用ドープは、５０℃にて絶対濾過精度０．０１ｍｍの濾紙（＃６３、東洋濾紙（株）製）にて濾過した。外層用ドープは、５０℃にて、絶対濾過精度０．００２５ｍｍの濾紙（ＦＨ０２５、ポール社製）にて濾過した。
【０１０７】
────────────────────────────────────
セルロースアセテート溶液組成 内層用ドープ 外層用ドープ
────────────────────────────────────
酢化度６０．５％セルロースアセテート １００質量部 １００質量部
トリフェニルホスフェート ７．８質量部 ７．８質量部
ビフェニルジフェニルホスフェート ３．９質量部 ３．９質量部
実施例１で用いたレターデーション上昇剤 ３．０質量部 ３．０質量部
メチレンクロライド（第１溶媒） ４５０質量部 ４８１質量部
メタノール（第２溶媒） ３９質量部 ４２質量部
────────────────────────────────────
【０１０８】
（透明支持体の作製）
三層共流延ダイを用いて、内層用ドープが内側に、外層用ドープがその両外側となるように配置して、金属支持体上に同時に吐出させて、重層流延した。流延量は、内層の層厚が４５μｍ、外層の層厚がそれぞれ５μｍとなるように設定した。流延膜を支持体から剥ぎ取り、テンターで３０％横に一軸延伸した後、乾燥して、セルロースアセテートフイルムを製造した。乾燥は、７０℃で３分、１２０℃で５分行った後、支持体からフイルムを剥ぎ取り、１３０℃で３０分、段階的に乾燥して、支持体として用いるセルロースアセテートフイルムを得た。残留溶媒量は、０．５質量％であった。
作製したセルロースアセテートフイルムについて、エリプソメーター（Ｍ−１５０、日本分光（株）製）を用い、波長６３３ｎｍにおけるレターデーション値を測定したところ、Ｒｅレターデーション値は３８ｎｍ、Ｒthレターデーション値は２３０ｎｍであった。
【０１０９】
（透明支持体の鹸化処理）
透明支持体を、２．０Ｎの水酸化カリウム水溶液に２５℃で２分間浸漬した後、硫酸で中和し、純水で水洗して、乾燥した。その後、透明支持体の表面エネルギーを接触角法により求めたところ、６３ｍＮ／ｍであった。
【０１１０】
（配向膜の形成）
鹸化処理した透明支持体の上に、実施例１で用いた組成の配向膜塗布液を＃１６のワイヤーバーコーターで２８ｍｌ／ｍ² 塗布した。６０℃の温風で６０秒、さらに９０℃の温風で１５０秒乾燥した。
次に、セルロースアセテートフイルム（透明支持体）の長手方向に対して４５゜の方向に、形成した膜に対してラビング処理を実施した。
【０１１１】
（光学異方性層の形成）
配向膜の上に、実施例１で用いたディスコティック液晶性分子４１．０１ｇ、エチレンオキサイド変成トリメチロールプロパントリアクリレート（Ｖ＃３６０、大阪有機化学（株）製）１．２２ｇ、多官能アクリレートモノマー（ＮＫエステル・Ａ−ＴＭＭＴ、新中村化学工業（株）製）２．８４ｇ、セルロースアセテートブチレート（ＣＡＢ５５１−０．２、イーストマンケミカル社製）０．９０ｇ、セルロースアセテートブチレート（ＣＡＢ５３１−１、イーストマンケミカル社製）０．２３ｇ、光重合開始剤（イルガキュアー９０７、チバガイギー社製）１．３５ｇ、増感剤（カヤキュアーＤＥＴＸ、日本化薬（株）製）０．４５ｇを、１０２ｇのメチルエチルケトンに溶解した塗布液を、＃４のワイヤーバーで塗布した。これを金属の枠に貼り付けて、１３０℃の恒温槽中で２分間加熱し、ディスコティック液晶性分子を配向させた。次に、８０℃の雰囲気で膜面温度が約１００℃となる状態で、１２０Ｗ／ｃｍ高圧水銀灯を用いて、０．４秒間紫外線を照射し、ディスコティック液晶性分子、多官能アクリレートモノマーおよび配向膜ポリマー（変性ポリビニルアルコール）とを共重合させた。その後、室温まで放冷した。このようにして、光学異方性層を形成して、光学補償シートを作製した。
波長６３３ｎｍで光学異方性層のレターデーション値を測定したところ、Ｒｅレターデーション値は４５ｎｍであった。また、ディスコティック液晶性分子の円盤面と透明支持体面との平均角度（平均傾斜角）は、３９゜であった。
【０１１２】
（偏光板の作製）
作製した光学補償シートを用いて、透明支持体の遅相軸と偏光膜の透過軸とが４５゜の角度となるように配置した以外は、実施例１と同様にして、偏光板を作製した。
【０１１３】
（リワーク性の評価）
作製した偏光板を粘着剤を介してガラス板に貼り付けた。光学補償シートがガラス面側となるように配置した。
ガラス板に貼り付けた偏光板を、５０℃、５気圧で６時間エイジングを行った。２５℃、相対湿度６０℃の条件に戻して、偏光板をガラス板から剥離した。
以上の試験操作を１００枚の偏光板について行ったところ、１００枚全ての偏光板を、ガラス板から問題なく（剥げ残りなく）剥離することができた。
【０１１４】
（ベンド配向液晶セルの作製）
ＩＴＯ電極付きのガラス基板に、ポリイミド膜を配向膜として設け、配向膜にラビング処理を行った。得られた二枚のガラス基板をラビング方向が平行となる配置で向かい合わせ、セルギャップを６μｍに設定した。セルギャップにΔｎが０．１３９６の棒状液晶性分子（ＺＬＩ１１３２、メルク社製）を注入し、ベンド配向液晶セルを作製した。
【０１１５】
（液晶表示装置の作製）
作製したベンド配向セルを挟むように、作製した偏光板を二枚貼り付けた。偏光板の光学異方性層がセル基板に対面し、液晶セルのラビング方向とそれに対面する光学異方性層のラビング方向とが反平行となるように配置した。
作製した液晶表示装置の液晶セルに、５５Ｈｚの矩形波電圧を印加した。白表示２Ｖ、黒表示５Ｖのノーマリーホワイトモードとした。透過率の比（白表示／黒表示）をコントラスト比として、測定機（ＥＺ−Contrast１６０Ｄ、ＥＬＤＩＭ社製）を用いて、黒表示（Ｌ１）から白表示（Ｌ８）までの８段階で視野角を測定した。具体的な視野角としては、コントラスト比が１０以上で、黒側の階調反転（Ｌ１とＬ２との間の反転）がない角度を求めた。その結果、上側で８０゜、下側で８０゜、そして左右で８０゜との広い視野角が得られた。
【０１１６】
［実施例３］
（セルロースアセテート溶液の調製）
下記の組成物からなるセルロースアセテート溶液（ドープ）を調製した。
【０１１７】
────────────────────────────────────
セルロースアセテート溶液組成
────────────────────────────────────
酢化度５９．５％のセルロースアセテート １００質量部
トリフェニルホスフェート ７．８質量部
ビフェニルジフェニルホスフェート ３．９質量部
実施例１で用いたレターデーション上昇剤 ２．０質量部
酢酸メチル ３０６質量部
シクロヘキサノン １２２質量部
メタノール ３０．５質量部
エタノール ３０．５質量部
平均粒径２０ｎｍのシリカ微粒子 １．０質量部
────────────────────────────────────
【０１１８】
（透明支持体の作製）
調製したドープを金属支持体上に流延した。７０℃で３分、１２０℃で５分乾燥した後、支持体からフイルムを剥ぎ取り、１３０℃で５０分乾燥して、支持体として用いるセルロースアセテートフイルムを得た。残留溶媒量は、０．８質量％であった。
作製したセルロースアセテートフイルムについて、エリプソメーター（Ｍ−１５０、日本分光（株）製）を用い、波長６３３ｎｍにおけるレターデーション値を測定したところ、Ｒｅレターデーション値は１０ｎｍ、Ｒthレターデーション値は５０ｎｍであった。
【０１１９】
（透明支持体の鹸化処理）
透明支持体に、２．０Ｎの水酸化カリウム水溶液を７０℃で塗布し、３０秒後に純水で水洗して、乾燥した。その後、透明支持体の表面エネルギーを接触角法により求めたところ、６５ｍＮ／ｍであった。
【０１２０】
（配向膜および光学異方性層の形成）
セルロースアセテートフイルムのケン化処理した側の面に、実施例１と同様にして（ただし下塗り層を設けずに）配向膜および光学異方性層を形成した。
このようにして、光学補償シートを作製した。
【０１２１】
［実施例４］
（透明支持体の鹸化処理）
実施例１で作製した透明支持体に、１．５Ｎの水酸化カリウム溶液（溶媒：水／イソプロピルアルコール／ポリエチレングリコール＝１４／８６／１５容量％）を５ｍｌ／ｍ² 塗布し、６０℃で約１０秒間保持した。フイルム表面に残った水酸化カリウムを水洗し、乾燥した。透明支持体の表面エネルギーを接触角法により求めたところ、６３ｍＮ／ｍであった。
【０１２２】
（配向膜および光学異方性層の形成）
セルロースアセテートフイルムのケン化処理した側の面に、実施例１と同様にして（ただし下塗り層を設けずに）配向膜および光学異方性層を形成した。
このようにして、光学補償シートを作製した。
【図面の簡単な説明】
【図１】透過型液晶表示装置の基本的な構成を示す模式図である。
【図２】透過型液晶表示装置の別の基本的な構成を示す模式図である。
【図３】透過型液晶表示装置のさらに別の基本的な構成を示す模式図である。
【図４】反射型液晶表示装置の基本的な構成を示す模式図である。
【符号の説明】
ＢＬ バックライト
ＲＰ 反射板
１、１ａ、１ｂ、３、３ａ、３ｂ 透明保護膜
２、２ａ、２ｂ 偏光膜
４、４ａ、４ｂ 透明支持体
５、５ａ、５ｂ 光学異方性層
６ａ、６ｂ 液晶セルの基板
７ 棒状液晶性分子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical compensation sheet having an optically anisotropic layer formed of liquid crystalline molecules and a transparent support, and a liquid crystal display device using the same.
[0002]
[Prior art]
The liquid crystal display device includes a liquid crystal cell and a polarizing plate. In the transmissive liquid crystal display device, two polarizing plates are attached to both sides of the liquid crystal cell. In a reflective liquid crystal display device, a reflector, a liquid crystal cell, and a single polarizing plate are arranged in this order.
The liquid crystal cell is composed of a rod-like liquid crystal molecule, two substrates for enclosing it, and an electrode layer for applying a voltage to the rod-like liquid crystal molecule. The liquid crystal cell is different in the alignment state of rod-like liquid crystal molecules. As for the transmissive type, TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), OCB (Optically Compensatory Bend), STN (STN) Various display modes such as HAN (Hybrid Aligned Nematic) and TN have been proposed for Supper Twisted Nematic (VA), VA (Vertically Aligned), and reflection type.
[0003]
In a normal liquid crystal display device, an optical compensation sheet (retardation plate) is used in addition to a liquid crystal cell and a polarizing plate. The optical compensation sheet is used for eliminating image coloring and expanding the viewing angle. In a transmissive liquid crystal display device, one or two optical compensation sheets are disposed between a liquid crystal cell and a polarizing plate. In the reflective liquid crystal display device, one optical compensation sheet is disposed between the liquid crystal cell and the polarizing plate.
As an optical compensation sheet, a stretched birefringent film has been conventionally used.
Recently, instead of an optical compensation sheet made of a stretched birefringent film, an optical compensation sheet having an optically anisotropic layer formed from liquid crystalline molecules (particularly discotic liquid crystalline molecules) on a transparent support is used. Has been proposed. The optically anisotropic layer is formed by aligning liquid crystal molecules and fixing the alignment state. Liquid crystalline molecules have a large birefringence. The liquid crystal molecules have various alignment forms. By using liquid crystalline molecules, it has become possible to realize optical properties that cannot be obtained with conventional stretched birefringent films.
[0004]
The optical properties of the optical compensation sheet are determined according to the optical properties of the liquid crystal cell, specifically, the display mode differences as described above. When a liquid crystal molecule, particularly a discotic liquid crystal molecule is used, an optical compensation sheet corresponding to various display modes of the liquid crystal cell (which can be optically compensated) can be produced.
Optical compensation sheets using discotic liquid crystalline molecules have already been proposed for various display modes. For example, an optical compensation sheet for a TN mode liquid crystal cell is described in each specification of JP-A-6-214116, US Pat. Nos. 5,583,679, 5,646,703, and German Patent 3,911,620A1. Further, an optical compensation sheet for liquid crystal cells in IPS mode or FLC mode is described in JP-A-10-54982. Furthermore, OCB mode or HAN mode liquid crystal cell optical compensation sheets are described in US Pat. No. 5,805,253 and International Patent Application WO 96/37804. Furthermore, an optical compensation sheet for an STN mode liquid crystal cell is described in JP-A-9-26572. A VA mode liquid crystal cell optical compensation sheet is described in Japanese Patent No. 2866372.
[0005]
In manufacturing a liquid crystal display device, components such as a liquid crystal cell, a polarizing plate, and an optical compensation sheet are sequentially attached with an adhesive. The liquid crystal cell, the polarizing plate, and the optical compensation sheet need to strictly adjust their optical directions (polarization axis and slow axis) corresponding to the display mode of the liquid crystal cell. For this reason, it is inevitable that a defective product whose sticking direction is out of specification is slightly generated. It is desirable to reuse those defective products by removing the parts.
However, when the optical compensation sheet is peeled off from the liquid crystal cell, there arises a problem that the optical compensation sheet is destroyed and cannot be reused. The liquid crystal cell to which a part of the optical compensation sheet is attached also needs a cleaning operation to remove a part of the attached optical compensation sheet in order to reuse it.
[0006]
Therefore, there is a demand for means for improving the strength without adversely affecting the optical function of the optical compensation sheet.
JP-A-8-27284 discloses a method for obtaining a high-strength optical compensation sheet by introducing a polymerizable group into a discotic liquid crystalline molecule, aligning the discotic liquid crystalline molecule, and then polymerizing the molecule. Has been.
In JP-A-9-152509, in addition to the discotic liquid crystalline molecules, a polymerizable group is also introduced into the polymer of the alignment film provided between the transparent support and the optically anisotropic layer. A method of copolymerizing tick liquid crystalline molecules is disclosed.
Japanese Patent Application Laid-Open No. 2000-235117 discloses an optical compensation sheet in which a transparent support and an optically anisotropic layer are bonded with a strength at which the peel strength is 400 g / cm or more. As means for enhancing the peel strength, a method of adding inorganic fine particles to a transparent support, an alignment film or an optically anisotropic layer is disclosed.
[0007]
[Problems to be solved by the invention]
By adopting the means described in JP-A-8-27284, JP-A-9-152509 and JP-A-2000-235117, an optical compensation sheet having excellent strength can be obtained.
However, when the present inventor further researched, even when adopting the improvement means of the conventional technique, when the optical compensation sheet is peeled off from the liquid crystal cell and reused, about once every several times or several tens of times, There was a problem that a part of the optical compensation sheet adhered to the substrate of the liquid crystal cell. Therefore, in order to peel off the optical compensation sheet from the liquid crystal cell and reuse it, it is necessary to further improve the strength of the optical compensation sheet.
An object of the present invention is to provide an optical compensation sheet having further improved strength.
Another object of the present invention is to provide an optical compensation sheet that can reuse components even if a defective product is produced in a bonding step during the manufacture of a liquid crystal display device.
[0008]
[Means for Solving the Problems]
The object of the present invention has been achieved by the following optical compensation sheets (1) to (11).
(1) An optical compensation sheet having an optically anisotropic layer formed from liquid crystalline molecules and a transparent support, wherein the optically anisotropic layer further has four or more double bonds in the molecule. An optical compensation sheet comprising a polymer of:
[0009]
(2) The optical compensation sheet according to (1), wherein the polyfunctional monomer is an ester of a polyol having 4 or more hydroxyl groups in the molecule and acrylic acid or methacrylic acid.
(3) The optical compensation sheet according to (1), wherein the liquid crystalline molecule is a discotic liquid crystalline molecule.
(4) The optical compensation sheet according to (3), wherein the discotic liquid crystalline molecule has a double bond, and the discotic liquid crystalline molecule and the polyfunctional monomer are copolymerized.
[0010]
(5) The optical compensation sheet according to (1), wherein an alignment film is provided between the optically anisotropic layer and the transparent support.
(6) The optical compensation sheet according to (5), wherein the alignment film is made of a polymer having a double bond in the side chain, and the alignment film polymer and the polyfunctional monomer are copolymerized.
(7) The optical compensation sheet according to (1), wherein the transparent support has a Re retardation value of 0 to 50 nm and an Rth retardation value of 70 to 400 nm.
[0011]
(8) The optical compensation sheet according to (1), wherein the transparent support comprises a cellulose acetate film having an acetylation degree of 59.0 to 61.5%.
(9) The optical compensation sheet according to (8), wherein the cellulose acetate film contains 0.01 to 20 parts by mass of an aromatic compound having at least two aromatic rings with respect to 100 parts by mass of cellulose acetate.
(10) The optical compensation sheet according to (8), wherein the cellulose acetate film is formed by a co-casting method.
(11) A cellulose acetate film was formed from a cellulose acetate solution using an ether having 2 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, or an ester having 2 to 12 carbon atoms as a solvent ( The optical compensation sheet according to 8).
(12) A liquid crystal display device comprising a liquid crystal cell and two polarizing plates disposed on both sides thereof, wherein at least one optical compensation sheet is disposed between the liquid crystal cell and at least one polarizing plate. The optical compensation sheet has an optically anisotropic layer formed from liquid crystalline molecules and a transparent support, and the transparent support may function as a transparent protective film of the polarizing plate, A liquid crystal display device comprising a polymer of a polyfunctional monomer having four or more double bonds in a molecule.
[0012]
【The invention's effect】
As a result of the inventor's research, it has been found that in order to further improve the strength of the optical compensation sheet, it is necessary to increase the number of double bonds that function as polymerizable functional groups in the optically anisotropic layer.
As described in JP-A-8-27284, a method of introducing a polymerizable group into liquid crystal molecules contained in an optically anisotropic layer is very effective for improving the strength. However, there is a limit to the number of polymerizable groups that can be introduced into the liquid crystal molecule. The molecular structure and the amount of liquid crystal molecules must be determined with priority given to the most important optical properties, and only the strength of the optically anisotropic layer cannot be considered.
The method for introducing a polymerizable group into the polymer of the alignment film described in JP-A-9-152509 is effective only at the interface between the alignment film and the optically anisotropic layer. In other words, the strength of the optically anisotropic layer itself cannot be improved. In particular, in an optical compensation sheet having a relatively thick optically anisotropic layer (for example, 1.5 μm or more), it is necessary to improve the strength of the optically anisotropic layer by using another means in combination.
The inorganic fine particles described in JP-A-2000-235117 are also effective for improving the strength of the optical compensation sheet. However, it is necessary to adjust the amount of inorganic fine particles used within a range that does not impair the functions of the optically anisotropic layer and the alignment film.
[0013]
As a result of further research, the present inventor added a polyfunctional monomer having four or more double bonds in the molecule to the optically anisotropic layer to form a polymer from the monomer, thereby significantly increasing the strength. We have succeeded in obtaining an improved optical compensation sheet. The polyfunctional monomer can remarkably increase the number of double bonds functioning as a polymerizable functional group in the optically anisotropic layer with little influence on the optical function of the optically anisotropic layer.
By performing the polymerization reaction after significantly increasing the number of double bonds in the optically anisotropic layer, an optical compensation sheet in which the strength of the optically anisotropic layer was remarkably improved was obtained. As a result, even if the optical compensation sheet of the present invention is attached to the liquid crystal cell and then peeled off, the problem that a part of the optical compensation sheet adheres to the substrate of the liquid crystal cell is hardly recognized.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
[Basic configuration of liquid crystal display]
FIG. 1 is a schematic diagram showing a basic configuration of a transmissive liquid crystal display device.
The transmissive liquid crystal display device shown in FIG. 1 includes a transparent protective film (1a), a polarizing film (2a), a transparent protective film (3a), a transparent support (4a), an optically anisotropic film in this order from the backlight (BL) side. Layer (5a), lower substrate (6a) of liquid crystal cell, rod-like liquid crystalline molecule (7), upper substrate (6b) of liquid crystal cell, optical anisotropic layer (5b), transparent support (4b), transparent protection It consists of a film (3b), a polarizing film (2b), and a transparent protective film (1b).
The transparent protective film (1a) to the transparent protective film (3a) constitute the lower polarizing plate. The transparent support (4a) to the optically anisotropic layer (5a) constitute the lower optical compensation sheet. The optically anisotropic layer (5b) to the transparent support (4b) constitute the upper optical compensation sheet. The transparent protective film (3b) to the transparent protective film (1b) constitute the upper polarizing plate. The lower polarizing plate and the lower optical compensation sheet may be integrated by combining the transparent protective film (3a) and the transparent support (4a) with a single polymer film. Similarly, the upper optical compensation sheet and the upper polarizing plate may be integrated by combining the transparent support (4b) and the transparent protective film (3b) with a single polymer film.
[0015]
FIG. 2 is a schematic diagram showing another basic configuration of the transmissive liquid crystal display device.
The transmissive liquid crystal display device shown in FIG. 2 includes a transparent protective film (1a), a polarizing film (2a), a transparent protective film (3a), a transparent support (4), and an optically anisotropic film in order from the backlight (BL) side. Layer (5), lower substrate (6a) of liquid crystal cell, rod-like liquid crystalline molecule (7), upper substrate (6b) of liquid crystal cell, transparent protective film (3b), polarizing film (2b), and transparent protective film (1b).
The transparent protective film (1a) to the transparent protective film (3a) constitute the lower polarizing plate. The transparent support (4) to the optically anisotropic layer (5) constitute an optical compensation sheet. The transparent protective film (3b) to the transparent protective film (1b) constitute the upper polarizing plate. The lower polarizing plate and the optical compensation sheet may be integrated by combining the transparent protective film (3a) and the transparent support (4) with a single polymer film.
[0016]
FIG. 3 is a schematic diagram showing still another basic configuration of the transmissive liquid crystal display device. The transmissive liquid crystal display device shown in FIG. 3 includes a transparent protective film (1a), a polarizing film (2a), a transparent protective film (3a), a lower substrate (6a) of a liquid crystal cell, and a rod shape in order from the backlight (BL) side Liquid crystalline molecule (7), upper substrate (6b) of liquid crystal cell, optical anisotropic layer (5), transparent support (4), transparent protective film (3b), polarizing film (2b), and transparent protective film (1b).
The transparent protective film (1a) to the transparent protective film (3a) constitute the lower polarizing plate. The optically anisotropic layer (5) to the transparent support (4) constitute an optical compensation sheet. The transparent protective film (3b) to the transparent protective film (1b) constitute the upper polarizing plate. The optical compensation sheet and the upper polarizing plate may be integrated by combining the transparent support (4) and the transparent protective film (3b) with a single polymer film.
[0017]
FIG. 4 is a schematic diagram showing a basic configuration of a reflective liquid crystal display device.
The reflective liquid crystal display device shown in FIG. 4 has a liquid crystal cell lower substrate (6a), rod-like liquid crystal molecules (7), liquid crystal cell upper substrate (6b), optically anisotropic in order from the reflector (RP) side. The protective layer (5), the transparent support (4), the transparent protective film (3), the polarizing film (2), and the transparent protective film (1).
The optically anisotropic layer (5) to the transparent support (4) constitute an optical compensation sheet. The transparent protective film (3) to the transparent protective film (1) constitute a polarizing plate. The optical compensation sheet and the polarizing plate may be integrated by combining the transparent support (4) and the transparent protective film (3) with a single polymer film.
[0018]
[Multifunctional monomer]
In the present invention, a polyfunctional monomer having 4 or more double bonds in the molecule is used. The double bond is preferably an ethylenic (aliphatic) unsaturated double bond. The number of double bonds in the molecule is preferably 4 to 20, more preferably 5 to 15, and most preferably 6 to 10.
The polyfunctional monomer is preferably an ester of an unsaturated fatty acid with a polyol having 4 or more hydroxyl groups in the molecule. Examples of unsaturated fatty acids include acrylic acid, methacrylic acid, maleic acid and itaconic acid. Acrylic acid and methacrylic acid are preferred.
The polyol having 4 or more hydroxyl groups in the molecule is preferably a tetrahydric or higher alcohol or a trihydric or higher alcohol oligomer. The oligomer has a molecular structure in which polyhydric alcohols are linked by an ether bond, an ester bond or a urethane bond. Oligomers having a molecular structure in which polyhydric alcohols are linked by ether bonds are preferred.
[0019]
Esters of polyol and (meth) acrylic acid include pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, polyether polyol poly (meth) acrylate, Poly (meth) acrylates of polyester polyols and poly (meth) acrylates of polyurethane polyols are included.
A commercial product of a polyfunctional monomer may be used. Monomers composed of an ester of polyol and acrylic acid are Mitsubishi Rayon Co., Ltd. (trade name: Diabeam UK-4154), Toa Gosei Co., Ltd. (trade name: Aronix M450) and Nippon Kayaku Co., Ltd. (trade name). : KYARAD · DPHA, SR355).
Two or more kinds of polyfunctional monomers may be used in combination.
[0020]
You may use together the polyfunctional monomer which has a 4 or more double bond in a molecule | numerator, and the monomer which has 1-3 double bonds in a molecule | numerator. The combined use of monomers is effective for adjusting the viscosity and strength. That is, as the number of double bonds in the monomer increases, the intermolecular interaction increases and the viscosity increases. When the viscosity increases, it takes time to align the liquid crystal compound. On the other hand, the greater the number of double bonds, the stronger the strength of the optical compensation sheet. Appropriate viscosity and appropriate strength can be easily achieved by using two or more types of monomers in combination.
The polyfunctional monomer having 4 or more double bonds in the molecule is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, based on the total amount of monomers.
The polyfunctional monomer is added to the optically anisotropic layer together with the liquid crystalline molecules. The addition amount of the polyfunctional monomer is preferably 0.1 to 50% by mass, and more preferably 1 to 20% by mass with respect to the liquid crystal molecules.
[0021]
[Transparent support]
That the support is transparent means that the light transmittance is 80% or more.
The transparent support preferably has a Re retardation value of 0 to 50 nm and an Rth retardation value of 70 to 400 nm. The Re retardation value and the Rth retardation value are defined by the following formulas (I) and (II), respectively.
(I) Re = (nx−ny) × d
(II) Rth = {(nx + ny) / 2−nz} × d
[0022]
In the formulas (I) and (II), nx is the refractive index in the slow axis direction (direction in which the refractive index is maximum) in the plane of the transparent support.
In the formulas (I) and (II), ny is the refractive index in the fast axis direction (direction in which the refractive index is minimized) in the plane of the transparent support.
In the formula (II), nz is a refractive index in the thickness direction.
In the formulas (I) and (II), d is the thickness of the transparent support whose unit is nm.
[0023]
When two optical compensation sheets are used in the liquid crystal display device, the Rth retardation value of the transparent support is preferably 70 to 200 nm.
When one optical compensation sheet is used in the liquid crystal display device, the Rth retardation value of the transparent support is preferably 150 to 400 nm.
In addition, it is preferable that the birefringence ((DELTA) n: nx-ny) of a transparent support body is less than 0.002. The birefringence {(nx + ny) / 2−nz} in the thickness direction of the transparent support is preferably 0.001 to 0.04.
[0024]
The transparent support is preferably formed from a polymer film. As the polymer for forming the polymer film, cellulose ester is preferable, cellulose acetate is more preferable, and cellulose acetate having an acetylation degree of 59.0 to 61.5% is more preferable. The degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation follows the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).
The polymer forming the film has a viscosity average degree of polymerization (DP) of preferably 250 or more, and more preferably 290 or more. The polymer preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a mass average molecular weight, Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.0 to 1.7, more preferably 1.3 to 1.65, and most preferably 1.4 to 1.6. preferable.
[0025]
In order to adjust the retardation of the polymer film, an aromatic compound having at least two aromatic rings can be used as a retardation increasing agent.
When a cellulose acetate film is used as the polymer film, the aromatic compound is used in the range of 0.01 to 20 parts by mass with respect to 100 parts by mass of the cellulose acetate. The aromatic compound is preferably used in the range of 0.05 to 15 parts by mass, more preferably in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of cellulose acetate. Two or more aromatic compounds may be used in combination.
The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.
[0026]
The aromatic hydrocarbon ring is particularly preferably a 6-membered ring (that is, a benzene ring).
The aromatic heterocycle is generally an unsaturated heterocycle. The aromatic heterocycle is preferably a 5-membered ring, 6-membered ring or 7-membered ring, more preferably a 5-membered ring or 6-membered ring. Aromatic heterocycles generally have the most double bonds. As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of aromatic heterocycles include furan ring, thiophene ring, pyrrole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring, pyridine ring , Pyridazine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring.
As the aromatic ring, benzene ring, furan ring, thiophene ring, pyrrole ring, oxazole ring, thiazole ring, imidazole ring, triazole ring, pyridine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring are preferable, More preferred are a benzene ring and a 1,3,5-triazine ring.
It is particularly preferred that the aromatic compound has at least one 1,3,5-triazine ring.
[0027]
The number of aromatic rings contained in the aromatic compound is preferably 2 to 20, more preferably 2 to 12, still more preferably 2 to 8, and most preferably 2 to 6. .
The bonding relationship between two aromatic rings can be classified into (a) when a condensed ring is formed, (b) when directly linked by a single bond, and (c) when linked via a linking group (for aromatic rings). , Spiro bonds cannot be formed). The connection relationship may be any of (a) to (c).
[0028]
Examples of the condensed ring of (a) (condensed ring of two or more aromatic rings) include an indene ring, a naphthalene ring, an azulene ring, a fluorene ring, a phenanthrene ring, an anthracene ring, an acenaphthylene ring, a naphthacene ring, a pyrene ring, Indole ring, isoindole ring, benzofuran ring, benzothiophene ring, indolizine ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring, purine ring, indazole ring, chromene ring, quinoline ring, isoquinoline ring, quinolidine Ring, quinazoline ring, cinnoline ring, quinoxaline ring, phthalazine ring, pteridine ring, carbazole ring, acridine ring, phenanthridine ring, xanthene ring, phenazine ring, phenothiazine ring, phenoxathiin ring, phenoxazine ring and thianthrene ring BeNaphthalene ring, azulene ring, indole ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring and quinoline ring are preferred.
The single bond (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be bonded with two or more single bonds to form an aliphatic ring or a non-aromatic heterocyclic ring between the two aromatic rings.
[0029]
The linking group in (c) is also preferably bonded to carbon atoms of two aromatic rings. The linking group is preferably an alkylene group, an alkenylene group, an alkynylene group, —CO—, —O—, —NH—, —S—, or a combination thereof. Examples of linking groups composed of combinations are shown below. In addition, the relationship between the left and right in the following examples of the linking group may be reversed.
c1: -CO-O-
c2: —CO—NH—
c3: -alkylene-O-
c4: —NH—CO—NH—
c5: —NH—CO—O—
c6: —O—CO—O—
c7: -O-alkylene-O-
c8: -CO-alkenylene-
c9: -CO-alkenylene-NH-
c10: -CO-alkenylene-O-
c11: -alkylene-CO-O-alkylene-O-CO-alkylene-
c12: -O-alkylene-CO-O-alkylene-O-CO-alkylene-O-
c13: -O-CO-alkylene-CO-O-
c14: -NH-CO-alkenylene-
c15: -O-CO-alkenylene-
[0030]
The aromatic ring and the linking group may have a substituent.
Examples of the substituent include halogen atom (F, Cl, Br, I), hydroxyl, carboxyl, cyano, amino, nitro, sulfo, carbamoyl, sulfamoyl, ureido, alkyl group, alkenyl group, alkynyl group, aliphatic acyl group , Aliphatic acyloxy group, alkoxy group, alkoxycarbonyl group, alkoxycarbonylamino group, alkylthio group, alkylsulfonyl group, aliphatic amide group, aliphatic sulfonamido group, aliphatic substituted amino group, aliphatic substituted carbamoyl group, aliphatic Substituted sulfamoyl groups, aliphatic substituted ureido groups and non-aromatic heterocyclic groups are included.
[0031]
The alkyl group preferably has 1 to 8 carbon atoms. A chain alkyl group is preferable to a cyclic alkyl group, and a linear alkyl group is particularly preferable. The alkyl group may further have a substituent (eg, hydroxy, carboxy, alkoxy group, alkyl-substituted amino group). Examples of alkyl groups (including substituted alkyl groups) include methyl, ethyl, n-butyl, n-hexyl, 2-hydroxyethyl, 4-carboxybutyl, 2-methoxyethyl and 2-diethylaminoethyl.
The alkenyl group preferably has 2 to 8 carbon atoms. A chain alkenyl group is preferable to a cyclic alkenyl group, and a linear alkenyl group is particularly preferable. The alkenyl group may further have a substituent. Examples of alkenyl groups include vinyl, allyl and 1-hexenyl.
The alkynyl group preferably has 2 to 8 carbon atoms. A chain alkynyl group is preferable to a cyclic alkynyl group, and a linear alkynyl group is particularly preferable. The alkynyl group may further have a substituent. Examples of alkynyl groups include ethynyl, 1-butynyl and 1-hexynyl.
[0032]
The aliphatic acyl group preferably has 1 to 10 carbon atoms. Examples of the aliphatic acyl group include acetyl, propanoyl and butanoyl.
The aliphatic acyloxy group preferably has 1 to 10 carbon atoms. Examples of the aliphatic acyloxy group include acetoxy.
The number of carbon atoms of the alkoxy group is preferably 1 to 8. The alkoxy group may further have a substituent (eg, alkoxy group). Examples of alkoxy groups (including substituted alkoxy groups) include methoxy, ethoxy, butoxy and methoxyethoxy.
The alkoxycarbonyl group preferably has 2 to 10 carbon atoms. Examples of the alkoxycarbonyl group include methoxycarbonyl and ethoxycarbonyl.
The number of carbon atoms of the alkoxycarbonylamino group is preferably 2 to 10. Examples of the alkoxycarbonylamino group include methoxycarbonylamino and ethoxycarbonylamino.
[0033]
The alkylthio group preferably has 1 to 12 carbon atoms. Examples of the alkylthio group include methylthio, ethylthio and octylthio.
The alkylsulfonyl group preferably has 1 to 8 carbon atoms. Examples of the alkylsulfonyl group include methanesulfonyl and ethanesulfonyl.
The aliphatic amide group preferably has 1 to 10 carbon atoms. Examples of the aliphatic amide group include acetamide.
The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamido group include methanesulfonamido, butanesulfonamido and n-octanesulfonamido.
The number of carbon atoms of the aliphatic substituted amino group is preferably 1 to 10. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino.
The aliphatic substituted carbamoyl group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl.
The aliphatic substituted sulfamoyl group preferably has 1 to 8 carbon atoms. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl.
The number of carbon atoms in the aliphatic substituted ureido group is preferably 2 to 10. Examples of the aliphatic substituted ureido group include methylureido.
Examples of non-aromatic heterocyclic groups include piperidino and morpholino.
The molecular weight of the retardation increasing agent is preferably 300 to 800.
Examples of retardation increasing compounds are described in JP-A Nos. 2000-1111014 and 2000-275434 and WO00 / 65384.
[0034]
It is preferable to produce a polymer film by a solvent casting method. In the solvent cast method, a film is produced using a solution (dope) in which a polymer is dissolved in an organic solvent.
The organic solvent is a solvent selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to contain.
The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.
[0035]
Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole.
Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.
Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.
The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogenated hydrocarbon hydrogen atoms substituted with halogen is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is 40 to 60 mol%, and most preferably. Methylene chloride is a representative halogenated hydrocarbon.
Two or more organic solvents may be mixed and used.
[0036]
A polymer solution can be prepared by a general method. The general method means that the treatment is performed at a temperature of 0 ° C. or higher (room temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a normal solvent cast method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly methylene chloride) as the organic solvent.
The amount of the polymer is adjusted so that it is contained in an amount of 10 to 40% by mass in the resulting solution. The amount of polymer is more preferably 10 to 30% by mass. Arbitrary additives described later may be added to the organic solvent (main solvent).
The solution can be prepared by stirring the polymer and the organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, the polymer and the organic solvent are put in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., more preferably 80 to 110 ° C.
[0037]
Each component may be coarsely mixed in advance and then placed in a container. Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. The container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure.
When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid.
It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall.
Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in the container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like.
[0038]
A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, the polymer can be dissolved in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can melt | dissolve a polymer with a normal melt | dissolution method, there exists an effect that a uniform solution can be obtained rapidly according to a cooling melt | dissolution method.
In the cooling dissolution method, first, a polymer is gradually added to an organic solvent with stirring at room temperature.
The amount of the polymer is preferably adjusted so as to be contained in the mixture by 10 to 40% by mass. The amount of polymer is more preferably 10 to 30% by mass. Furthermore, you may add the arbitrary additive mentioned later in a mixture.
[0039]
The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). Upon cooling in this way, the mixture of polymer and organic solvent solidifies.
The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling until the final cooling temperature is reached.
[0040]
Further, when this is heated to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.), the polymer dissolves in the organic solvent. The temperature can be raised by simply leaving it at room temperature or in a warm bath.
The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is a value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. .
A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether or not the dissolution is sufficient can be determined by merely observing the appearance of the solution with the naked eye.
[0041]
In the cooling dissolution method, it is desirable to use a sealed container in order to avoid moisture mixing due to condensation during cooling. In the cooling and heating operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container.
In addition, according to differential scanning calorimetry (DSC), a 20 mass% solution obtained by dissolving cellulose acetate (acetylation degree: 60.9%, viscosity average polymerization degree: 299) in methyl acetate by a cooling dissolution method was 33. There exists a quasi-phase transition point between a sol state and a gel state in the vicinity of ° C., and a uniform gel state is obtained below this temperature. Therefore, this solution needs to be stored at a temperature equal to or higher than the pseudo phase transition temperature, preferably about the gel phase transition temperature plus about 10 ° C. However, this pseudo phase transition temperature varies depending on the degree of acetylation of cellulose acetate, the degree of viscosity average polymerization, the concentration of the solution, and the organic solvent used.
[0042]
A polymer film is produced from the prepared polymer solution (dope) by a solvent cast method. Moreover, it is preferable to add the above-mentioned retardation increasing agent to the dope.
The dope is cast on a drum or band, and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is 18 to 35%. The surface of the drum or band is preferably finished in a mirror state. Regarding casting and drying methods in the solvent cast method, U.S. Pat. Nos. 2,336,310, 2,367,603, 2,429,078, 2,429,297, 2,429,978, 2,607,704, 2,739,69, U.S. 2,739,070, British Patent 6,407,331, No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.
The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried by high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.
[0043]
Two or more layers can be cast at the same time (co-cast) using the prepared polymer solution (dope) to form a film. The concentration of the dope before co-casting is preferably adjusted so that the solid content is 10 to 50%.
When co-casting a plurality of cellulose acetate solutions, it is possible to produce a film while casting and laminating a solution containing cellulose acetate from a plurality of casting openings provided at intervals in the traveling direction of the support. it can. The co-casting is described in JP-A Nos. 61-158414, 1-122419, and 11-198285. A film may be produced by casting a cellulose acetate solution from two casting ports (Japanese Patent Publication Nos. 60-27562, 61-94724, 61-947245, 61-104413). No. 61-158413 and JP-A-6-134933).
Also, a method of casting a cellulose acetate film in which a flow of a high-viscosity cellulose acetate solution is wrapped with a low-viscosity cellulose acetate solution and the high- and low-viscosity cellulose acetate solution is simultaneously extruded (described in JP-A-56-162617) Is also applicable.
Furthermore, using two casting ports, the film cast on the support is peeled off by the first casting port, and the second casting is performed on the side that is in contact with the support surface to produce a film (special Japanese Patent Publication No. 44-20235).
The plurality of dopes co-casting may have the same composition. In addition to the polymer film used as the transparent support, other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, an ultraviolet absorbing layer, and a polarizing layer) can be cast simultaneously.
[0044]
In the single layer casting, in order to obtain a certain film thickness, it is necessary to extrude a dope having a high concentration and a high viscosity. Therefore, the stability of the dope is poor, and solid matter is generated, which may cause a failure or a problem of poor flatness. When a plurality of dopes are co-cast from a plurality of casting ports, a highly viscous solution can be simultaneously extruded onto the support. As a result, an excellent planar film with good flatness can be produced. Further, by using a thick dope, dry addition is reduced and the film production rate is increased.
[0045]
A plasticizer can be added to the polymer film in order to improve mechanical properties or to increase the drying speed. As the plasticizer, phosphoric acid ester or carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred.
The addition amount of the plasticizer is preferably 0.1 to 25% by mass, more preferably 1 to 20% by mass, and most preferably 3 to 15% by mass of the amount of the polymer.
[0046]
A degradation inhibitor (eg, antioxidant, peroxide decomposer, radical inhibitor, metal deactivator, acid scavenger, amine) may be added to the polymer film. The deterioration preventing agents are described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The addition amount of the deterioration preventing agent is preferably 0.01 to 1% by mass of the solution (dope) to be prepared, and more preferably 0.01 to 0.2% by mass. When the addition amount is less than 0.01% by mass, the effect of the deterioration preventing agent is hardly recognized. When the added amount exceeds 1% by mass, bleeding-out (bleeding) of the deterioration preventing agent to the film surface may be observed. Examples of particularly preferred deterioration inhibitors include butylated hydroxytoluene (BHT) and tribenzylamine (TBA).
[0047]
Various high thermal conductivity particles can be added to the polymer film in order to improve the thermal conductivity of the transparent support. The high heat conductive fine particles are preferably formed from a transparent material. Specific examples of materials include aluminum nitride, silicon nitride, boron nitride, magnesium nitride, silicon carbide, aluminum oxide, silicon oxide, zinc oxide, magnesium oxide, carbon (including diamond) and metals. The average particle size of the high thermal conductivity particles is preferably 0.05 to 80 μm, and more preferably 0.1 to 10 μm.
High thermal conductivity particles are preferably used in the range of 5 to 100 parts by mass, more preferably in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the polymer.
[0048]
The polymer film is preferably stretched to reduce the hygroscopic expansion (decrease the hygroscopic expansion coefficient). When reducing hygroscopic expansion by stretching, it is desirable to uniformly prevent distortion in all directions in the plane. For that purpose, it is preferable to carry out a biaxial stretching treatment.
Biaxial stretching includes simultaneous biaxial stretching and sequential biaxial stretching. From the viewpoint of continuous production, a sequential biaxial stretching method is preferred. In the sequential biaxial stretching method, after the dope is cast, the polymer film is peeled off from the band or drum, stretched in the width direction (direction perpendicular to the casting direction), and then stretched in the longitudinal direction. The order in which the stretching is performed twice in the width direction and the longitudinal direction may be reversed.
The stretching in the width direction is described in JP-A-62-115035, JP-A-4-152125, JP-A-4284221, JP-A-4-298310, and JP-A-11-48271. The film is stretched at room temperature or under heating conditions. The heating temperature is preferably not higher than the glass transition temperature of the film. The film can be stretched during the drying process during manufacture. It is preferable to stretch in a state where the solvent remains in the film. In the case of stretching in the longitudinal direction, for example, the film is stretched by adjusting the speed of the film transport roller so that the film winding speed is higher than the film stripping speed. In the case of stretching in the width direction, the film can be stretched by conveying the film while holding the film with a tenter and gradually widening the tenter. After the film is dried, it can be stretched using a stretching machine (preferably uniaxial stretching using a long stretching machine). The film draw ratio (the ratio of the increase due to stretching to the original length) is preferably 5 to 50%, more preferably 10 to 40%, and most preferably 15 to 35%.
[0049]
The steps from casting to drying may be performed in an atmosphere of a relatively inert gas (eg, nitrogen gas). As the polymer film winder, a commonly used apparatus can be used. As a winding method, a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress can be employed.
By carrying out biaxial stretching as described above, the hygroscopic expansion coefficient of the film can be reduced. The hygroscopic expansion coefficient is the amount of change in the length of the sample when the relative humidity is changed at a constant temperature.
In order to prevent a frame-like transmittance increase, the hygroscopic expansion coefficient of the cellulose acetate film is 30 × 10^-Five/% RH or less, preferably 15 × 10^-Five/% RH or less is more preferable, 10 × 10^-Five/% RH or less is most preferable. The hygroscopic expansion coefficient is preferably small, but usually 1.0 × 10^-Five/% RH or more.
[0050]
First, the hygroscopic expansion coefficient is 5 mm wide from the produced polymer film. A sample with a length of 20 mm was cut out, one end was fixed and 25 ° C, 20% RH (R₀) Hanging a weight of 0.5g on the other end and letting it stand for 10 minutes length (L₀). Next, the temperature remains at 25 ° C. and the humidity is 80% RH (R₁) And length (L₁). The hygroscopic expansion coefficient is calculated by the following equation. The measurement is performed 10 samples for the same sample, and the average value is adopted.
Hygroscopic expansion coefficient [/% RH] = {(L₁-L₀) / L₀} / (R₁-R₀)
[0051]
The dimensional change due to moisture absorption may be achieved by reducing the free volume in the polymer film. It is the amount of residual solvent at the time of film formation that greatly influences the free volume.
A common technique for reducing residual solvent is to dry at high temperature and for a long time. However, if it is dried for a long time, it naturally reduces productivity. Therefore, the amount of residual solvent in the polymer film is preferably in the range of 0.01 to 1% by mass, more preferably in the range of 0.02 to 0.07% by mass, and 0.03 to 0.05%. Most preferably, it is in the range of mass%.
By controlling the amount of the residual solvent, the polymer film can be produced at low cost with high productivity.
[0052]
As another method for reducing the dimensional change due to moisture absorption, it is preferable to add a compound having a hydrophobic group. As the hydrophobic group, an alkyl group and phenyl are preferable. The compound to be used is preferably selected from plasticizers and deterioration inhibitors that can be added to the polymer film. Specific compound examples include triphenyl phosphate (TPP) and tribenzylamine (TBA).
The addition amount of the compound having a hydrophobic group is preferably in the range of 0.01 to 10% by mass of the polymer solution (dope), more preferably in the range of 0.1 to 5% by mass. The most preferable range is 3% by mass.
[0053]
The polymer film is preferably subjected to a surface treatment. Surface treatment includes corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment and ultraviolet irradiation treatment. An undercoat layer (described in JP-A-7-333433) may be provided instead of or in addition to the surface treatment.
The surface energy of the film after the surface treatment is preferably 55 mN / m or more, and more preferably 60 mN / m or more and 75 mN / m or less.
From the viewpoint of maintaining the flatness of the film, the temperature of the polymer film in the surface treatment is preferably not higher than the Tg (glass transition temperature) of the polymer, and specifically not higher than 150 ° C.
When the polymer film is a cellulose acetate film, the surface treatment is preferably an acid treatment or an alkali treatment, that is, a saponification treatment for cellulose acetate, and more preferably an alkali saponification treatment.
[0054]
The alkali saponification treatment can be performed in a cycle in which the film surface is immersed in an alkali solution, then washed with water and dried. You may neutralize with an acidic solution before washing with water. Examples of the alkaline solution include a potassium hydroxide solution and a sodium hydroxide solution, and the prescribed concentration of hydroxide ions is preferably in the range of 0.1 to 3.0N, and in the range of 0.5 to 2.0N. More preferably. The alkaline solution temperature is preferably in the range of room temperature to 90 ° C, and more preferably in the range of 40 to 70 ° C.
In order to efficiently perform the alkali saponification treatment, it is also preferable to perform a saponification treatment in which an alkali solution is applied to the cellulose acetate film. After the saponification treatment, it is preferable to remove alkali from the film surface by washing with water. In the case of saponification treatment by coating, the alkali solution preferably has good wettability with respect to the cellulose acetate film. The wettability of the coating solution is mainly determined by the type of solvent. As the solvent having good wettability, alcohol (eg, isopropyl alcohol, n-butanol, methanol, ethanol) is representative. As an auxiliary solvent, it is preferable to further add water or glycol (eg, propylene glycol, ethylene glycol).
The surface energy of a solid can be determined by a contact angle method, a wet heat method, and an adsorption method as described in “Basics and Applications of Wetting” (issued by Realize 1989.12.10). In the case of cellulose acetate film, the contact angle method is preferably used.
Specifically, two types of solutions having known surface energies are dropped on a cellulose acetate film, and at the intersection of the surface of the droplet and the surface of the film, the angle formed by the tangent line drawn on the droplet and the surface of the film The surface angle of the film can be calculated by defining the angle containing the droplet as the contact angle.
[0055]
[Alignment film]
The alignment film has a function of defining the alignment direction of the liquid crystalline molecules. The alignment film is an organic compound (eg, ω-tricosanoic acid) formed by rubbing treatment of an organic compound (preferably polymer), oblique deposition of an inorganic compound, formation of a layer having a microgroove, or Langmuir-Blodgett method (LB film). , Dioctadecylmethylammonium chloride, methyl stearylate). Furthermore, an alignment film in which an alignment function is generated by application of an electric field, application of a magnetic field, or light irradiation is also known.
[0056]
The alignment film is preferably formed by polymer rubbing treatment. In principle, the polymer used for the alignment film has a molecular structure having a function of aligning liquid crystal molecules.
In the present invention, in addition to the function of aligning liquid crystalline molecules, a cross-linking having a function of aligning a side chain having a crosslinkable functional group (eg, double bond) to the main chain or aligning liquid crystalline molecules. It is preferable to introduce a functional functional group into the side chain.
As the main chain of the alignment film polymer, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polyacrylic acid ester, polymethacrylic acid ester (eg, polymethyl methacrylate), polyacrylamide (eg, poly (N-methylolacrylamide)) , Polymethacrylamide, polyolefin (eg, polystyrene, polyvinyl toluene, polyethylene, polypropylene), chlorinated polyolefin (eg, chlorosulfonated polyethylene, polyvinyl chloride), cellulose ester (eg, cellulose nitrate), polyester (eg, polycarbonate) ), Polyimide, polyamide (eg, polyamic acid), polyvinyl ester (eg, polyvinyl acetate) or cellulose ether (eg, carboxymethyl cellulose).Copolymer composed of two or more kinds of repeating units (eg, acrylic acid / methacrylic acid copolymer, styrene / maleimide copolymer, styrene / vinyl toluene copolymer, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate) Copolymers) may be used. A reaction product of a silane coupling agent can also be used as the alignment film polymer.
[0057]
As the main chain of the alignment film polymer, poly (N-methylolacrylamide), carboxymethylcellulose, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polyimide and polyamide are preferable, and polyvinyl alcohol is particularly preferable.
The saponification degree of polyvinyl alcohol is preferably 70 to 100%, more preferably 80 to 100%, and most preferably 85 to 95%. The degree of polymerization of polyvinyl alcohol is preferably 100 to 3000.
A side chain having a function of aligning liquid crystal molecules generally has a hydrophobic group as a functional group. The specific type of functional group is determined according to the type of liquid crystal molecule and the required alignment state.
[0058]
When a side chain having a crosslinkable functional group is bonded to the main chain of the alignment film polymer, or a crosslinkable functional group is introduced into a side chain having a function of aligning liquid crystalline molecules, the alignment film polymer and the optically anisotropic film The polyfunctional monomer contained in the conductive layer can be copolymerized. As a result, not only between the polyfunctional monomer and the polyfunctional monomer, but also between the alignment film polymer and the alignment film polymer and between the polyfunctional monomer and the alignment film polymer is firmly bonded by a covalent bond. Therefore, the strength of the optical compensation sheet can be remarkably improved by introducing the crosslinkable functional group into the alignment film polymer.
The crosslinkable functional group of the alignment film polymer preferably contains a double bond as in the case of the polyfunctional monomer. Below, the example of the crosslinkable functional group containing a double bond is shown.
[0059]
[Chemical 1]

[0060]
The crosslinkable functional group may be directly bonded to the main chain of the alignment film polymer or may be bonded via a linking group.
The linking group is preferably a divalent linking group selected from the group consisting of an alkylene group, an arylene group, -CO-, -NH-, -O-, -S-, and combinations thereof. The alkylene group preferably has 1 to 12 carbon atoms. The arylene group is preferably phenylene.
[0061]
The alignment film polymer (especially a polymer having polyvinyl alcohol as the main chain) can be cross-linked using a cross-linking agent separately from the cross-linkable functional group.
As the crosslinking agent, aldehydes, N-methylol compounds, dioxane derivatives, compounds that act by activating carboxyl groups, active vinyl compounds, active halogen compounds, isoxazoles and dialdehyde starch can be used. Examples of aldehydes include formaldehyde, glyoxal and glutaraldehyde. Examples of the N-methylol compound include dimethylol urea and methylol dimethylhydantoin. Examples of the dioxane derivative include 2,3-dihydroxydioxane. Examples of compounds that act by activating the carboxyl group include carbenium, 2-naphthalenesulfonate, 1,1-bispyrrolidino-1-chloropyridinium and 1-morpholinocarbonyl-3- (sulfonatoaminomethyl). It is. Examples of active vinyl compounds include 1,3,5-triacroyl-hexahydro-s-triazine, bis (vinylsulfone) methane and N, N′-methylenebis- [β- (vinylsulfonyl) propionamide]. Examples of the active halogen compound include 2,4-dichloro-6-hydroxy-S-triazine. Aldehydes are preferred, and glutaraldehyde is particularly preferred. Two or more kinds of crosslinking agents may be used in combination.
[0062]
The addition amount of the crosslinking agent is preferably in the range of 0.1 to 20% by mass of the polymer, and more preferably in the range of 0.5 to 15% by mass. The unreacted crosslinking agent remaining in the alignment film is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less of the alignment film.
In the formation of the alignment film, a coating solution containing the alignment film polymer is applied on the transparent support. As the solvent for the coating solution, an organic solvent (eg, methanol) or a mixed solvent of water and an organic solvent is preferable. As a coating method, a spin coating method, a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method, or an E-type coating method can be employed. The E type coating method is particularly preferred. The drying temperature of the coating film is preferably 20 to 110 ° C., more preferably 60 to 100 ° C., and most preferably in the range of 80 to 100 ° C. The drying time is preferably 1 minute to 36 hours, more preferably 5 to 30 minutes.
[0063]
The rubbing treatment can be performed by a known method. That is, the alignment function is obtained by rubbing the surface of the alignment film in a certain direction using paper, cloth (gauze, felt, nylon, polyester fiber) or rubber. In general, rubbing is performed several times using a cloth in which fibers having a uniform length and thickness are planted on average.
Next, the alignment film functions to align the liquid crystalline molecules of the optically anisotropic layer provided on the alignment film. Thereafter, as necessary, the alignment film polymer and the polyfunctional monomer contained in the optically anisotropic layer are reacted, or the alignment film polymer is crosslinked using a crosslinking agent.
The thickness of the alignment film is preferably in the range of 0.1 to 10 μm.
[0064]
[Optically anisotropic layer]
The optically anisotropic layer is formed from liquid crystal molecules. As the liquid crystal molecules, rod-like liquid crystal molecules or discotic liquid crystal molecules are preferably used.
Examples of rod-like liquid crystalline molecules include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines. , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used. The rod-like liquid crystalline molecule includes a metal complex.
For rod-like liquid crystalline molecules, quarterly review of chemical review, Vol. 22, Chemistry of Liquid Crystals (1994), Chapter 4, Chapter 7 and Chapter 11 of the Chemical Society of Japan, and Liquid Crystal Device Handbook, Japan Society for the Promotion of Science 142 Is described in Chapter 3.
Discotic liquid crystalline molecules are also described in various literature (C. Destrade et al., Mol. Crysr. Liq. Cryst., Vol. 71, page 111 (1981); Liquid Crystal Chemistry, Chapter 5, Chapter 10, Section 2 (1994); B. Kohne et al., Angew. Chem. Soc. Chem. Comm., Page 1794 (1985); J. Zhang et al., J Am. Chem. Soc., Vol. 116, page 2655 (1994)).
[0065]
The liquid crystal molecule preferably has a double bond as a polymerizable functional group. When a double bond is introduced into the liquid crystalline molecule as a polymerizable functional group, the polyfunctional monomer contained in the optically anisotropic layer and the liquid crystalline molecule can be copolymerized. As a result, not only between the polyfunctional monomer and the polyfunctional monomer, but also between the liquid crystal molecule and the liquid crystal molecule, and between the polyfunctional monomer and the liquid crystal molecule are firmly bonded by a covalent bond. Therefore, the strength of the optical compensation sheet can be remarkably improved by introducing the crosslinkable functional group into the liquid crystalline molecule.
[0066]
In a discotic liquid crystal molecule, when a polymerizable functional group is directly connected to a disc-shaped core, it becomes difficult to maintain the alignment state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable functional group. Accordingly, the discotic liquid crystalline molecule having a polymerizable functional group is preferably a compound represented by the following formula (I).
[0067]
(I) D (-LQ)_n
In formula (I), D is a discotic core; L is a divalent linking group; Q is a polymerizable functional group; and n is an integer from 4 to 12.
An example of the disk-shaped core (D) is shown below. In each of the following examples, LQ (or QL) means a combination of a divalent linking group (L) and a polymerizable group (Q).
[0068]
[Chemical 2]

[0069]
[Chemical Formula 3]

[0070]
[Formula 4]

[0071]
[Chemical formula 5]

[0072]
[Chemical 6]

[0073]
[Chemical 7]

[0074]
[Chemical 8]

[0075]
In the formula (I), the divalent linking group (L) is selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. A divalent linking group is preferred. The divalent linking group (L) is a divalent combination of at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO-, -NH-, -O-, and -S-. More preferably, it is a linking group. The divalent linking group (L) is most preferably a divalent linking group in which at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO- and -O- are combined. . The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The number of carbon atoms in the arylene group is preferably 6 to 10.
[0076]
Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is bonded to the polymerizable group (Q). AL represents an alkylene group or an alkenylene group, and AR represents an arylene group. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group).
L1: -AL-CO-O-AL-
L2: -AL-CO-O-AL-O-
L3: -AL-CO-O-AL-O-AL-
L4: -AL-CO-O-AL-O-CO-
L5: -CO-AR-O-AL-
L6: -CO-AR-O-AL-O-
L7: -CO-AR-O-AL-O-CO-
L8: -CO-NH-AL-
L9: -NH-AL-O-
L10: -NH-AL-O-CO-
[0077]
L11: -O-AL-
L12: -O-AL-O-
L13: -O-AL-O-CO-
L14: -O-AL-O-CO-NH-AL-
L15: -O-AL-S-AL-
L16: -O-CO-AR-O-AL-CO-
L17: -O-CO-AR-O-AL-O-CO-
L18: -O-CO-AR-O-AL-O-AL-O-CO-
L19: -O-CO-AR-O-AL-O-AL-O-AL-O-CO-
L20: -S-AL-
L21: -S-AL-O-
L22: -S-AL-O-CO-
L23: -S-AL-S-AL-
L24: -S-AR-AL-
[0078]
Examples of the polymerizable functional group (Q) of the formula (I) are the same as the examples (Q1 to Q6) of the polymerizable functional group described for the alignment film polymer.
In the formula (I), n is an integer of 4 to 12. A specific number is determined according to the type of the disk-shaped core (D). In addition, although the combination of several L and Q may differ, it is preferable that it is the same.
[0079]
The optically anisotropic layer can be formed by applying a liquid crystal molecule and, if necessary, a coating liquid containing a polymerizable initiator and optional components on the alignment film.
The thickness of the optically anisotropic layer is preferably 0.5 to 100 μm, and more preferably 0.5 to 30 μm.
[0080]
After forming the optically anisotropic layer, the polyfunctional monomer is polymerized. When the alignment film polymer or the liquid crystalline molecule has a polymerizable group, it is copolymerized with a polyfunctional monomer.
The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. A photopolymerization reaction is preferred.
Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin. Compound (described in US Pat. No. 2,722,512), polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US Pat. No. 3,549,367) Acridine and phenazine compounds (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,212,970).
The amount of the photopolymerization initiator used is preferably 0.01 to 20% by mass, more preferably 0.5 to 5% by mass, based on the solid content of the coating solution.
It is preferable to use ultraviolet rays for light irradiation for polymerization.
Irradiation energy is 20 to 5000 mJ / cm²Preferably, 100 to 800 mJ / cm²More preferably. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.
A protective layer may be provided on the optically anisotropic layer.
[0081]
[Polarizer]
A polarizing plate consists of a polarizing film and two transparent protective films arrange | positioned at the both sides. As the transparent protective film, a cellulose acetate film is generally used. As described above, the transparent support of the optical compensation sheet can be used as one protective film. In this case, the optical compensation sheet and the polarizing plate are integrated (usually functioning as an elliptically polarizing plate). In the integrated elliptically polarizing plate, the slow axis of the transparent support of the optical compensation sheet and the transmission axis of the polarizing film are arranged so as to be substantially parallel.
The moisture permeability of the transparent protective film is 100 to 1000 (g / m²) / 24 hrs, preferably 300 to 700 (g / m²) / 24 hrs.
Examples of the polarizing film include an iodine polarizing film, a dye polarizing film using a dichroic dye, and a polyene polarizing film. The iodine polarizing film and the dye polarizing film are generally manufactured using a polyvinyl alcohol film.
[0082]
[Liquid Crystal Display]
An optical compensation sheet or a polarizing plate having an optical compensation sheet is advantageously used in a liquid crystal display device, particularly a transmissive liquid crystal display device.
The transmissive liquid crystal display device includes a liquid crystal cell and two polarizing plates disposed on both sides thereof. The liquid crystal cell carries a liquid crystal between two electrode substrates.
When the optical compensation sheet is used in a liquid crystal display device, one optical compensation sheet according to the present invention is disposed between the liquid crystal cell and one polarizing plate, or the optical compensation sheet is disposed between the liquid crystal cell and both polarizing plates. Two optical compensation sheets according to the invention are arranged.
When the polarizing plate is used in a liquid crystal display device, a polarizing plate having an optical compensation sheet according to the present invention may be used as one of the two polarizing plates. Instead of both polarizing plates, a polarizing plate having an optical compensation sheet according to the present invention may be used. When the polarizing plate having the optical compensation sheet according to the present invention is used in a liquid crystal display device, the polarizing plate is disposed so that the optical compensation sheet used as the protective film is on the liquid crystal cell side.
[0083]
The liquid crystal cell is preferably in a TN mode, an ECB mode, a VA mode, or an OCB mode. The VA mode includes an MVA mode.
In a TN mode liquid crystal cell, rod-like liquid crystalline molecules are substantially horizontally aligned when no voltage is applied, and are twisted and aligned at 60 to 120 °.
The TN mode liquid crystal cell is most frequently used as a color TFT liquid crystal display device, and is described in many documents.
[0084]
In a VA mode liquid crystal cell, rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied.
The VA mode liquid crystal cell includes (1) a narrowly defined VA mode liquid crystal cell in which rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied, and substantially horizontally when a voltage is applied (Japanese Patent Laid-Open No. Hei 2-). 176625) (2) Liquid crystal cell (SID97, Digest of tech. Papers (Preliminary Proceed) 28 (1997) 845 in which the VA mode is made into a multi-domain (MVA mode) for widening the viewing angle ), (3) Liquid crystal cell in a mode (n-ASM mode) in which rod-like liquid crystalline molecules are substantially vertically aligned when no voltage is applied and twisted multi-domain alignment is applied when a voltage is applied (1998)), (4) SURVAVAL mode liquid crystal cell (announced at LCD International 98) and (5) CPA mode liquid crystal cell (announced at SID01) Is included.
[0085]
The OCB mode liquid crystal cell is a bend alignment mode liquid crystal cell in which rod-like liquid crystalline molecules are aligned in a substantially opposite direction (symmetrically) between the upper part and the lower part of the liquid crystal cell. Liquid crystal display devices using a bend alignment mode liquid crystal cell are disclosed in US Pat. Nos. 4,583,825 and 5,410,422. Since the rod-like liquid crystal molecules are symmetrically aligned at the upper and lower portions of the liquid crystal cell, the bend alignment mode liquid crystal cell has a self-optical compensation function. Therefore, this liquid crystal mode is also called an OCB (Optically Compensatory Bend) liquid crystal mode. The bend alignment mode liquid crystal display device has an advantage of high response speed.
The TN mode liquid crystal cell is most frequently used as a color TFT liquid crystal display device, and is described in many documents.
The ECB mode liquid crystal cell is one of the liquid crystal modes that has been studied since the oldest, and this is also described in many documents.
[0086]
【Example】
[Example 1]
(Preparation of cellulose acetate solution)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.
[0087]
────────────────────────────────────
Cellulose acetate solution composition
────────────────────────────────────
100 parts by mass of cellulose acetate having an acetylation degree of 60.9%
7.8 parts by mass of triphenyl phosphate (plasticizer)
Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by mass
300 parts by mass of methylene chloride (first solvent)
Methanol (second solvent) 54 parts by mass
1-butanol (third solvent) 11 parts by mass
────────────────────────────────────
[0088]
(Preparation of retardation increasing agent solution)
In another mixing tank, 16 parts by mass of the following retardation increasing agent, 80 parts by mass of methylene chloride and 20 parts by mass of methanol were added and stirred while heating to prepare a retardation increasing agent solution.
[0089]
[Chemical 9]

[0090]
(Preparation of transparent support)
A dope was prepared by mixing 475 parts by mass of the cellulose acetate solution with 25 parts by mass of the retardation increasing agent solution and stirring. The addition amount of the retardation increasing agent was 3.0 parts by mass with respect to 100 parts by mass of cellulose acetate.
The obtained dope was cast using a cooling drum casting machine to produce a cellulose acetate film used as a transparent support.
When the retardation value at a wavelength of 633 nm was measured for the produced cellulose acetate film using an ellipsometer (M-150, manufactured by JASCO Corporation), the Re retardation value was 10 nm and the Rth retardation value was 81 nm. It was.
[0091]
(Formation of undercoat layer)
On one surface of the transparent support, a coating solution having the following composition was 28 ml / m²This was coated and dried to form a gelatin subbing layer having a thickness of 0.1 μm.
[0092]
────────────────────────────────────
Undercoat layer coating solution composition
────────────────────────────────────
0.542 parts by weight of gelatin
0.135 parts by mass of formaldehyde
0.160 parts by mass of salicylic acid
39.1 parts by mass of acetone
15.8 parts by mass of methanol
40.6 parts by mass of methylene chloride
1.2 parts by weight of water
────────────────────────────────────
[0093]
(Formation of second undercoat layer)
On the undercoat layer, a coating solution having the following composition is 7 ml / m.²It was applied and dried to form a second undercoat layer.
[0094]
────────────────────────────────────
Second undercoat layer coating solution composition
────────────────────────────────────
0.079 parts by mass of the following anionic copolymer
Citric acid monoethyl ester 1.01 parts by mass
20 parts by mass of acetone
87.7 parts by mass of methanol
4.05 parts by mass of water
────────────────────────────────────
[0095]
[Chemical Formula 10]

[0096]
(Formation of back layer)
On the surface of the support opposite to the undercoat layer, a coating solution having the following composition was added at 25 ml / m.²It was applied and dried to form a back layer.
[0097]
────────────────────────────────────
Back layer coating composition
────────────────────────────────────
0.656 parts by mass of cellulose diacetate having an acetylation degree of 55%
0.065 parts by mass of silica-based matting agent having an average particle size of 1 μm
Acetone 67.9 parts by mass
10.4 parts by mass of methanol
────────────────────────────────────
[0098]
(Formation of alignment film)
On the second undercoat layer, a coating solution having the following composition was 28 ml / m with a # 16 wire bar coater.²Applied. Drying was performed with warm air of 60 ° C. for 60 seconds and further with warm air of 90 ° C. for 150 seconds.
Next, a rubbing treatment was performed on the formed film in the longitudinal direction of the cellulose acetate film (transparent support).
[0099]

[0100]
Embedded image

[0101]
(Formation of optically anisotropic layer)
On the alignment film, 41.01 g of the following discotic liquid crystalline molecules, 2.03 g of ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), dipentaerythritol hexaacrylate (KYARAD · DPHA, Nippon Kayaku Co., Ltd.) 2.03 g, cellulose acetate butyrate (CAB551-0.2, Eastman Chemical Co.) 0.90 g, cellulose acetate butyrate (CAB531-1, Eastman Chemical Co., Ltd.) A coating solution in which 0.23 g, a photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) 1.35 g, and a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.45 g were dissolved in 102 g of methyl ethyl ketone. And # 4 wire bar. This was attached to a metal frame and heated in a thermostatic chamber at 130 ° C. for 2 minutes to align the discotic liquid crystalline molecules. Next, in a state where the film surface temperature is about 100 ° C. in an atmosphere of 80 ° C., a 120 W / cm high-pressure mercury lamp is used to irradiate with ultraviolet rays for 0.4 seconds, so that a discotic liquid crystalline molecule, a polyfunctional monomer (dipenta Erythritol hexaacrylate) and alignment film polymer (modified polyvinyl alcohol) were copolymerized. Then, it stood to cool to room temperature. In this way, an optically anisotropic sheet was prepared by forming an optically anisotropic layer.
When the retardation value of the optically anisotropic layer was measured at a wavelength of 633 nm, the Re retardation value was 48 nm. The average angle (average inclination angle) between the disc surface of the discotic liquid crystalline molecules and the transparent support surface was 42 °.
[0102]
Embedded image

[0103]
(Preparation of polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film.
Next, the transparent support back layer side of the produced optical compensation sheet was attached to one side of the polarizing film using a polyvinyl alcohol-based adhesive. The slow axis of the transparent support and the transmission axis of the polarizing film were arranged in parallel.
Commercially available cellulose triacetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was saponified, using a polyvinyl alcohol adhesive as the transparent protective film, and the other side of the polarizing film (no optical compensation sheet attached) Pasted on the other side). The slow axis of the transparent protective film and the transmission axis of the polarizing film were arranged to be orthogonal.
In this way, a polarizing plate with an optical compensation sheet was produced.
[0104]
(Evaluation of reworkability)
The produced polarizing plate with an optical compensation sheet was attached to a glass plate through an adhesive. It arrange | positioned so that the optical compensation sheet side (optical anisotropic layer side) of a polarizing plate might turn into a glass surface side.
A polarizing plate with an optical compensation sheet attached to a glass plate was aged at 50 ° C. and 5 atm for 6 hours. Returning to the conditions of 25 ° C. and relative humidity 60 ° C., the polarizing plate with the optical compensation sheet was peeled from the glass plate.
When the above test operation was performed on 100 polarizing plates, all 100 polarizing plates were able to be peeled off from the glass plate without any problem (no peeling off).
[0105]
(Production of liquid crystal display device)
A pair of polarizing plates provided in a commercially available TN mode liquid crystal display device (6E-A3, manufactured by Sharp Corporation) is peeled off, and two optically produced polarizing plates are used instead of the optical compensation sheet on the liquid crystal cell side. As shown in FIG. In this way, a liquid crystal display device was produced. The transmission axis of the polarizing plate on the observer side and the transmission axis on the backlight side were arranged to be in the O mode.
About the produced liquid crystal display device, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using the measuring machine (EZ-Contrast160D, ELDIM company make). As a specific viewing angle, an angle with a contrast ratio of 10 or more and no black-side gradation inversion (inversion between L1 and L2) was obtained. As a result, a wide viewing angle of 70 ° on the upper side, 45 ° on the lower side, and 160 ° on the left and right was obtained.
[0106]
[Example 2]
(Preparation of cellulose acetate solution)
Two types of cellulose acetate solutions (inner layer dope and outer layer dope) comprising the following compositions were prepared. The inner layer dope was filtered through a filter paper (# 63, manufactured by Toyo Filter Paper Co., Ltd.) having an absolute filtration accuracy of 0.01 mm at 50 ° C. The outer layer dope was filtered at 50 ° C. with filter paper (FH025, manufactured by Pall) having an absolute filtration accuracy of 0.0025 mm.
[0107]
────────────────────────────────────
Cellulose acetate solution composition Inner layer dope Outer layer dope
────────────────────────────────────
Acetylation degree 60.5% Cellulose acetate 100 parts by weight 100 parts by weight
Triphenyl phosphate 7.8 parts by mass 7.8 parts by mass
Biphenyl diphenyl phosphate 3.9 parts by mass 3.9 parts by mass
Retardation increasing agent used in Example 1 3.0 parts by mass 3.0 parts by mass
Methylene chloride (first solvent) 450 parts by weight 481 parts by weight
Methanol (second solvent) 39 parts by mass 42 parts by mass
────────────────────────────────────
[0108]
(Preparation of transparent support)
Using a three-layer co-casting die, the inner layer dope was arranged on the inner side and the outer layer dope was on both outer sides thereof, and were simultaneously discharged onto the metal support to carry out multilayer casting. The casting amount was set so that the inner layer had a thickness of 45 μm and the outer layer had a thickness of 5 μm. The cast film was peeled from the support, uniaxially stretched 30% laterally with a tenter, and then dried to produce a cellulose acetate film. After drying at 70 ° C. for 3 minutes and at 120 ° C. for 5 minutes, the film was peeled off from the support and dried stepwise at 130 ° C. for 30 minutes to obtain a cellulose acetate film used as the support. The residual solvent amount was 0.5% by mass.
About the produced cellulose acetate film, when the retardation value in wavelength 633nm was measured using the ellipsometer (M-150, JASCO Corporation), Re retardation value was 38 nm and Rth retardation value was 230 nm. It was.
[0109]
(Saponification treatment of transparent support)
The transparent support was immersed in an aqueous 2.0N potassium hydroxide solution at 25 ° C. for 2 minutes, neutralized with sulfuric acid, washed with pure water, and dried. Then, when the surface energy of the transparent support was determined by the contact angle method, it was 63 mN / m.
[0110]
(Formation of alignment film)
On the saponified transparent support, an alignment film coating solution having the composition used in Example 1 was applied at 28 ml / m with a # 16 wire bar coater.²Applied. Drying was performed with warm air of 60 ° C. for 60 seconds and further with warm air of 90 ° C. for 150 seconds.
Next, the formed film was rubbed in a direction of 45 ° with respect to the longitudinal direction of the cellulose acetate film (transparent support).
[0111]
(Formation of optically anisotropic layer)
On the alignment film, 41.01 g of discotic liquid crystalline molecules used in Example 1, 1.22 g of ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), polyfunctional acrylate monomer (NK ester / A-TMMT, manufactured by Shin-Nakamura Chemical Co., Ltd.) 2.84 g, cellulose acetate butyrate (CAB551-0.2, manufactured by Eastman Chemical Co.) 0.90 g, cellulose acetate butyrate (CAB531-1) , Manufactured by Eastman Chemical Co., Ltd.) 0.23 g, photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy Co., Ltd.) 1.35 g, sensitizer (Kaya Cure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.45 g, 102 g A coating solution dissolved in methyl ethyl ketone was applied with a # 4 wire bar. This was attached to a metal frame and heated in a thermostatic chamber at 130 ° C. for 2 minutes to align the discotic liquid crystalline molecules. Next, in a state where the film surface temperature is about 100 ° C. in an atmosphere of 80 ° C., UV irradiation is performed for 0.4 seconds using a 120 W / cm high-pressure mercury lamp, and discotic liquid crystalline molecules, polyfunctional acrylate monomers and alignment are performed. A membrane polymer (modified polyvinyl alcohol) was copolymerized. Then, it stood to cool to room temperature. In this way, an optically anisotropic sheet was prepared by forming an optically anisotropic layer.
When the retardation value of the optically anisotropic layer was measured at a wavelength of 633 nm, the Re retardation value was 45 nm. Further, the average angle (average inclination angle) between the disc surface of the discotic liquid crystal molecules and the transparent support surface was 39 °.
[0112]
(Preparation of polarizing plate)
Using the produced optical compensation sheet, a polarizing plate was produced in the same manner as in Example 1 except that the slow axis of the transparent support and the transmission axis of the polarizing film were arranged at an angle of 45 °. .
[0113]
(Evaluation of reworkability)
The produced polarizing plate was affixed on the glass plate through the adhesive. The optical compensation sheet was placed on the glass surface side.
The polarizing plate attached to the glass plate was aged at 50 ° C. and 5 atm for 6 hours. It returned to the conditions of 25 degreeC and relative humidity 60 degreeC, and the polarizing plate was peeled from the glass plate.
When the above test operation was performed on 100 polarizing plates, all 100 polarizing plates were able to be peeled off from the glass plate without any problem (no peeling off).
[0114]
(Preparation of bend alignment liquid crystal cell)
A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and the alignment film was rubbed. The obtained two glass substrates were faced to each other so that the rubbing directions were parallel to each other, and the cell gap was set to 6 μm. A rod-like liquid crystal molecule (ZLI1132, manufactured by Merck & Co., Inc.) having a Δn of 0.1396 was injected into the cell gap to produce a bend alignment liquid crystal cell.
[0115]
(Production of liquid crystal display device)
Two produced polarizing plates were bonded so as to sandwich the produced bend alignment cell. The optically anisotropic layer of the polarizing plate faced the cell substrate, and the rubbing direction of the liquid crystal cell and the rubbing direction of the optically anisotropic layer facing it were antiparallel.
A rectangular wave voltage of 55 Hz was applied to the liquid crystal cell of the manufactured liquid crystal display device. A normally white mode of 2V white display and 5V black display was set. Using the measurement ratio (EZ-Contrast160D, manufactured by ELDIM) as a contrast ratio with the transmittance ratio (white display / black display), the viewing angle can be adjusted in eight stages from black display (L1) to white display (L8). It was measured. As a specific viewing angle, an angle with a contrast ratio of 10 or more and no black-side gradation inversion (inversion between L1 and L2) was obtained. As a result, a wide viewing angle of 80 ° on the upper side, 80 ° on the lower side, and 80 ° on the left and right sides was obtained.
[0116]
[Example 3]
(Preparation of cellulose acetate solution)
A cellulose acetate solution (dope) comprising the following composition was prepared.
[0117]
────────────────────────────────────
Cellulose acetate solution composition
────────────────────────────────────
100 parts by mass of cellulose acetate having an acetylation degree of 59.5%
7.8 parts by mass of triphenyl phosphate
3.9 parts by mass of biphenyl diphenyl phosphate
Retardation increasing agent used in Example 1 2.0 parts by mass
306 parts by mass of methyl acetate
122 parts by mass of cyclohexanone
30.5 parts by mass of methanol
30.5 parts by mass of ethanol
Silica fine particles having an average particle diameter of 20 nm 1.0 part by mass
────────────────────────────────────
[0118]
(Preparation of transparent support)
The prepared dope was cast on a metal support. After drying at 70 ° C. for 3 minutes and at 120 ° C. for 5 minutes, the film was peeled off from the support and dried at 130 ° C. for 50 minutes to obtain a cellulose acetate film used as the support. The residual solvent amount was 0.8% by mass.
About the produced cellulose acetate film, when the retardation value in wavelength 633nm was measured using the ellipsometer (M-150, JASCO Corporation make), Re retardation value was 10 nm and Rth retardation value was 50 nm. It was.
[0119]
(Saponification treatment of transparent support)
A 2.0N potassium hydroxide aqueous solution was applied to the transparent support at 70 ° C., washed with pure water after 30 seconds, and dried. Then, when the surface energy of the transparent support was determined by a contact angle method, it was 65 mN / m.
[0120]
(Formation of alignment film and optically anisotropic layer)
An alignment film and an optically anisotropic layer were formed on the saponified surface of the cellulose acetate film in the same manner as in Example 1 (without providing an undercoat layer).
In this way, an optical compensation sheet was produced.
[0121]
[Example 4]
(Saponification treatment of transparent support)
A 1.5 N potassium hydroxide solution (solvent: water / isopropyl alcohol / polyethylene glycol = 14/86/15 vol%) was added to the transparent support prepared in Example 1 at 5 ml / m.²It was applied and held at 60 ° C. for about 10 seconds. The potassium hydroxide remaining on the film surface was washed with water and dried. The surface energy of the transparent support was determined by a contact angle method and found to be 63 mN / m.
[0122]
(Formation of alignment film and optically anisotropic layer)
An alignment film and an optically anisotropic layer were formed on the saponified surface of the cellulose acetate film in the same manner as in Example 1 (without providing an undercoat layer).
In this way, an optical compensation sheet was produced.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a basic configuration of a transmissive liquid crystal display device.
FIG. 2 is a schematic diagram showing another basic configuration of a transmissive liquid crystal display device.
FIG. 3 is a schematic diagram showing still another basic configuration of a transmissive liquid crystal display device.
FIG. 4 is a schematic diagram showing a basic configuration of a reflective liquid crystal display device.
[Explanation of symbols]
BL backlight
RP reflector
1, 1a, 1b, 3, 3a, 3b Transparent protective film
2, 2a, 2b Polarizing film
4, 4a, 4b Transparent support
5, 5a, 5b Optically anisotropic layer
6a, 6b Liquid crystal cell substrate
7 Rod-like liquid crystalline molecules

Claims (12)

An optical compensation sheet comprising an optically anisotropic layer formed from liquid crystalline molecules and a transparent support, wherein the optically anisotropic layer is a polymer of a polyfunctional monomer having four or more double bonds in the molecule An optical compensation sheet comprising: The optical compensation sheet according to claim 1, wherein the polyfunctional monomer is an ester of a polyol having 4 or more hydroxyl groups in the molecule and acrylic acid or methacrylic acid. The optical compensation sheet according to claim 1, wherein the liquid crystal molecules are discotic liquid crystal molecules. The optical compensation sheet according to claim 3, wherein the discotic liquid crystalline molecule has a double bond, and the discotic liquid crystalline molecule and the polyfunctional monomer are copolymerized. The optical compensation sheet according to claim 1, wherein an alignment film is provided between the optically anisotropic layer and the transparent support. 6. The optical compensation sheet according to claim 5, wherein the alignment film is made of a polymer having a double bond in the side chain, and the alignment film polymer and the polyfunctional monomer are copolymerized. The optical compensation sheet according to claim 1, wherein the transparent support has a Re retardation value of 0 to 50 nm and an Rth retardation value of 70 to 400 nm. The optical compensation sheet according to claim 1, wherein the transparent support comprises a cellulose acetate film having an acetylation degree of 59.0 to 61.5%. The optical compensation sheet according to claim 8, wherein the cellulose acetate film contains 0.01 to 20 parts by mass of an aromatic compound having at least two aromatic rings with respect to 100 parts by mass of the cellulose acetate. The optical compensation sheet according to claim 8, wherein the cellulose acetate film is formed by a co-casting method. The cellulose acetate film is formed into a film from a cellulose acetate solution using an ether having 2 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, or an ester having 2 to 12 carbon atoms as a solvent. The optical compensation sheet as described. A liquid crystal display device comprising a liquid crystal cell and two polarizing plates disposed on both sides thereof, wherein at least one optical compensation sheet is disposed between the liquid crystal cell and at least one polarizing plate, and the optical compensation The sheet has an optically anisotropic layer formed from liquid crystalline molecules and a transparent support, and the transparent support may function as a transparent protective film for the polarizing plate, and the optically anisotropic layer is further contained in the molecule. A liquid crystal display device comprising a polymer of a polyfunctional monomer having four or more double bonds.

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