JP3896403B2 - Optical compensation sheet, STN type liquid crystal display device, and method for aligning discotic liquid crystal molecules - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid coloring of a display image and to obtain a sharp image with high contrast by incorporating a specified polymer into the side chains of an alignment layer and aligning discotic liquid crystal molecules at a specified average tilt angle. SOLUTION: As for a liquid crystal cell, a liquid crystal layer is formed by sealing rodlike liquid crystal molecules 13a to 13e between an alignment layer 12 on the lower side of an upper substrate 11 and an alignment layer 14 on the upper side of a lower substrate 15. An optical compensation sheet is disposed under the liquid crystal cell. The optical compensation sheet has an alignment layer 22 and optical anisotropic layer formed in this order on a transparent supporting body 23. The optical anisotropic layer is produced by aligning discotic liquid crystal molecules 21a to 21e and fixing the molecules in the aligned state. A polymer having 2 to 4 aromatic groups or aromatic heterorings is incorporated into the side chains of the alignment layer so as to align the discotic liquid crystal molecules at 50 deg. to 90 deg. average tilt angle. Thereby, the discotic liquid crystal molecules can be stably aligned.

Description

【００３０】
【化２】

【００３１】
【化３】

【００３２】
【化４】

【００３３】
ジアミン起源の繰り返し単位の例を以下に示す。
【００３４】
【化５】

【００３５】
【化６】

【００３６】
【化７】

【００３７】
【化８】

【００３８】
【化９】

【００３９】
【化１０】

【００４０】
【化１１】

【００４１】
【化１２】

【００４２】
ポリイミドの末端に、繰り返し単位とは異なる基が結合していてもよい。末端基（Ｅ）の例を以下に示す。
【００４３】
【化１３】

【００４４】
配向膜に好ましく用いることができる側鎖に炭化水素基を有するポリイミド、および主鎖と側鎖とに炭化水素基を有するポリイミドの例を、テトラカルボン酸起源の繰り返し単位（Ａ）、ジアミン起源の繰り返し単位（Ｂ）および末端基（Ｅ）の番号を引用しながら示す。コポリマー中の繰り返し単位の割合は、モル％である。
【００４５】
ＰＩ１：−Ａ１−Ｂ１−
ＰＩ２：−（Ａ１−Ｂ１）₈₀−（Ａ１−Ｂ２）₂₀−
ＰＩ３：−Ａ２−Ｂ４−
ＰＩ４：−Ａ３−Ｂ４−
ＰＩ５：−（Ａ４−Ｂ１１）₉₀−（Ａ４−Ｂ２１）₁₀−
ＰＩ６：−（Ａ４−Ｂ１１）₈₀−（Ａ４−Ｂ２１）₂₀−
ＰＩ７：−（Ａ４−Ｂ１１）₇₀−（Ａ４−Ｂ２１）₃₀−
ＰＩ８：−Ａ４−Ｂ１１−
ＰＩ９：−Ａ５−Ｂ３２−
ＰＩ10：−Ａ７−Ｂ２３−
ＰＩ11：−Ａ８−Ｂ１−
ＰＩ12：−Ａ８−Ｂ６−
ＰＩ13：−Ａ９−Ｂ１２−
ＰＩ14：−Ａ１０−Ｂ１８−
ＰＩ15：−Ａ１１−Ｂ２２−
ＰＩ16：−Ａ１２−Ｂ２７−
【００４６】
ＰＩ17：Ｅ２−（Ａ１−Ｂ１）−Ｅ５
ＰＩ18：Ｅ４−（Ａ７−Ｂ２１）−Ｅ８
【００４７】
ＰＩ19：−（Ａ８−Ｂ２１）₈₀−（Ａ１４−Ｂ２１）₂₀−
ＰＩ20：−（Ａ８−Ｂ２１）₉₀−（Ａ１５−Ｂ２１）₁₀−
ＰＩ21：−（Ａ８−Ｂ２１）₉₀−（Ａ８−Ｂ５９）₁₀−
【００４８】
炭素原子数が１２以上の炭化水素基を含むポリアミック酸も配向膜に用いることができる。ポリアミック酸は、テトラカルボン酸とジアミンとの部分縮合反応により合成する。すなわち、テトラカルボン酸の四個のカルボキシルのうち二つとジアミンとを反応させてアミド結合を形成する。テトラカルボン酸の残り二個のカルボキシルは、ポリアミック酸中に残存する。
ポリアミック酸のままでも、配向膜として機能できる。また、ポリアミック酸を加熱して、脱水閉環させポリイミドにしてから、配向膜として利用することもできる。ポリアミック酸を短時間または低温で加熱することにより、部分的に脱水閉環させ、得られるポリアミック酸とポリイミドとのコポリマーを配向膜として用いてもよい。
【００４９】
配向膜に用いるポリマーの重合度は、２００乃至５０００であることが好ましく、３００乃至３０００であることが好ましい。ポリマーの分子量は、９０００乃至２０００００であることが好ましく、１３０００乃至１３００００であることがさらに好ましい。
二種類以上のポリマーを併用してもよい。
【００５０】
配向膜に用いるポリマーを架橋させてもよい。架橋反応は、配向膜の塗布液の塗布と同時または塗布後に実施することが好ましい。
ポリマーの架橋は、架橋剤を用いて形成できる。架橋剤の例には、エポキシ化合物（例、グリセロールポリグリシジルエーテル、ポリグリセロールポリグリシジルエーテル、ポリエチレングリコールジグリシジルエーテル）、アルデヒド（例、ホルムアルデヒド、グリオキサール、グルタルアルデヒド、マロンアルデヒド、フタルアルデヒド、テレフタルアルデヒド、スクシンアルデヒド、イソフタルアルデヒド、ジアルデヒド澱粉）、Ｎ−メチロール化合物（例、ジメチロール尿素、メチロールジメチルヒダントイン）、ジオキサン（例、２，３−ジヒドロキシジオキサン）、カルベニウム、２−ナフタレートスルホナート、１，１−ビスピロリジノ−１−クロロピリジニウム、１−モルホリノカルボニル−３−（スルホナトアミノメチル）、活性ビニル化合物（例、１，３，５−トリアクリロイル−ヘキサヒドロ−ｓ−トリアジン、ビス（ビニルスルホン）メタン、Ｎ，Ｎ’−メチレンビス−［β−（ビニスルホニル）プロピオンアミド）、活性ハロゲン化合物（例、２，４−ジクロロ−６−ヒドロキシ−ｓ−トリアジン）およびイソオキサゾール類が含まれる。ポリマーがポリイミドまたはポリアミック酸である場合は、架橋剤としてエポキシ化合物を用いることが好ましい。
【００５１】
配向膜の厚さは、０．１乃至１０μｍであることが好ましい。
配向膜の形成において、ラビング処理を実施することが好ましい。ラビング処理は、上記のポリマーを含む膜の表面を、紙や布で一定方向に、数回こすることにより実施する。
なお、配向膜を用いてディスコティック液晶性分子を実質的に垂直に配向させてから、その配向状態のままディスコティック液晶性分子を固定して光学的異方性層を形成し、光学的異方性層のみを透明支持体上に転写してもよい。配向状態が固定されたディスコティック液晶性分子は、配向膜がなくても配向状態を維持することができる。
【００５２】
［光学的異方性層］
光学的異方性層はディスコティック液晶性分子を含む。
光学的異方性層では、上記の配向膜を用いて、ディスコティック液晶性分子の円盤面を、配向膜に対して、実質的に垂直（５０乃至９０度の範囲の平均傾斜角）に配向させる。ディスコティック液晶性分子は、垂直（ホモジニアス）配向状態のまま光学的異方性層内で固定することが好ましい。ディスコティック液晶性分子は、重合反応により固定することがさらに好ましい。
ディスコティック液晶性分子は、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。ディスコティック液晶性分子の重合については、特開平８−２７２８４公報に記載がある。
ディスコティック液晶性分子を重合により固定するためには、ディスコティック液晶性分子の円盤状コアに、置換基として重合性基を結合させる必要がある。ただし、円盤状コアに重合性基を直結させると、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基との間に、連結基を導入する。従って、重合性基を有するディスコティック液晶性分子は、下記式で表わされる化合物であることが好ましい。
【００５３】
Ｄ（−Ｌ−Ｑ）_n
式中、Ｄは円盤状コアであり；Ｌは二価の連結基であり；Ｑは重合性基であり；そして、ｎは４乃至１２の整数である。
上記式の円盤状コア（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。
【００５４】
【化１４】

【００５５】
【化１５】

【００５６】
【化１６】

【００５７】
【化１７】

【００５８】
【化１８】

【００５９】
【化１９】

【００６０】
【化２０】

【００６１】
上記式において、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、アルケニレン基、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、アルケニレン基、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い。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。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、ハロゲン原子、シアノ、アルコキシ基、アシルオキシ基）を有していてもよい。
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を意味し、ＡＲはアリーレン基を意味する。
【００６２】
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−
Ｌ11：−Ｏ−ＡＬ−
Ｌ12：−Ｏ−ＡＬ−Ｏ−
Ｌ13：−Ｏ−ＡＬ−Ｏ−ＣＯ−
【００６３】
Ｌ14：−Ｏ−ＡＬ−Ｏ−ＣＯ−ＮＨ−ＡＬ−
Ｌ15：−Ｏ−ＡＬ−Ｓ−ＡＬ−
Ｌ16：−Ｏ−ＣＯ−ＡＬ−ＡＲ−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ17：−Ｏ−ＣＯ−ＡＲ−Ｏ−ＡＬ−ＣＯ−
Ｌ18：−Ｏ−ＣＯ−ＡＲ−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ19：−Ｏ−ＣＯ−ＡＲ−Ｏ−ＡＬ−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ20：−Ｏ−ＣＯ−ＡＲ−Ｏ−ＡＬ−Ｏ−ＡＬ−Ｏ−ＡＬ−Ｏ−ＣＯ−
Ｌ21：−Ｓ−ＡＬ−
Ｌ22：−Ｓ−ＡＬ−Ｏ−
Ｌ23：−Ｓ−ＡＬ−Ｏ−ＣＯ−
Ｌ24：−Ｓ−ＡＬ−Ｓ−ＡＬ−
Ｌ25：−Ｓ−ＡＲ−ＡＬ−
【００６４】
ＡＬ（アルキレン基またはアルケニレン基）に、不斉炭素原子を導入すると、ディスコティック液晶性分子を螺旋状にねじれ配向させることができる。不斉炭素原子を含むＡＬ＊の例を以下に挙げる。左側が円盤状コア（Ｄ）側であり、右側が重合性基（Ｑ）側である。＊印を付けた炭素原子（Ｃ）が不斉炭素原子である。光学活性は、ＳとＲのいずれでもよい。
【００６５】
ＡＬ＊１：−ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊２：−ＣＨ₂ ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ −
ＡＬ＊３：−ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊４：−Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊５：−ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ −
ＡＬ＊６：−ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −
ＡＬ＊７：−Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊８：−ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊９：−ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ −
ＡＬ＊10：−ＣＨ₂ ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ −
ＡＬ＊11：−ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −
ＡＬ＊12：−Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊13：−ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ −
ＡＬ＊14：−ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ −
ＡＬ＊15：−ＣＨ₂ ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −
【００６６】
ＡＬ＊16：−ＣＨ₂ −Ｃ＊ＨＣＨ₃ −
ＡＬ＊17：−Ｃ＊ＨＣＨ₃ −ＣＨ₂ −
ＡＬ＊18：−Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊19：−ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊20：−ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊21：−ＣＨ₂ ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊22：−Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊23：−ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊24：−ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊25：−ＣＨ₂ ＣＨ₂ ＣＨ₂ −Ｃ＊ＨＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊26：−Ｃ＊ＨＣＨ₃ −（ＣＨ₂ ）₈ −
ＡＬ＊27：−ＣＨ₂ −Ｃ＊ＨＣＨ₃ −（ＣＨ₂ ）₈ −
ＡＬ＊28：−ＣＨ₂ −Ｃ＊ＨＣＨ₂ＣＨ₃ −
ＡＬ＊29：−ＣＨ₂ −Ｃ＊ＨＣＨ₂ＣＨ₃ −ＣＨ₂ −
ＡＬ＊30：−ＣＨ₂ −Ｃ＊ＨＣＨ₂ＣＨ₃ −ＣＨ₂ ＣＨ₂ −
【００６７】
ＡＬ＊31：−ＣＨ₂ −Ｃ＊ＨＣＨ₂ＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊32：−ＣＨ₂ −Ｃ＊Ｈ（ｎ−Ｃ₃ Ｈ₇ ）−ＣＨ₂ ＣＨ₂ −
ＡＬ＊33：−ＣＨ₂ −Ｃ＊Ｈ（ｎ−Ｃ₃ Ｈ₇ ）−ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊34：−ＣＨ₂ −Ｃ＊Ｈ（ＯＣＯＣＨ₃ ）−ＣＨ₂ ＣＨ₂ −
ＡＬ＊35：−ＣＨ₂ −Ｃ＊Ｈ（ＯＣＯＣＨ₃ ）−ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊36：−ＣＨ₂ −Ｃ＊ＨＦ−ＣＨ₂ ＣＨ₂ −
ＡＬ＊37：−ＣＨ₂ −Ｃ＊ＨＦ−ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊38：−ＣＨ₂ −Ｃ＊ＨＣｌ−ＣＨ₂ ＣＨ₂ −
ＡＬ＊39：−ＣＨ₂ −Ｃ＊ＨＣｌ−ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊40：−ＣＨ₂ −Ｃ＊ＨＯＣＨ₃ −ＣＨ₂ ＣＨ₂ −
ＡＬ＊41：−ＣＨ₂ −Ｃ＊ＨＯＣＨ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊42：−ＣＨ₂ −Ｃ＊ＨＣＮ−ＣＨ₂ ＣＨ₂ −
ＡＬ＊43：−ＣＨ₂ −Ｃ＊ＨＣＮ−ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
ＡＬ＊44：−ＣＨ₂ −Ｃ＊ＨＣＦ₃ −ＣＨ₂ ＣＨ₂ −
ＡＬ＊45：−ＣＨ₂ −Ｃ＊ＨＣＦ₃ −ＣＨ₂ ＣＨ₂ ＣＨ₂ ＣＨ₂ −
【００６８】
前記式の重合性基（Ｑ）は、重合反応の種類に応じて決定する。重合性基（Ｑ）の例を以下に示す。
【００６９】
【化２１】

【００７０】
重合性基（Ｑ）は、不飽和重合性基（Ｑ１〜Ｑ７）、エポキシ基（Ｑ８）またはアジリジニル基（Ｑ９）であることが好ましく、不飽和重合性基であることがさらに好ましく、エチレン性不飽和重合性基（Ｑ１〜Ｑ６）であることが最も好ましい。
前記式において、ｎは４乃至１２の整数である。具体的な数字は、ディスコティックコア（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。
二種類以上のディスコティック液晶性分子を併用してもよい。例えば、二価の連結基に不斉炭素原子を有する分子と有していない分子を併用することができる。また、重合性基（Ｑ）を有する分子と有していない分子を併用してもよい。不斉炭素原子を有し重合性基を有していない分子と、重合性基を有し不斉炭素原子を有していない分子を併用することが特に好ましい。この場合は、重合性基を有し不斉炭素原子を有していない分子のみがディスコティック液晶性分子として機能し、不斉炭素原子を有し重合性基を有していない分子はカイラル剤（後述）として機能していると考えることもできる。
【００７１】
非重合性ディスコティック液晶性分子は、前述した重合性ディスコティック液晶性分子の重合性基（Ｑ）を、水素原子またはアルキル基に変更した化合物であることが好ましい。すなわち、非重合性ディスコティック液晶性分子は、下記式で表わされる化合物であることが好ましい。
Ｄ（−Ｌ−Ｒ）_n
式中、Ｄは円盤状コアであり；Ｌは二価の連結基であり；Ｒは水素原子またはアルキル基であり；そして、ｎは４乃至１２の整数である。
上記式の円盤状コア（Ｄ）の例は、ＬＱ（またはＱＬ）をＬＲ（またはＲＬ）に変更する以外は、前記の重合性ディスコティック液晶分子の例と同様である。また、二価の連結基（Ｌ）の例も、前記の重合性ディスコティック液晶分子の例と同様である。
Ｒのアルキル基は、炭素原子数が１乃至４０であることが好ましく、１乃至３０であることがさらに好ましい。環状アルキル基よりも鎖状アルキル基の方が好ましく、分岐を有する鎖状アルキル基よりも直鎖状アルキル基の方が好ましい。Ｒは、水素原子または炭素原子数が１乃至３０の直鎖状アルキル基であることが特に好ましい。
【００７２】
ディスコティック液晶性分子の二価の連結基（Ｌ）に不斉炭素原子を導入する代わりに、不斉炭素原子を含む光学活性を示す化合物（カイラル剤）を光学的異方性層に添加しても、ディスコティック液晶性分子を螺旋状にねじれ配向させることができる。不斉炭素原子を含む化合物としては、様々な天然または合成化合物が使用できる。不斉炭素原子を含む化合物中には、ディスコティック液晶性分子と同じまたは類似の重合性基を導入してもよい。重合性基を導入すると、ディスコティック液晶性分子を実質的に垂直（ホモジニアス）配向させた後に、固定するのと同時に、同じまたは類似の重合反応により不斉炭素原子を含む化合物も光学的異方性層内で固定することができる。
【００７３】
ディスコティック液晶性分子を空気界面側においても、実質的に垂直（ホモジニアス）かつ均一に配向させるため、含フッ素界面活性剤またはセルロースエステルを光学的異方性層に添加することができる。
含フッ素界面活性剤は、フッ素原子を含む疎水性基、ノニオン性、アニオン性、カチオン性あるいは両性の親水性基および任意に設けられる連結基からなる。一つの疎水性基と一つの親水性基からなる含フッ素界面活性剤は、下記式で表わされる。
Ｒｆ−Ｌ⁵ −Ｈｙ
式中、Ｒｆは、フッ素原子で置換された一価の炭化水素基であり、Ｌ⁵ は、単結合または二価の連結基であり、そして、Ｈｙは親水性基である。
上記のＲｆは、疎水性基として機能する。炭化水素基は、アルキル基またはアリール基であることが好ましい。アルキル基の炭素原子数は３乃至３０であることが好ましく、アリール基の炭素原子数は６乃至３０であることが好ましい。
炭化水素基に含まれる水素原子の一部または全部は、フッ素原子で置換されている。フッ素原子で、炭化水素基に含まれる水素原子の５０％以上を置換することが好ましく、６０％以上を置換することがより好ましく、７０％以上を置換することがさらに好ましく、８０％以上を置換することが最も好ましい。
残りの水素原子は、さらに他のハロゲン原子（例、塩素原子、臭素原子）で置換されていてもよい。
Ｒｆの例を以下に示す。
【００７４】
Ｒｆ１：ｎ−Ｃ₈ Ｆ₁₇−
Ｒｆ２：ｎ−Ｃ₆ Ｆ₁₃−
Ｒｆ３：Ｃｌ−（ＣＦ₂ −ＣＦＣｌ）₃ −ＣＦ₂ −
Ｒｆ４：Ｈ−（ＣＦ₂ ）₈ −
Ｒｆ５：Ｈ−（ＣＦ₂ ）₁₀−
Ｒｆ６：ｎ−Ｃ₉ Ｆ₁₉−
Ｒｆ７：ペンタフルオロフェニル
Ｒｆ８：ｎ−Ｃ₇ Ｆ₁₅−
Ｒｆ９：Ｃｌ−（ＣＦ₂ −ＣＦＣｌ）₂ −ＣＦ₂ −
Ｒｆ10：Ｈ−（ＣＦ₂ ）₄ −
Ｒｆ11：Ｈ−（ＣＦ₂ ）₆ −
Ｒｆ12：Ｃｌ−（ＣＦ₂ ）₆ −
Ｒｆ13：Ｃ₃ Ｆ₇ −
【００７５】
前記式において、二価の連結基は、アルキレン基、アリーレン基、二価のヘテロ環残基、−ＣＯ−、−ＮＲ−（Ｒは炭素原子数が１乃至５のアルキル基または水素原子）、−Ｏ−、−ＳＯ₂ −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。
前記式のＬ⁵ の例を以下に示す。左側が疎水性基（Ｒｆ）に結合し、右側が親水性基（Ｈｙ）に結合する。ＡＬはアルキレン基、ＡＲはアリーレン基、Ｈｃは二価のヘテロ環残基を意味する。なお、アルキレン基、アリーレン基および二価のヘテロ環残基は、置換基（例、アルキル基）を有していてもよい。
【００７６】
Ｌ０：単結合
Ｌ51：−ＳＯ₂ −ＮＲ−
Ｌ52：−ＡＬ−Ｏ−
Ｌ53：−ＣＯ−ＮＲ−
Ｌ54：−ＡＲ−Ｏ−
Ｌ55：−ＳＯ₂ −ＮＲ−ＡＬ−ＣＯ−Ｏ−
Ｌ56：−ＣＯ−Ｏ−
Ｌ57：−ＳＯ₂ −ＮＲ−ＡＬ−Ｏ−
Ｌ58：−ＳＯ₂ −ＮＲ−ＡＬ−
Ｌ59：−ＣＯ−ＮＲ−ＡＬ−
Ｌ60：−ＡＬ−Ｏ−ＡＬ−
Ｌ61：−Ｈｃ−ＡＬ−
Ｌ62：−ＳＯ₂ −ＮＲ−ＡＬ−Ｏ−ＡＬ−
Ｌ63：−ＡＲ−
Ｌ64：−Ｏ−ＡＲ−ＳＯ₂ −ＮＲ−ＡＬ−
Ｌ65：−Ｏ−ＡＲ−ＳＯ₂ −ＮＲ−
Ｌ66：−Ｏ−ＡＲ−Ｏ−
【００７７】
前記式のＨｙは、ノニオン性親水性基、アニオン性親水性基、カチオン性親水性基あるいは両性親水性基のいずれかである。ノニオン性親水性基が特に好ましい。
前記式のＨｙの例を以下に示す。
【００７８】
Ｈｙ１：−（ＣＨ₂ ＣＨ₂ Ｏ）_n −Ｈ（ｎは５乃至３０の整数）
Ｈｙ２：−（ＣＨ₂ ＣＨ₂ Ｏ）_n −Ｒ¹
（ｎは５乃至３０の整数、Ｒ¹ は炭素原子数が１乃至６のアルキル基）
Ｈｙ３：−（ＣＨ₂ ＣＨＯＨＣＨ₂ ）_n −Ｈ（ｎは５乃至３０の整数）
Ｈｙ４：−ＣＯＯＭ（Ｍは水素原子、アルカリ金属原子または解離状態）
Ｈｙ５：−ＳＯ₃ Ｍ（Ｍは水素原子、アルカリ金属原子または解離状態）
Ｈｙ６：−（ＣＨ₂ ＣＨ₂ Ｏ）_n −ＣＨ₂ ＣＨ₂ ＣＨ₂ −ＳＯ₃ Ｍ
（ｎは５乃至３０の整数、Ｍは水素原子またはアルカリ金属原子）
Ｈｙ７：−ＯＰＯ（ＯＨ）₂
Ｈｙ８：−Ｎ⁺ （ＣＨ₃ ）₃ ・Ｘ^- （Ｘはハロゲン原子）
Ｈｙ９：−ＣＯＯＮＨ₄
【００７９】
ノニオン性親水性基（Ｈｙ１、Ｈｙ２、Ｈｙ３）が好ましく、ポリエチレンオキサイドからなる親水性基（Ｈｙ１）が最も好ましい。
フッ素原子を含む疎水性基または親水性基を二以上有する含フッ素界面活性剤を用いてもよい。二種類以上の含フッ素界面活性剤を併用してもよい。
含フッ素界面活性剤については、様々な文献（例、堀口弘著「新界面活性剤」三共出版(1975)、M.J. Schick, Nonionic Surfactants, Marcell Dekker Inc., New York, (1967)、特開平７−１３２９３号公報）に記載がある。
含フッ素界面活性剤は、ディスコティック液晶性分子の量の０．０１乃至３０重量％の範囲であることが好ましく、０．０５乃至１０重量％であることがさらに好ましく、０．１乃至５重量％であることがさらに好ましい。
【００８０】
セルロースエステルとしては、セルロースの低級脂肪酸エステルを用いることが好ましい。
セルロースの低級脂肪酸エステルにおける「低級脂肪酸」とは、炭素原子数が６以下の脂肪酸を意味する。炭素原子数は、２乃至５であることが好ましく、２乃至４であることがさらに好ましい。脂肪酸には置換基（例、ヒドロキシ）が結合していてもよい。二種類以上の脂肪酸がセルロースとエステルを形成していてもよい。セルロースの低級脂肪酸エステルの例には、セルロースアセテート、セルロースプロピオネート、セルロースブチレート、セルロースヒドロキシプロピオネート、セルロースアセテートプロピオネートおよびセルロースアセテートブチレートが含まれる。セルロースアセテートブチレートが特に好ましい。セルロースアセテートブチレートのブチリル化度は、３０％以上であることが好ましく、３０乃至８０％であることがさらに好ましい。セルロースアセテートブチレートのアセチル化度は、３０％以下であることが好ましく、１乃至３０％であることがさらに好ましい。
セルロースエステルは、０．００５乃至０．５ｇ／ｍ² の範囲の量で使用することが好ましく、０．０１乃至０．４５ｇ／ｍ² の範囲であることがより好ましく、０．０２乃至０．４／ｍ² の範囲であることがさらに好ましく、０．０３乃至０．３５／ｍ² の範囲であることが最も好ましい。また、ディスコティック液晶性分子の量の０．１乃至５重量％の量で使用することも好ましい。
【００８１】
光学的異方性層は、ディスコティック液晶性分子、さらに必要に応じて不斉炭素原子を含む化合物、含フッ素界面活性剤、セルロースエステル、あるいは下記の重合開始剤や他の添加剤を含む塗布液を、配向膜の上に塗布することで形成する。
塗布液の調製に使用する溶媒としては、有機溶媒が好ましく用いられる。有機溶媒の例には、アミド（例、Ｎ，Ｎ−ジメチルホルムアミド）、スルホキシド（例、ジメチルスルホキシド）、ヘテロ環化合物（例、ピリジン）、炭化水素（例、ベンゼン、ヘキサン）、アルキルハライド（例、クロロホルム、ジクロロメタン）、エステル（例、酢酸メチル、酢酸ブチル）、ケトン（例、アセトン、メチルエチルケトン）、エーテル（例、テトラヒドロフラン、１，２−ジメトキシエタン）が含まれる。アルキルハライドおよびケトンが好ましい。二種類以上の有機溶媒を併用してもよい。
【００８２】
塗布液の塗布は、公知の方法（例、押し出しコーティング法、ダイレクトグラビアコーティング法、リバースグラビアコーティング法、ダイコーティング法、バーコーティング法）により実施できる。
実質的に垂直（ホモジニアス）配向させたディスコティック液晶性分子は、配向状態を維持して固定する。固定化は、ディスコティック液晶性分子に導入した重合性基（Ｑ）の重合反応により実施することが好ましい。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。
【００８３】
光重合開始剤の使用量は、塗布液の固形分の０．０１乃至２０重量％であることが好ましく、０．５乃至５重量％であることがさらに好ましい。
ディスコティック液晶性分子の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、２０ｍＪ／ｃｍ² 乃至５０Ｊ／ｃｍ² であることが好ましく、１００乃至２０００ｍＪ／ｃｍ² であることがさらに好ましい。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。
光学的異方性層の厚さは、０．１乃至５０μｍであることが好ましく、１乃至３０μｍであることがさらに好ましく、５乃至２０μｍであることが最も好ましい。なお、液晶表示装置に光学補償シートを二枚用いる場合は、一枚使用する場合に必要とされる光学的異方性層の厚さ（上記の好ましい範囲）の半分の厚さでよい。
光学的異方性層内のディスコティック液晶性分子の平均傾斜角度は、５０乃至９０度である。傾斜角度は、なるべく均一であることが好ましい。ただし、傾斜角度が光学的異方性層の厚み方向に沿って連続して変化しているならば、若干の変動があっても問題ない。
【００８４】
ディスコティック液晶性分子のねじれの角度（ツイスト角）は、ＳＴＮ型液晶セルのツイスト角（一般に１８０乃至３６０度、好ましくは１８０度を越えて２７０度まで）に応じて、類似（なるべく±１０度以内）の角度となるように調整することが好ましい。液晶表示装置に光学補償シートを一枚用いる場合は、ディスコティック液晶性分子のねじれ角は、１８０乃至３６０度の範囲であることが好ましい。液晶表示装置に光学補償シートを二枚用いる場合は、ディスコティック液晶性分子のねじれ角は、９０乃至１８０度の範囲であることが好ましい。
光学補償シートをＳＴＮ型液晶表示装置に用いる場合、光学的異方性層の複屈折率の波長依存性（Δｎ（λ））は、ＳＴＮ型液晶セルの液晶の複屈折率の波長依存性に近い値であることが好ましい。
【００８５】
［液晶表示装置］
前述したように、本発明は、ＳＴＮ型液晶セルを用いる液晶表示装置において特に有効である。
ＳＴＮ型液晶表示装置は、ＳＴＮ型液晶セル、液晶セルの片側または両側に配置された一枚または二枚の光学補償シートおよびそれらの両側に配置された一対の偏光板からなる。
液晶セルの棒状液晶性分子の配向方向とディスコティック液晶性分子の配向方向との関係は、光学補償シートに最も近い液晶セルの棒状液晶性分子のディレクタ（棒状分子の長軸方向）と、液晶セルに最も近い光学補償シートのディスコティック液晶性分子のディレクタ（円盤状コア平面の法線方向）とが、液晶セルの法線方向から見て、実質的に同じ向き（±１０゜未満）になるように配置することが好ましい。
光学補償シートの透明支持体を、偏光膜の液晶セル側の保護膜としても機能させることができる。その場合は、透明支持体の遅相軸（屈折率が最大となる方向）と偏光膜の透過軸とが実質的に垂直または実質的に平行（±１０゜未満）になるように配置することが好ましい。
【００８６】
【実施例】
［実施例１］
厚さ１００μｍ、サイズ２７０ｍｍ×１００ｍｍのトリアセチルセルロースフイルム（フジタック、富士写真フイルム（株）製）を透明支持体として用いた。側鎖に芳香族環または芳香族性複素環を有するポリイミド（ＰＩ１）をメタノールとアセトンとの混合溶媒（容量比＝５０／５０）に溶解して、５重量％溶液を調製した。この溶液をバーコーターを用いて透明支持体の上に１μｍの厚さに塗布した。塗布層を、１３０℃の温風で２分間乾燥し、その表面をラビング処理して、配向膜を形成した。
配向膜の上に、以下の組成の塗布液をエクストルージョン法により塗布した。
【００８７】

【００８８】
【化２２】

【００８９】
【化２３】

【００９０】
【化２４】

【００９１】
塗布層を１３０℃で２分間加熱して、ディスコティック液晶性化合物を実質的に垂直に配向させた。その温度で、４秒間紫外線を照射し、ディスコティック液晶性化合物を重合させ、配向状態を固定した。このようにして、ディスコティック液晶性化合物が垂直かつねじれて配向している光学的異方性層を形成し、光学補償シートを作成した。
配向膜のラビング軸に対して４５゜の角度で、透明支持体側から光学補償シートに偏光を入射し、光学機器（Multi Chanel Photo Analyzer、大塚電子（株）製）を用いて出射光の偏光解析を行い、ツイスト角を求めたところ、２３０〜２５０゜であった。
【００９２】
別に、光学的異方性層塗布液からディスコティック液晶性化合物（２）を除いた以外は同様にして、ディスコティック液晶性化合物が実質的に垂直に配向しているが、ねじれていない光学補償シートを作成した。このシートについて、エリプソメーターを用いて、面内レターデーション（Ｒｅ）を測定し、その角度依存性から平均傾斜角を求めたところ、７０〜８５゜であった。
さらに別に、水平配向膜を用いてアンチパラレルセルを作成し、セル内に上記のディスコティック液晶性化合物（１）および（２）を封入した。得られた液晶セルについて、エリプソメーターを用いて、面内レターデーション（Ｒｅ）を測定し、その値をセルの厚みで割ることによりΔｎを求めたところ、０．０７であった。
【００９３】
［実施例２］
ポリイミド（ＰＩ１）に代えて、ポリイミド（ＰＩ５）を同量用いた以外は、実施例１と同様に光学補償シートを作成して評価した。ディスコティック液晶性化合物の平均傾斜角は、７５゜であった。
【００９４】
［実施例３］
ポリイミド（ＰＩ１）に代えて、ポリイミド（ＰＩ１０）を同量用いた以外は、実施例１と同様に光学補償シートを作成して評価した。ディスコティック液晶性化合物の平均傾斜角は、７０゜であった。
【００９５】
［実施例４］
ポリイミド（ＰＩ１）に代えて、ポリイミド（ＰＩ１３）を同量用いた以外は、実施例１と同様に光学補償シートを作成して評価した。ディスコティック液晶性化合物の平均傾斜角は、７５゜であった。
【００９６】
［比較例１］
無機垂直配向膜形成材料（ＥＸＰ−ＯＡ００４、日産化学工業（株）製）をメタノールで希釈し、固形分を２重量％とした。これをガラス板上に０．４μｍとなるようにバーコーターで塗布し、１４０℃で１０分間乾燥して、配向膜を形成した。
配向膜をラビングした後、アンチパラセルを二つ作成した。一方のセルには、棒状液晶性分子（ＭＢＢＡ）を挿入した。他方のセルには、実施例１で用いた光学的異方性層塗布液からメチルエチルケトンを蒸発させて固めたもの（ディスコティック液晶性分子）を挿入した。
それぞれのセルについて、液晶性分子の配向状態を調べた。棒状液晶性分子を挿入したセルでは、棒状液晶性分子がガラス板に垂直な方向にネマチック配向していた。これに対して、ディスコティック液晶性分子を挿入したセルでは、平均傾斜角が３０゜であり、垂直配向（５０〜９０゜）にはならなかった。
使用した無機垂直配向膜形成材料は、棒状液晶性分子用の垂直配向膜として市販されており、最も普通に使用されている。他の市販の棒状液晶性分子用垂直配向膜を用いた実験結果から、市販の棒状液晶性分子用垂直配向膜は、ディスコティック液晶性分子を垂直に配向させる機能が不充分であることが判明した。
【００９７】
［実施例５］
実施例１で作成した光学補償シートを用いて、図３の（ｅ）に示す構造のＳＴＮ型液晶表示装置を作成した。液晶セルと光学補償シートとが接する面で、液晶セルの棒状液晶性分子の配向方向と光学補償シートのディスコティック液晶性分子の配向方向とを一致させた。出射側偏光板の吸収軸と液晶セルの出射側の棒状液晶性分子の配向方向との角度は、４５゜に調節した。入射側偏光板の吸収軸と出射側偏光板の吸収軸とは直交するように配置した。
得られたＳＴＮ型液晶表示装置に電圧を印加したところ、ノーマリーブラックモードになった。視覚特性を測定したところ、コントラスト比が５以上の角度範囲が左右で１２０゜以上、上下で１５０゜以上得られた。
【図面の簡単な説明】
【図１】ＳＴＮ型液晶表示装置の電圧無印加（ｏｆｆ）の画素部分における液晶セル内の棒状液晶性分子の配向状態と光学的異方性層内のディスコティック液晶性分子の配向状態とを模式的に示す断面図である。
【図２】液晶セルの棒状液晶性分子と、それを光学補償する関係にある光学補償シートのディスコティック液晶性分子について、それぞれの屈折率楕円体を示す模式図である。
【図３】ＳＴＮ型液晶表示装置の層構成を示す模式図である。
【図４】ＳＴＮ型液晶表示装置の各要素について、好ましい光学的方向を示す平面図である。
【図５】ＳＴＮ型液晶表示装置の各要素について、別の好ましい光学的方向を示す平面図である。
【符号の説明】
１ 液晶セル
２、２ａ、２ｂ 光学補償シート
３、３ａ、３ｂ 偏光板
１１ 液晶セルの上基板
１２、１４ 液晶セルの配向膜
１３ 棒状液晶性分子の屈折率楕円体
１３ａ〜１３ｅ 棒状液晶性分子
１３ｔ 棒状液晶性分子層の厚み
１３ｘ、１３ｙ 棒状液晶性分子の配向膜に平行な面内の屈折率
１３ｚ 棒状液晶性分子の厚み方向の屈折率
１５ 液晶セルの下基板
２１ ディスコティック液晶性分子の屈折率楕円体
２１ａ〜２１ｅ ディスコティック液晶性分子
２１ｔ ディスコティック液晶性分子層の厚み
２１ｘ、２１ｙ ディスコティック液晶性分子の配向膜に平行な面内の屈折率
２１ｚ ディスコティック液晶性分子の厚み方向の屈折率
２２ 配向膜
２３ 透明支持体
ＢＬ バックライト
ＤＤａ、ＤＤｂ、ＤＤｃ、ＤＤｄ ディスコティック液晶性分子の円盤面の法線方向
ＲＤａ、ＲＤｂ 液晶セルの配向膜のラビング方向
ＴＡａ、ＴＡｂ 偏光板の透過軸
Ｘ 基準となる方向[0001]
[Industrial application fields]
The present invention relates to an optical compensation sheet having an optically anisotropic layer formed in this order from an alignment film and a discotic liquid crystalline molecule on a transparent support. The present invention also relates to an STN type liquid crystal display device. The present invention further relates to a method of aligning discotic liquid crystalline molecules with an average tilt angle in the range of 50 to 90 degrees.
[0002]
[Prior art]
The STN type liquid crystal display device includes an STN type liquid crystal cell, two polarizing plates, and one or two optical compensation sheets (retardation plates) provided between the STN type liquid crystal cell and the polarizing plate.
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. In the STN type liquid crystal cell, an alignment film for aligning rod-like liquid crystalline molecules is provided on two substrates. Further, the rod-like liquid crystalline molecules are twisted and aligned at 180 to 360 degrees using a chiral agent.
In an STN type liquid crystal display device without an optical compensation sheet, the display image is colored blue or yellow due to the birefringence of rod-like liquid crystal molecules. The coloring of the display image is inconvenient for both monochrome display and color display. The optical compensation sheet is used for eliminating such coloring and obtaining a bright and clear image. The optical compensation sheet may also be given a function of expanding the viewing angle of the liquid crystal cell. As the optical compensation sheet, a stretched birefringent film has been conventionally used. An optical compensation sheet for an STN type liquid crystal display device using a stretched birefringent film is described in JP-A-7-104284 and JP-A-7-13021.
[0003]
It has been proposed to use an optical compensation sheet having an optically anisotropic layer containing a discotic liquid crystalline molecule on a transparent support, instead of the optical compensation sheet made of a stretched birefringent film. The optically anisotropic layer is formed by aligning discotic liquid crystal molecules and fixing the alignment state. Discotic liquid crystalline molecules generally have a large birefringence. Discotic liquid crystal molecules have various alignment forms. By using discotic liquid crystalline molecules, it is possible to produce an optical compensation sheet having optical properties that cannot be obtained by a conventional stretched birefringent film. Optical compensation sheets using discotic liquid crystalline molecules are described in JP-A-6-214116, US Pat. Nos. 5,583,679, 5,646,703, and German Published Patent No. 3,911,620A1. However, these optical compensation sheets are designed assuming a TN type liquid crystal display device as a main application.
[0004]
It is conceivable to use an optical compensation sheet using discotic liquid crystal molecules in an STN type liquid crystal display device. In the STN type liquid crystal display device, rod-like liquid crystalline molecules that are super twisted to be larger than 90 ° are used in the birefringence mode. The STN type liquid crystal display device is characterized in that a large-capacity clear display is possible by time-division driving even with a simple matrix electrode structure without active elements (thin film transistors and diodes).
In order to optically compensate an STN type liquid crystal cell using discotic liquid crystal molecules, it is necessary to align the discotic liquid crystal molecules substantially vertically (homogeneous alignment). It is preferable that the discotic liquid crystalline molecules are further twisted. JP-A-9-26572 discloses an optical compensation sheet in which discotic liquid crystalline molecules are twisted and aligned. Furthermore, the drawing of this publication shows a state in which the discotic liquid crystal molecules are aligned substantially vertically.
[0005]
[Problems to be solved by the invention]
With the technique disclosed in Japanese Patent Application Laid-Open No. 9-26572, it is difficult to uniformly align (monodomain alignment) the discotic liquid crystalline molecules from the alignment film interface to the air interface. If the discotic liquid crystalline molecules are not uniformly oriented, light scattering due to disclination occurs, and the contrast ratio of the display image decreases. Research is also progressing on a technique for aligning rod-like liquid crystal molecules used in a liquid crystal cell substantially vertically (homeotropic alignment). For example, in a vertical alignment liquid crystal cell in which rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied, and substantially horizontally when voltage is applied, the rod-like liquid crystalline molecules are substantially aligned. An alignment film that is vertically aligned is required. Various alignment films have been proposed for rod-like liquid crystal molecules.
A rod-like liquid crystal molecule and a discotic liquid crystal molecule have completely different molecular structures and optical properties. As for the vertical alignment, discotic liquid crystalline molecules, unlike rod-shaped liquid crystalline molecules, need not only to be aligned vertically but also to align the disc surface of the discotic liquid crystalline molecules in a certain direction (the directionality is necessary). As a result of research conducted by the present inventor, most of the alignment films known as vertical alignment films of rod-like liquid crystalline molecules did not exhibit a function of aligning discotic liquid crystalline molecules in a vertical and uniform direction.
[0006]
An object of the present invention is to provide an optical compensation sheet particularly suitable for an STN type liquid crystal display device.
Another object of the present invention is to provide an STN type liquid crystal display device in which coloring of a display image is eliminated and a clear image with high contrast can be obtained.
Another object of the present invention is to provide a method for stably aligning discotic liquid crystalline molecules in a vertical and uniform direction.
[0007]
[Means for Solving the Problems]
  The present invention relates to an optical compensation sheet having an alignment film and an optically anisotropic layer formed of discotic liquid crystalline molecules in this order on a transparent support, the alignment film having an aromatic ring or aromatic group in the side chain. A polymer containing 2 to 4 family heterocycles,-O-, -O-CO-, -O-CO-NH-, -O-CO-NH-alkylene between the main chain of the polymer and the aromatic ring or aromatic heterocycle on the most main chain side Selected from the group consisting of the group-, -O-CO-NH-alkylene group -O-, -O-CO-NH-alkylene group -CO-O- and -O-CO-NH-alkylene group -CO-NH-. Connected via a connecting group (the left side is bonded to the main chain and the right side is bonded to the most aromatic ring or aromatic heterocycle on the main chain side),The optical compensation sheet is characterized in that the discotic liquid crystalline molecules are aligned with an average inclination angle in the range of 50 to 90 degrees.
[0008]
Preferred embodiments of the optical compensation sheet of the present invention are as follows.
(1) An optical compensation sheet characterized in that the polymer main chain has a polyimide structure.
(2) The optical compensation sheet, wherein the polymer has a biphenyl structure in at least one of the main chain and the side chain.
(3) An optical compensation sheet in which the discotic liquid crystalline molecules are twisted and the twist angle is in the range of 90 to 360 degrees.
[0009]
  The present invention also provides an STN type liquid crystal cell, two polarizing plates disposed on both sides thereof, and one or two optical compensation sheets disposed between the STN type liquid crystal cell and one or both polarizing plates. STN-type liquid crystal display device comprising: an optical compensation sheet having an optically anisotropic layer formed of a transparent support, an alignment film, and a discotic liquid crystalline molecule in this order from the polarizing plate side. Including a polymer containing 2 to 4 aromatic rings or aromatic heterocyclic rings in the side chain,-O-, -O-CO-, -O-CO-NH-, -O-CO-NH-alkylene between the main chain of the polymer and the aromatic ring or aromatic heterocycle on the most main chain side Selected from the group consisting of the group-, -O-CO-NH-alkylene group -O-, -O-CO-NH-alkylene group -CO-O- and -O-CO-NH-alkylene group -CO-NH-. Via a linking group (the left side is bonded to the main chain and the right side is bonded to the most aromatic ring or aromatic heterocycle on the main chain side),An STN type liquid crystal display device characterized in that the discotic liquid crystal molecules are aligned with an average tilt angle in the range of 50 to 90 degrees, twisted, and the twist angle is in the range of 90 to 360 degrees. is there.
[0010]
  The present invention further includes a polymer containing 2 to 4 aromatic rings or aromatic heterocyclic rings in the side chain.Between the main chain of the polymer and the aromatic ring or aromatic heterocycle on the most main chain side is -O-, -O-CO-, -O-CO-NH-, -O-CO-NH A group consisting of -alkylene group-, -O-CO-NH-alkylene group -O-, -O-CO-NH-alkylene group -CO-O- and -O-CO-NH-alkylene group -CO-NH- Linked via a linking group selected from the above (the left side is bonded to the main chain, and the right side is bonded to the most aromatic ring or aromatic heterocycle on the main chain side)There is also a method of aligning discotic liquid crystalline molecules with an average tilt angle in the range of 50 to 90 degrees using an alignment film.
[0011]
In the present specification, the average tilt angle of the discotic liquid crystal molecules means the average angle between the disc surface of the discotic liquid crystal molecules and the surface of the support (or the surface of the alignment film). A state in which the discotic liquid crystal molecules are aligned with an average inclination angle in the range of 50 to 90 degrees is referred to as the discotic liquid crystal molecules being aligned substantially vertically.
[0012]
【The invention's effect】
As a result of research, the inventor of the present invention uses a polymer containing two, three or four aromatic rings or aromatic heterocycles in the side chain as an alignment film, so that the discotic liquid crystal molecules are substantially vertical and Succeeded in stable orientation in a uniform direction. By obtaining means for stably aligning the discotic liquid crystalline molecules in a substantially vertical and uniform direction, an optical compensation sheet suitable for an STN type liquid crystal display device can be produced. By using an optical compensation sheet in which discotic liquid crystal molecules are aligned substantially vertically (preferably further twisted), coloring of the display image of the STN type liquid crystal display device is eliminated, and a high contrast clearness is achieved. Can be obtained.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the alignment state of rod-like liquid crystal molecules in a liquid crystal cell and the alignment state of discotic liquid crystal molecules in an optically anisotropic layer in a pixel portion where no voltage is applied (off) in an STN type liquid crystal display device. It is sectional drawing shown typically.
As shown in FIG. 1, the liquid crystal cell has a rod-like liquid crystal molecule (13a) between the lower alignment film (12) of the upper substrate (11) and the upper alignment film (14) of the lower substrate (15). To e). Due to the functions of the alignment films (12, 14) and the chiral agent added to the liquid crystal layer, the rod-like liquid crystal molecules (13a to 13e) are twisted and aligned as shown in FIG.
Although omitted in FIG. 1, each of the upper substrate (11) and the lower substrate (15) of the liquid crystal cell has an electrode layer. The electrode layer has a function of applying a voltage to the rod-like liquid crystal molecules (13a to e).
When the applied voltage of the STN type liquid crystal cell is 0 (when no voltage is applied), as shown in FIG. 1, the rod-like liquid crystal molecules (13a to 13e) are substantially parallel to the plane of the alignment films (12, 14) ( Oriented horizontally). The rod-like liquid crystal molecules (13a to 13e) are oriented in a direction in which they are twisted along the thickness direction and spiral in a horizontal plane (in FIG. 1, approximately 240 ° counterclockwise from 13a to 13e). ing.
When voltage is applied to the STN type liquid crystal cell (on), the rod-like liquid crystal molecules (13b to 13d) in the central portion of the liquid crystal cell are aligned more vertically (electric field) than when no voltage is applied (off). Rearrange parallel to the direction). The alignment state of the rod-like liquid crystalline molecules (13a, 13e) in the vicinity of the alignment films (12, 14) does not substantially change even when a voltage is applied.
[0014]
An optical compensation sheet is disposed below the liquid crystal cell. The optical compensation sheet shown in FIG. 1 has an alignment film (22) and an optically anisotropic layer in this order on a transparent support (23). The optically anisotropic layer is a layer obtained by aligning discotic liquid crystal molecules (21a to 21e) and fixing the molecules in the alignment state.
In the present invention, as shown in FIG. 1, the disc surfaces of the discotic liquid crystal molecules (21a to 21e) are aligned substantially perpendicularly to the surface of the alignment film (22). As shown in FIG. 1, the discotic liquid crystalline molecules (21a to 21e) are spiraled in the horizontal plane while twisting along the thickness direction (in FIG. 1, approximately 240 ° clockwise from 21a to 21e). ) In such a direction.
In FIG. 1, rod-like liquid crystal molecules and discotic liquid crystal molecules have a relationship in which 13a and 21e, 13b and 21d, 13c and 21c, 13d and 21b, and 13e and 21a correspond to each other. That is, the discotic liquid crystalline molecules 21e are optically compensated for the rod-like liquid crystalline molecules 13a, and similarly, the discotic liquid crystalline molecules 21a are optically compensated for the rod-like liquid crystalline molecules 13e. Each correspondence will be described with reference to FIG.
[0015]
FIG. 2 is a schematic diagram showing refractive index ellipsoids of rod-like liquid crystalline molecules of a liquid crystal cell and discotic liquid crystalline molecules of an optical compensation sheet in a relationship for optical compensation thereof.
The refractive index ellipsoid (13) of rod-like liquid crystalline molecules of the liquid crystal cell is formed by an in-plane refractive index (13x, 13y) parallel to the alignment film and a refractive index (13z) in the thickness direction of the liquid crystal cell. In the STN type liquid crystal cell, the refractive index (13x) in one direction in the plane parallel to the alignment film has a large value, the refractive index (13y) in the plane perpendicular to it and the refractive index in the thickness direction of the liquid crystal cell ( 13z) is a small value. Therefore, the refractive index ellipsoid (13) has a shape in which a rugby ball is laid sideways as shown in FIG. In such a liquid crystal cell having a refractive index ellipsoid that is not spherical, an angle dependency occurs in the birefringence. This angle dependency is eliminated by using an optical compensation sheet.
[0016]
The refractive index ellipsoid (21) of the discotic liquid crystalline molecules of the optical compensation sheet having the relationship of optically compensating the rod-like liquid crystalline molecules is also different from the refractive index (21x, 21y) in the plane parallel to the alignment film. It is formed by the refractive index (21z) in the thickness direction of the isotropic layer. In the present invention, by aligning the discotic liquid crystalline molecules substantially perpendicularly, the refractive index (21x) in one direction in the plane parallel to the alignment film becomes a small value, and the in-plane refraction in the direction perpendicular to it. The refractive index (21z) and the refractive index (21z) in the thickness direction of the optically anisotropic layer are large values. Therefore, the refractive index ellipsoid (21) has a shape in which a disk as shown in FIG.
From the above relationship, the retardation generated in the liquid crystal cell (1) can be offset by the optical compensation sheet (2). That is, the refractive index (13x, 13y, 13z) of the rod-like liquid crystalline molecule, the refractive index (21x, 21y, 21z) of the discotic liquid crystalline molecule, and the thickness (13t) of the rod-like liquid crystalline molecule layer having the same director direction If the liquid crystal display device is designed so that the thickness (21t) of the discotic liquid crystalline molecular layer satisfies the following formula, the angle dependence of the liquid crystal cell can be eliminated.
│ (13x-13y) x 13t│ = │ (21x-21y) x 21t││ (13x-13z) x 13t│ = │ (21x-21z) x 21t│
[0017]
FIG. 3 is a schematic diagram showing a layer structure of the STN type liquid crystal display device.
The liquid crystal display device shown in FIG. 3A has a lower polarizing plate (3a), a lower optical compensation sheet (2a), an STN type liquid crystal cell (1), and an upper polarizing plate (in order from the backlight (BL) side). 3b).
The liquid crystal display device shown in FIG. 3B has a lower polarizing plate (3a), a lower optical compensation sheet (2a), an upper optical compensation sheet (2b), an STN type liquid crystal cell (in order from the backlight (BL) side). 1) and the upper polarizing plate (3b).
The liquid crystal display device shown in (c) of FIG. 3 includes, in order from the backlight (BL) side, a lower polarizing plate (3a), an STN type liquid crystal cell (1), an upper optical compensation sheet (2b), and an upper polarizing plate ( 3b).
The liquid crystal display device shown in FIG. 3D has a lower polarizing plate (3a), an STN liquid crystal cell (1), a lower optical compensation sheet (2a), an upper optical compensation sheet (in order from the backlight (BL) side). 2b) and the upper polarizing plate (3b).
The liquid crystal display device shown in FIG. 3E has a lower polarizing plate (3a), a lower optical compensation sheet (2a), an STN liquid crystal cell (1), an upper optical compensation sheet (in order from the backlight (BL) side). 2b) and the upper polarizing plate (3b).
[0018]
In FIG. 3, the transmission axis (TAa) of the lower polarizing plate (3a) and the normal (director) direction (DDa) of the disc surface of the discotic liquid crystalline molecules in the vicinity of the alignment film of the lower optical compensation sheet (2a) are shown as arrows. ), Normal (director) direction (DDb) of the disc surface of the discotic liquid crystalline molecules in the vicinity of the liquid crystal cell of the lower optical compensation sheet (2a), rubbing direction (RDa) of the lower alignment film of the liquid crystal cell (1), liquid crystal The rubbing direction (RDb) of the upper alignment film of the cell (1), the normal (director) direction (DDc) of the disc surface of the discotic liquid crystalline molecules in the vicinity of the liquid crystal cell of the upper optical compensation sheet (2a), the upper optical compensation sheet The normal (director) direction (DDd) of the disc surface of the discotic liquid crystalline molecules in the vicinity of the alignment film (2a) and the transmission axis (TAb) of the upper polarizing plate (3b) are shown. The exact angle of each will be described in FIGS.
[0019]
FIG. 4 is a plan view showing a preferable optical direction for each element of the STN type liquid crystal display device. FIG. 4 shows an arrangement that emphasizes front contrast.
FIG. 4A shows a case where one optical compensation sheet is provided between the lower polarizing plate and the STN type liquid crystal cell, as shown in FIG.
FIG. 4B shows a case where two optical compensation sheets are provided between the lower polarizing plate and the STN type liquid crystal cell as shown in FIG.
FIG. 4C shows a case where one optical compensation sheet is provided between the STN type liquid crystal cell and the upper polarizing plate, as shown in FIG.
FIG. 4D shows a case where two optical compensation sheets are provided between the STN type liquid crystal cell and the upper polarizing plate, as shown in FIG.
4 (e) shows an optical compensation sheet between the lower polarizing plate and the STN type liquid crystal cell and between the STN type liquid crystal cell and the upper polarizing plate, as shown in FIG. This is a case where there are two optical compensation sheets in total.
X is a direction serving as a reference (0 °), and the meaning of each arrow is as described in FIG. Note that the transmission axis (TAa) of the lower polarizing plate and the transmission axis (TAb) of the upper polarizing plate may be interchanged.
[0020]
FIG. 5 is a plan view showing another preferable optical direction for each element of the STN type liquid crystal display device. FIG. 5 shows an arrangement that emphasizes color.
FIG. 5A shows a case where one optical compensation sheet is provided between the lower polarizing plate and the STN type liquid crystal cell, as shown in FIG.
FIG. 5B shows a case where two optical compensation sheets are provided between the lower polarizing plate and the STN type liquid crystal cell, as shown in FIG.
FIG. 5C shows a case where one optical compensation sheet is provided between the STN type liquid crystal cell and the upper polarizing plate, as shown in FIG.
FIG. 5D shows a case where two optical compensation sheets are provided between the STN type liquid crystal cell and the upper polarizing plate, as shown in FIG.
FIG. 5 (e) shows an optical compensation sheet between the lower polarizing plate and the STN type liquid crystal cell and between the STN type liquid crystal cell and the upper polarizing plate, as shown in FIG. This is a case where there are two optical compensation sheets in total.
X is a direction serving as a reference (0 °), and the meaning of each arrow is as described in FIG. Note that the transmission axis (TAa) of the lower polarizing plate and the transmission axis (TAb) of the upper polarizing plate may be interchanged.
[0021]
[Transparent support]
As the transparent support of the optical compensation sheet, it is preferable to use a polymer film having a small optical anisotropy. That the support is transparent means that the light transmittance is 80% or more. Specifically, the small optical anisotropy means that the in-plane retardation (Re) is preferably 20 nm or less, more preferably 10 nm or less, and most preferably 5 nm or less. The thickness direction retardation (Rth) is preferably 100 nm or less, more preferably 50 nm or less, and most preferably 30 nm or less. In-plane retardation (Re) and thickness direction retardation (Rth) are respectively defined by the following formulas.
Re = (nx−ny) × d
Rth = [{(nx + ny) / 2} -nz] × d
In the formula, nx and ny are in-plane refractive indexes of the transparent support, nz is the refractive index in the thickness direction of the transparent support, and d is the thickness of the transparent support.
[0022]
Examples of the polymer include cellulose ester, polycarbonate, polysulfone, polyethersulfone, polyacrylate and polymethacrylate. Cellulose esters are preferred, acetyl cellulose is more preferred, and triacetyl cellulose is most preferred. The polymer film is preferably formed by a solvent cast method.
The thickness of the transparent support is preferably 20 to 500 μm, and more preferably 50 to 200 μm.
In order to improve adhesion between the transparent support and the layer (adhesive layer, vertical alignment film or optically anisotropic layer) provided thereon, surface treatment (eg, glow discharge treatment, corona discharge treatment, Ultraviolet (UV) treatment, flame treatment) may be performed. An adhesive layer (undercoat layer) may be provided on the transparent support.
[0023]
[Alignment film]
According to the study by the present inventors, in order to align the discotic liquid crystalline molecules substantially vertically, the function of the side chain is more important than the main chain of the polymer contained in the alignment film. Specifically, the surface energy of the alignment film is lowered by the functional group of the polymer, thereby bringing the discotic liquid crystalline molecules into an upright state. An aromatic ring or an aromatic heterocyclic ring is effective as the functional group for reducing the surface energy of the alignment film. In order to make an aromatic ring or an aromatic heterocyclic ring exist on the surface of the alignment film, an aromatic ring or an aromatic heterocyclic ring is introduced into the side chain of the polymer. The aromatic ring or aromatic heterocyclic ring may be introduced not only into the side chain of the polymer but also into the main chain.
The number of aromatic rings or aromatic heterocycles contained in the side chain (or side chain and main chain) is 2 to 4 (in the case of side chain and main chain, respectively), and is 2 or 3. 2 is particularly preferable.
Examples of the aromatic ring include benzene ring, indene ring, naphthalene ring, azulene ring, fluorene ring, phenanthrene ring, anthracene ring, acenaphthylene ring, biphenylene ring, naphthacene ring, triphenylene ring and pyrene ring. Aromatic heterocycles are generally 5- or 6-membered unsaturated heterocycles. The heterocyclic ring preferably contains the most double bond. Examples of aromatic heterocycle include furan ring, thiophene ring, pyrrole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, imidazole ring, pyrazole ring, furazane ring, pyran ring, pyridine ring, pyridazine ring , Pyrimidine ring and pyrazine ring.
An aromatic ring is preferable to an aromatic heterocyclic ring, and a benzene ring is particularly preferable. The aromatic ring and the aromatic heterocyclic ring may have a substituent. Examples of the substituent include a halogen atom (F, Cl, Br), carboxyl, cyano, an alkyl group, a cycloalkyl group, and an alkoxy group.
The alkyl group may have a branch. The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 15 carbon atoms, still more preferably 1 to 10 carbon atoms, and most preferably 1 to 6 carbon atoms.
The cycloalkyl group is preferably cyclohexyl.
The alkoxy group may have a branch. The alkoxy group preferably has 1 to 20 carbon atoms, more preferably 1 to 15 carbon atoms, still more preferably 1 to 10 carbon atoms, and most preferably 1 to 6 carbon atoms.
[0024]
The main chain and the aromatic ring or aromatic heterocyclic ring closest to the main chain are preferably connected via a connecting group without being directly connected. Examples of the linking group include -O-, -O-CO-, -O-CO-NH-, -O-CO-NH-alkylene group-, -O-CO-NH-alkylene group -O-,- O—CO—NH-alkylene group —CO—O— and —O—CO—NH-alkylene group —CO—NH— are included (the left side is bonded to the main chain and the right side is the most aromatic ring on the main chain side) Or bonded to an aromatic heterocycle).
The alkylene group may have a branched or cyclic structure. The alkylene group preferably has 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, still more preferably 1 to 15 carbon atoms, and most preferably 1 to 12 carbon atoms.
It is preferable that at least two aromatic rings or aromatic heterocycles are directly connected by a single bond. It is preferable that at least two benzene rings are directly connected by a single bond. As such a structure, a biphenyl structure is most preferable.
[0025]
The main chain of the polymer preferably has a polyimide structure. Polyimide is generally synthesized by a condensation reaction of tetracarboxylic acid and diamine. A polyimide corresponding to a copolymer may be synthesized using two or more kinds of tetracarboxylic acids or two or more kinds of diamines. The aromatic ring or aromatic heterocyclic ring may be present in the repeating unit derived from tetracarboxylic acid, may be present in the repeating unit derived from diamine, or may be present in both repeating units.
[0026]
A polymerizable group may be introduced into the polymer of the alignment film. When a polymer having a polymerizable group and a discotic liquid crystalline molecule having a polymerizable group are used in combination, the polymer and the discotic liquid crystalline molecule are chemically bonded via the interface between the optically anisotropic layer and the alignment film. Can be combined. Thereby, the durability of the optical compensation sheet can be improved.
When the main chain of the polymer has a polyimide structure, the polymerizable group is present in both the repeating unit derived from the tetracarboxylic acid, the repeating unit derived from the diamine, or present in both repeating units. May be.
The type of the polymerizable group is determined according to the type of the polymerizable group (Q) of the discotic liquid crystal molecule described later. As described later, the polymerizable group (Q) of the liquid crystal molecule is preferably an unsaturated polymerizable group (examples Q1 to Q7 described later), an epoxy group (Q8) or an aziridinyl group (Q9). A saturated polymerizable group is more preferable, and an ethylenically unsaturated polymerizable group (Q1 to Q6) is most preferable. Similarly, the polymerizable group of the polymer of the alignment film is preferably an unsaturated polymerizable group, an epoxy group or an aziridinyl group, more preferably an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group. Most preferred.
[0027]
The main chain of the polymer and the polymerizable group are preferably linked via a linking group without being directly linked. Examples of the linking group include -O-, -O-CO-, -O-CO-NH-, -O-CO-NH-alkylene group-, -O-CO-NH-alkylene group -O-,- O-CO-NH-alkylene group -CO-O-, -O-CO-NH-alkylene group -O-CO-, -O-CO-NH-alkylene group -CO-NH-, -O-CO-alkylene -O-CO-, -O-CO-arylene group -O-alkylene group -O-CO-, -O-CO-arylene group -O-alkylene group -O-, -O-CO-arylene group -O -Alkylene group- and -O-alkylene group -O-CO- are included (the left side is bonded to the main chain and the right side is bonded to the polymerizable group).
The alkylene group may have a branched or cyclic structure. The alkylene group preferably has 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, still more preferably 1 to 15 carbon atoms, and most preferably 1 to 12 carbon atoms.
The arylene group is preferably phenylene or naphthylene, more preferably phenylene, and most preferably p-phenylene. The arylene group may have a substituent.
The polymer may have two or more polymerizable groups.
[0028]
Examples of repeating units derived from tetracarboxylic acid (the nitrogen atom of the imide structure is derived from diamine) are shown below.
[0029]
[Chemical 1]

[0030]
[Chemical formula 2]

[0031]
[Chemical Formula 3]

[0032]
[Formula 4]

[0033]
Examples of repeating units derived from diamine are shown below.
[0034]
[Chemical formula 5]

[0035]
[Chemical 6]

[0036]
[Chemical 7]

[0037]
[Chemical 8]

[0038]
[Chemical 9]

[0039]
Embedded image

[0040]
Embedded image

[0041]
Embedded image

[0042]
A group different from the repeating unit may be bonded to the end of the polyimide. Examples of the end group (E) are shown below.
[0043]
Embedded image

[0044]
Examples of a polyimide having a hydrocarbon group in the side chain that can be preferably used for the alignment film and a polyimide having a hydrocarbon group in the main chain and the side chain include a repeating unit (A) derived from a tetracarboxylic acid, The numbers of the repeating unit (B) and terminal group (E) are shown with reference. The proportion of repeating units in the copolymer is mol%.
[0045]
PI1: -A1-B1-
PI2:-(A1-B1)₈₀-(A1-B2)₂₀−
PI3: -A2-B4-
PI4: -A3-B4-
PI5 :-( A4-B11)₉₀-(A4-B21)_Ten−
PI6 :-( A4-B11)₈₀-(A4-B21)₂₀−
PI7:-(A4-B11)₇₀-(A4-B21)₃₀−
PI8: -A4-B11-
PI9: -A5-B32-
PI10: -A7-B23-
PI11: -A8-B1-
PI12: -A8-B6-
PI13: -A9-B12-
PI14: -A10-B18-
PI15: -A11-B22-
PI16: -A12-B27-
[0046]
PI17: E2- (A1-B1) -E5
PI18: E4- (A7-B21) -E8
[0047]
PI19:-(A8-B21)₈₀-(A14-B21)₂₀−
PI20:-(A8-B21)₉₀-(A15-B21)_Ten−
PI21 :-( A8-B21)₉₀-(A8-B59)_Ten−
[0048]
A polyamic acid containing a hydrocarbon group having 12 or more carbon atoms can also be used for the alignment film. The polyamic acid is synthesized by a partial condensation reaction between tetracarboxylic acid and diamine. That is, two of the four carboxyls of tetracarboxylic acid are reacted with diamine to form an amide bond. The remaining two carboxyls of the tetracarboxylic acid remain in the polyamic acid.
Even a polyamic acid can function as an alignment film. Moreover, after heating polyamic acid and carrying out dehydration ring closure to make it a polyimide, it can also be utilized as an alignment film. The polyamic acid may be partially dehydrated and closed by heating in a short time or at a low temperature, and the resulting copolymer of polyamic acid and polyimide may be used as the alignment film.
[0049]
The polymerization degree of the polymer used for the alignment film is preferably 200 to 5000, and more preferably 300 to 3000. The molecular weight of the polymer is preferably 9000 to 200000, more preferably 13000 to 130,000.
Two or more kinds of polymers may be used in combination.
[0050]
The polymer used for the alignment film may be crosslinked. The cross-linking reaction is preferably performed simultaneously with or after the application of the alignment layer coating solution.
Crosslinking of the polymer can be formed using a crosslinking agent. Examples of crosslinking agents include epoxy compounds (eg, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, polyethylene glycol diglycidyl ether), aldehydes (eg, formaldehyde, glyoxal, glutaraldehyde, malonaldehyde, phthalaldehyde, terephthalaldehyde, Succinaldehyde, isophthalaldehyde, dialdehyde starch), N-methylol compounds (eg, dimethylolurea, methyloldimethylhydantoin), dioxane (eg, 2,3-dihydroxydioxane), carbenium, 2-naphthalate sulfonate, 1, 1-bispyrrolidino-1-chloropyridinium, 1-morpholinocarbonyl-3- (sulfonatoaminomethyl), active vinyl compound (eg, 1,3,5-tria) Liloyl-hexahydro-s-triazine, bis (vinylsulfone) methane, N, N′-methylenebis- [β- (vinylsulfonyl) propionamide), active halogen compounds (eg, 2,4-dichloro-6-hydroxy-s -Triazines) and isoxazoles. When the polymer is polyimide or polyamic acid, it is preferable to use an epoxy compound as a crosslinking agent.
[0051]
The thickness of the alignment film is preferably 0.1 to 10 μm.
In the formation of the alignment film, it is preferable to perform a rubbing treatment. The rubbing treatment is performed by rubbing the surface of the film containing the polymer several times in a certain direction with paper or cloth.
In addition, after the discotic liquid crystalline molecules are aligned substantially vertically using the alignment film, the optically anisotropic layer is formed by fixing the discotic liquid crystalline molecules while maintaining the alignment state. Only the isotropic layer may be transferred onto the transparent support. The discotic liquid crystal molecules having the fixed alignment state can maintain the alignment state even without the alignment film.
[0052]
[Optically anisotropic layer]
The optically anisotropic layer contains discotic liquid crystalline molecules.
In the optically anisotropic layer, the above-described alignment film is used to align the disc surface of the discotic liquid crystalline molecules substantially perpendicular to the alignment film (average inclination angle in the range of 50 to 90 degrees). Let The discotic liquid crystalline molecules are preferably fixed in the optically anisotropic layer while maintaining a vertical (homogeneous) alignment state. More preferably, the discotic liquid crystalline molecules are fixed by a polymerization reaction.
Discotic liquid crystalline molecules are described in various literature (C. Destrade et al., Mol. Crysr. Liq. Cryst., Vol. 71, page 111 (1981); edited by the Chemical Society of Japan, Quarterly Review, No. 22, 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)). The polymerization of discotic liquid crystalline molecules is described in JP-A-8-27284.
In order to fix the discotic liquid crystalline molecules by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline molecules. However, when the polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain the orientation state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Accordingly, the discotic liquid crystalline molecule having a polymerizable group is preferably a compound represented by the following formula.
[0053]
D (-LQ)_n
Where D is a discotic core; L is a divalent linking group; Q is a polymerizable group; and n is an integer from 4 to 12.
Examples of the disk-shaped core (D) of the above formula are 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).
[0054]
Embedded image

[0055]
Embedded image

[0056]
Embedded image

[0057]
Embedded image

[0058]
Embedded image

[0059]
Embedded image

[0060]
Embedded image

[0061]
In the above formula, the divalent linking group (L) is a divalent group selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. The linking group is preferably. The divalent linking group (L) is a combination of at least two divalent groups selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, and —S—. More preferably, it is a group. The divalent linking group (L) is most preferably a group obtained by combining at least two divalent groups selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, -CO- and -O-. 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. The alkylene group, alkenylene group and arylene group may have a substituent (eg, alkyl group, halogen atom, cyano, alkoxy group, acyloxy group).
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.
[0062]
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-
L11: -O-AL-
L12: -O-AL-O-
L13: -O-AL-O-CO-
[0063]
L14: -O-AL-O-CO-NH-AL-
L15: -O-AL-S-AL-
L16: -O-CO-AL-AR-O-AL-O-CO-
L17: -O-CO-AR-O-AL-CO-
L18: -O-CO-AR-O-AL-O-CO-
L19: -O-CO-AR-O-AL-O-AL-O-CO-
L20: -O-CO-AR-O-AL-O-AL-O-AL-O-CO-
L21: -S-AL-
L22: -S-AL-O-
L23: -S-AL-O-CO-
L24: -S-AL-S-AL-
L25: -S-AR-AL-
[0064]
When an asymmetric carbon atom is introduced into AL (an alkylene group or an alkenylene group), the discotic liquid crystalline molecules can be twisted and aligned in a spiral shape. Examples of AL * containing an asymmetric carbon atom are listed below. The left side is the disk-shaped core (D) side, and the right side is the polymerizable group (Q) side. The carbon atom (C) marked with * is an asymmetric carbon atom. The optical activity may be either S or R.
[0065]
AL * 1: -CH₂CH₂-C * HCH_Three-CH₂CH₂CH₂−
AL * 2: -CH₂CH₂CH₂-C * HCH_Three-CH₂CH₂−
AL * 3: -CH₂-C * HCH_Three-CH₂CH₂CH₂CH₂−
AL * 4: -C * HCH_Three-CH₂CH₂CH₂CH₂CH₂−
AL * 5: -CH₂CH₂CH₂CH₂-C * HCH_Three-CH₂−
AL * 6: -CH₂CH₂CH₂CH₂CH₂-C * HCH_Three−
AL * 7: -C * HCH_Three-CH₂CH₂CH₂CH₂−
AL * 8: -CH₂-C * HCH_Three-CH₂CH₂CH₂−
AL * 9: -CH₂CH₂-C * HCH_Three-CH₂CH₂−
AL * 10: -CH₂CH₂CH₂-C * HCH_Three-CH₂−
AL * 11: -CH₂CH₂CH₂CH₂-C * HCH_Three−
AL * 12: -C * HCH_Three-CH₂CH₂CH₂−
AL * 13: -CH₂-C * HCH_Three-CH₂CH₂−
AL * 14: -CH₂CH₂-C * HCH_Three-CH₂−
AL * 15: -CH₂CH₂CH₂-C * HCH_Three−
[0066]
AL * 16: -CH₂-C * HCH_Three−
AL * 17: -C * HCH_Three-CH₂−
AL * 18: -C * HCH_Three-CH₂CH₂CH₂CH₂CH₂CH₂−
AL * 19: -CH₂-C * HCH_Three-CH₂CH₂CH₂CH₂CH₂−
AL * 20: -CH₂CH₂-C * HCH_Three-CH₂CH₂CH₂CH₂−
AL * 21: -CH₂CH₂CH₂-C * HCH_Three-CH₂CH₂CH₂−
AL * 22: -C * HCH_Three-CH₂CH₂CH₂CH₂CH₂CH₂CH₂−
AL * 23: -CH₂-C * HCH_Three-CH₂CH₂CH₂CH₂CH₂CH₂−
AL * 24: -CH₂CH₂-C * HCH_Three-CH₂CH₂CH₂CH₂CH₂−
AL * 25: -CH₂CH₂CH₂-C * HCH_Three-CH₂CH₂CH₂CH₂−
AL * 26: -C * HCH_Three-(CH₂)₈−
AL * 27: -CH₂-C * HCH_Three-(CH₂)₈−
AL * 28: -CH₂-C * HCH₂CH_Three−
AL * 29: -CH₂-C * HCH₂CH_Three-CH₂−
AL * 30: -CH₂-C * HCH₂CH_Three-CH₂CH₂−
[0067]
AL * 31: -CH₂-C * HCH₂CH_Three-CH₂CH₂CH₂CH₂−
AL * 32: -CH₂-C * H (n-C_ThreeH₇) -CH₂CH₂−
AL * 33: -CH₂-C * H (n-C_ThreeH₇) -CH₂CH₂CH₂CH₂−
AL * 34: -CH₂-C * H (OCOCH_Three) -CH₂CH₂−
AL * 35: -CH₂-C * H (OCOCH_Three) -CH₂CH₂CH₂CH₂−
AL * 36: -CH₂-C * HF-CH₂CH₂−
AL * 37: -CH₂-C * HF-CH₂CH₂CH₂CH₂−
AL * 38: -CH₂-C * HCl-CH₂CH₂−
AL * 39: -CH₂-C * HCl-CH₂CH₂CH₂CH₂−
AL * 40: -CH₂-C * HOCH_Three-CH₂CH₂−
AL * 41: -CH₂-C * HOCH_Three-CH₂CH₂CH₂CH₂−
AL * 42: -CH₂-C * HCN-CH₂CH₂−
AL * 43: -CH₂-C * HCN-CH₂CH₂CH₂CH₂−
AL * 44: -CH₂-C * HCF_Three-CH₂CH₂−
AL * 45: -CH₂-C * HCF_Three-CH₂CH₂CH₂CH₂−
[0068]
The polymerizable group (Q) of the above formula is determined according to the type of polymerization reaction. Examples of the polymerizable group (Q) are shown below.
[0069]
Embedded image

[0070]
The polymerizable group (Q) is preferably an unsaturated polymerizable group (Q1 to Q7), an epoxy group (Q8) or an aziridinyl group (Q9), more preferably an unsaturated polymerizable group, and an ethylenic group. Most preferably, it is an unsaturated polymerizable group (Q1 to Q6).
In the above formula, n is an integer of 4 to 12. A specific number is determined according to the type of discotic core (D). In addition, although the combination of several L and Q may differ, it is preferable that it is the same.
Two or more kinds of discotic liquid crystal molecules may be used in combination. For example, a molecule having an asymmetric carbon atom in a divalent linking group and a molecule not having it can be used in combination. A molecule having a polymerizable group (Q) and a molecule not having the polymerizable group (Q) may be used in combination. It is particularly preferred to use in combination a molecule having an asymmetric carbon atom and having no polymerizable group and a molecule having a polymerizable group and not having an asymmetric carbon atom. In this case, only a molecule having a polymerizable group and not having an asymmetric carbon atom functions as a discotic liquid crystalline molecule, and a molecule having an asymmetric carbon atom and having no polymerizable group is a chiral agent. It can be considered that it functions as (described later).
[0071]
The non-polymerizable discotic liquid crystalline molecule is preferably a compound in which the polymerizable group (Q) of the polymerizable discotic liquid crystalline molecule is changed to a hydrogen atom or an alkyl group. That is, the non-polymerizable discotic liquid crystalline molecule is preferably a compound represented by the following formula.
D (-LR)_n
Where D is a discotic core; L is a divalent linking group; R is a hydrogen atom or an alkyl group; and n is an integer from 4 to 12.
The example of the discotic core (D) of the above formula is the same as the above-described example of the polymerizable discotic liquid crystal molecule except that LQ (or QL) is changed to LR (or RL). Examples of the divalent linking group (L) are the same as the examples of the polymerizable discotic liquid crystal molecules.
The alkyl group for R preferably has 1 to 40 carbon atoms, and more preferably 1 to 30 carbon atoms. A chain alkyl group is preferred to a cyclic alkyl group, and a linear alkyl group is preferred to a branched chain alkyl group. R is particularly preferably a hydrogen atom or a linear alkyl group having 1 to 30 carbon atoms.
[0072]
Instead of introducing an asymmetric carbon atom into the divalent linking group (L) of the discotic liquid crystal molecule, an optically active compound containing a chiral carbon atom (chiral agent) is added to the optically anisotropic layer. However, the discotic liquid crystal molecules can be twisted and aligned in a spiral shape. As a compound containing an asymmetric carbon atom, various natural or synthetic compounds can be used. In the compound containing an asymmetric carbon atom, the same or similar polymerizable group as the discotic liquid crystalline molecule may be introduced. When a polymerizable group is introduced, a compound containing an asymmetric carbon atom is optically anisotropic due to the same or similar polymerization reaction at the same time that the discotic liquid crystal molecule is fixed after being substantially vertically (homogeneous) aligned. It can be fixed in the sex layer.
[0073]
In order to align the discotic liquid crystalline molecules substantially vertically (homogeneously) and uniformly even on the air interface side, a fluorine-containing surfactant or cellulose ester can be added to the optically anisotropic layer.
The fluorine-containing surfactant is composed of a hydrophobic group containing a fluorine atom, a nonionic, anionic, cationic or amphoteric hydrophilic group and an optionally provided linking group. The fluorine-containing surfactant composed of one hydrophobic group and one hydrophilic group is represented by the following formula.
Rf-L^Five-Hy
In the formula, Rf is a monovalent hydrocarbon group substituted with a fluorine atom;^FiveIs a single bond or a divalent linking group, and Hy is a hydrophilic group.
The above Rf functions as a hydrophobic group. The hydrocarbon group is preferably an alkyl group or an aryl group. The alkyl group preferably has 3 to 30 carbon atoms, and the aryl group preferably has 6 to 30 carbon atoms.
Some or all of the hydrogen atoms contained in the hydrocarbon group are substituted with fluorine atoms. It is preferable to replace 50% or more of the hydrogen atoms contained in the hydrocarbon group with fluorine atoms, more preferably 60% or more, more preferably 70% or more, and more preferably 80% or more. Most preferably.
The remaining hydrogen atoms may be further substituted with other halogen atoms (eg, chlorine atom, bromine atom).
An example of Rf is shown below.
[0074]
Rf1: n-C₈F₁₇−
Rf2: n-C₆F₁₃−
Rf3: Cl- (CF₂-CFCl)_Three-CF₂−
Rf4: H- (CF₂)₈−
Rf5: H- (CF₂)_Ten−
Rf6: n-C₉F₁₉−
Rf7: Pentafluorophenyl
Rf8: n-C₇F₁₅−
Rf9: Cl- (CF₂-CFCl)₂-CF₂−
Rf10: H- (CF₂)_Four−
Rf11: H- (CF₂)₆−
Rf12: Cl- (CF₂)₆−
Rf13: C_ThreeF₇−
[0075]
In the above formula, the divalent linking group is an alkylene group, an arylene group, a divalent heterocyclic residue, -CO-, -NR- (R is an alkyl group having 1 to 5 carbon atoms or a hydrogen atom), -O-, -SO₂It is preferably a divalent linking group selected from the group consisting of-and combinations thereof.
L in the above formula^FiveAn example of this is shown below. The left side is bonded to the hydrophobic group (Rf), and the right side is bonded to the hydrophilic group (Hy). AL represents an alkylene group, AR represents an arylene group, and Hc represents a divalent heterocyclic residue. In addition, the alkylene group, the arylene group, and the divalent heterocyclic residue may have a substituent (eg, an alkyl group).
[0076]
L0: Single bond
L51: -SO₂-NR-
L52: -AL-O-
L53: -CO-NR-
L54: -AR-O-
L55: -SO₂-NR-AL-CO-O-
L56: -CO-O-
L57: -SO₂-NR-AL-O-
L58: -SO₂-NR-AL-
L59: -CO-NR-AL-
L60: -AL-O-AL-
L61: -Hc-AL-
L62: -SO₂-NR-AL-O-AL-
L63: -AR-
L64: -O-AR-SO₂-NR-AL-
L65: -O-AR-SO₂-NR-
L66: -O-AR-O-
[0077]
Hy in the above formula is any of a nonionic hydrophilic group, an anionic hydrophilic group, a cationic hydrophilic group, or an amphoteric hydrophilic group. Nonionic hydrophilic groups are particularly preferred.
Examples of Hy in the above formula are shown below.
[0078]
Hy1 :-( CH₂CH₂O)_n-H (n is an integer of 5 to 30)
Hy2:-(CH₂CH₂O)_n-R¹
(N is an integer from 5 to 30, R¹Is an alkyl group having 1 to 6 carbon atoms)
Hy3:-(CH₂CHOHCH₂)_n-H (n is an integer of 5 to 30)
Hy4: -COOM (M is a hydrogen atom, an alkali metal atom or a dissociated state)
Hy5: -SO_ThreeM (M is a hydrogen atom, an alkali metal atom or a dissociated state)
Hy6:-(CH₂CH₂O)_n-CH₂CH₂CH₂-SO_ThreeM
(N is an integer of 5 to 30, M is a hydrogen atom or an alkali metal atom)
Hy7: -OPO (OH)₂
Hy8: -N⁺(CH_Three)_Three・ X^-(X is a halogen atom)
Hy9: -COONH_Four
[0079]
Nonionic hydrophilic groups (Hy1, Hy2, Hy3) are preferred, and hydrophilic groups (Hy1) made of polyethylene oxide are most preferred.
A fluorine-containing surfactant having two or more hydrophobic groups or hydrophilic groups containing fluorine atoms may be used. Two or more fluorine-containing surfactants may be used in combination.
Regarding fluorine-containing surfactants, various documents (eg, Hiroshi Horiguchi “New Surfactant”, Sankyo Publishing (1975), MJ Schick, Nonionic Surfactants, Marcell Dekker Inc., New York, (1967), JP-A-7 No. 13293).
The fluorine-containing surfactant is preferably in the range of 0.01 to 30% by weight, more preferably 0.05 to 10% by weight, and more preferably 0.1 to 5% by weight of the amount of the discotic liquid crystalline molecule. % Is more preferable.
[0080]
As the cellulose ester, it is preferable to use a lower fatty acid ester of cellulose.
The “lower fatty acid” in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. The number of carbon atoms is preferably 2 to 5, and more preferably 2 to 4. A substituent (eg, hydroxy) may be bonded to the fatty acid. Two or more types of fatty acids may form an ester with cellulose. Examples of lower fatty acid esters of cellulose include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose hydroxypropionate, cellulose acetate propionate and cellulose acetate butyrate. Cellulose acetate butyrate is particularly preferred. The degree of butyrylation of cellulose acetate butyrate is preferably 30% or more, and more preferably 30 to 80%. The degree of acetylation of cellulose acetate butyrate is preferably 30% or less, and more preferably 1 to 30%.
Cellulose ester is 0.005 to 0.5 g / m²Is preferably used in an amount in the range of 0.01 to 0.45 g / m.²Is more preferably in the range of 0.02 to 0.4 / m.²Is more preferably in the range of 0.03 to 0.35 / m.²Most preferably, it is in the range. It is also preferable to use it in an amount of 0.1 to 5% by weight of the amount of discotic liquid crystalline molecules.
[0081]
The optically anisotropic layer is a coating containing discotic liquid crystalline molecules, and if necessary, a compound containing an asymmetric carbon atom, a fluorine-containing surfactant, a cellulose ester, or the following polymerization initiator or other additives. The liquid is formed by applying on the alignment film.
As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.
[0082]
The coating liquid can be applied by a known method (eg, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method, bar coating method).
The discotic liquid crystal molecules that are substantially vertically (homogeneously) aligned are fixed while maintaining the alignment state. The immobilization is preferably performed by a polymerization reaction of the polymerizable group (Q) introduced into the discotic liquid crystalline molecule. 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).
[0083]
The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight, more preferably 0.5 to 5% by weight, based on the solid content of the coating solution.
Light irradiation for polymerization of discotic liquid crystalline molecules is preferably performed using ultraviolet rays.
Irradiation energy is 20mJ / cm²~ 50J / cm²Preferably, 100 to 2000 mJ / cm²More preferably. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.
The thickness of the optically anisotropic layer is preferably 0.1 to 50 μm, more preferably 1 to 30 μm, and most preferably 5 to 20 μm. When two optical compensation sheets are used in the liquid crystal display device, the thickness may be half of the thickness of the optically anisotropic layer (a preferable range described above) required when using one optical compensation sheet.
The average tilt angle of the discotic liquid crystalline molecules in the optically anisotropic layer is 50 to 90 degrees. The inclination angle is preferably as uniform as possible. However, if the tilt angle changes continuously along the thickness direction of the optically anisotropic layer, there is no problem even if there is a slight variation.
[0084]
The twist angle (twist angle) of the discotic liquid crystal molecules is similar (preferably ± 10 degrees) depending on the twist angle (generally 180 to 360 degrees, preferably more than 180 degrees to 270 degrees) of the STN type liquid crystal cell. The angle is preferably adjusted so that the angle is within the range of When one optical compensation sheet is used in the liquid crystal display device, the twist angle of the discotic liquid crystalline molecules is preferably in the range of 180 to 360 degrees. When two optical compensation sheets are used in the liquid crystal display device, the twist angle of the discotic liquid crystal molecules is preferably in the range of 90 to 180 degrees.
When the optical compensation sheet is used in an STN type liquid crystal display device, the wavelength dependence (Δn (λ)) of the birefringence of the optically anisotropic layer depends on the wavelength dependence of the birefringence of the liquid crystal in the STN type liquid crystal cell. A close value is preferable.
[0085]
[Liquid Crystal Display]
As described above, the present invention is particularly effective in a liquid crystal display device using STN type liquid crystal cells.
The STN type liquid crystal display device includes an STN type liquid crystal cell, one or two optical compensation sheets disposed on one side or both sides of the liquid crystal cell, and a pair of polarizing plates disposed on both sides thereof.
The relationship between the orientation direction of the rod-like liquid crystalline molecules in the liquid crystal cell and the orientation direction of the discotic liquid crystalline molecules is as follows. The director of the discotic liquid crystal molecule (normal direction of the disk-shaped core plane) of the optical compensation sheet closest to the cell is substantially the same (less than ± 10 °) when viewed from the normal direction of the liquid crystal cell. It is preferable to arrange so that.
The transparent support of the optical compensation sheet can also function as a protective film on the liquid crystal cell side of the polarizing film. In that case, arrange so that the slow axis (direction in which the refractive index is maximum) of the transparent support and the transmission axis of the polarizing film are substantially perpendicular or substantially parallel (less than ± 10 °). Is preferred.
[0086]
【Example】
[Example 1]
A triacetylcellulose film (Fujitac, manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 100 μm and a size of 270 mm × 100 mm was used as a transparent support. A polyimide (PI1) having an aromatic ring or aromatic heterocycle in the side chain was dissolved in a mixed solvent of methanol and acetone (volume ratio = 50/50) to prepare a 5 wt% solution. This solution was applied to a thickness of 1 μm on a transparent support using a bar coater. The coating layer was dried with warm air at 130 ° C. for 2 minutes, and the surface was rubbed to form an alignment film.
On the alignment film, a coating solution having the following composition was applied by an extrusion method.
[0087]

[0088]
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[0089]
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[0090]
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[0091]
The coating layer was heated at 130 ° C. for 2 minutes to align the discotic liquid crystalline compound substantially vertically. At that temperature, ultraviolet rays were irradiated for 4 seconds to polymerize the discotic liquid crystalline compound, and the alignment state was fixed. In this manner, an optically anisotropic layer in which the discotic liquid crystalline compound was oriented vertically and twisted was formed to produce an optical compensation sheet.
Polarized light is incident on the optical compensation sheet from the transparent support side at an angle of 45 ° to the rubbing axis of the alignment film, and the polarization analysis of the emitted light is performed using an optical device (Multi Chanel Photo Analyzer, manufactured by Otsuka Electronics Co., Ltd.). And the twist angle was determined to be 230 to 250 °.
[0092]
Separately, except that the discotic liquid crystalline compound (2) is removed from the coating solution for the optically anisotropic layer, the optical compensation is made so that the discotic liquid crystalline compound is oriented substantially vertically but is not twisted. Created a sheet. With respect to this sheet, in-plane retardation (Re) was measured using an ellipsometer, and the average inclination angle was determined from the angle dependency, and found to be 70 to 85 °.
Separately, an antiparallel cell was prepared using a horizontal alignment film, and the above discotic liquid crystalline compounds (1) and (2) were sealed in the cell. With respect to the obtained liquid crystal cell, in-plane retardation (Re) was measured using an ellipsometer, and Δn was determined by dividing the value by the thickness of the cell, which was 0.07.
[0093]
[Example 2]
An optical compensation sheet was prepared and evaluated in the same manner as in Example 1 except that the same amount of polyimide (PI5) was used instead of polyimide (PI1). The average tilt angle of the discotic liquid crystalline compound was 75 °.
[0094]
[Example 3]
An optical compensation sheet was prepared and evaluated in the same manner as in Example 1 except that the same amount of polyimide (PI10) was used instead of polyimide (PI1). The average tilt angle of the discotic liquid crystalline compound was 70 °.
[0095]
[Example 4]
An optical compensation sheet was prepared and evaluated in the same manner as in Example 1 except that the same amount of polyimide (PI13) was used instead of polyimide (PI1). The average tilt angle of the discotic liquid crystalline compound was 75 °.
[0096]
[Comparative Example 1]
An inorganic vertical alignment film forming material (EXP-OA004, manufactured by Nissan Chemical Industries, Ltd.) was diluted with methanol to a solid content of 2% by weight. This was coated on a glass plate with a bar coater so as to have a thickness of 0.4 μm, and dried at 140 ° C. for 10 minutes to form an alignment film.
After rubbing the alignment film, two antiparacels were prepared. In one cell, rod-like liquid crystalline molecules (MBBA) were inserted. In the other cell, a solution obtained by evaporating methyl ethyl ketone from the optically anisotropic layer coating solution used in Example 1 (discotic liquid crystalline molecules) was inserted.
For each cell, the alignment state of liquid crystal molecules was examined. In the cell in which rod-like liquid crystal molecules were inserted, the rod-like liquid crystal molecules were nematically aligned in the direction perpendicular to the glass plate. On the other hand, in the cell in which the discotic liquid crystal molecules were inserted, the average tilt angle was 30 ° and the vertical alignment (50 to 90 °) was not achieved.
The used inorganic vertical alignment film forming material is commercially available as a vertical alignment film for rod-like liquid crystal molecules, and is most commonly used. Experimental results using other commercially available vertical alignment films for rod-like liquid crystalline molecules revealed that commercially available vertical alignment films for rod-like liquid crystalline molecules have insufficient functions for vertically aligning discotic liquid crystalline molecules. did.
[0097]
[Example 5]
Using the optical compensation sheet prepared in Example 1, an STN type liquid crystal display device having the structure shown in FIG. On the surface where the liquid crystal cell and the optical compensation sheet are in contact, the alignment direction of the rod-like liquid crystalline molecules of the liquid crystal cell and the alignment direction of the discotic liquid crystalline molecules of the optical compensation sheet were matched. The angle between the absorption axis of the exit side polarizing plate and the orientation direction of the rod-like liquid crystalline molecules on the exit side of the liquid crystal cell was adjusted to 45 °. The absorption axis of the incident side polarizing plate and the absorption axis of the outgoing side polarizing plate were arranged so as to be orthogonal to each other.
When a voltage was applied to the obtained STN type liquid crystal display device, a normally black mode was obtained. When the visual characteristics were measured, an angle range with a contrast ratio of 5 or more was obtained at 120 ° or more on the left and right and 150 ° or more on the top and bottom.
[Brief description of the drawings]
FIG. 1 shows the alignment state of rod-like liquid crystal molecules in a liquid crystal cell and the alignment state of discotic liquid crystal molecules in an optically anisotropic layer in a pixel portion where no voltage is applied (off) in an STN type liquid crystal display device. It is sectional drawing shown typically.
FIG. 2 is a schematic diagram showing refractive index ellipsoids of rod-like liquid crystalline molecules of a liquid crystal cell and discotic liquid crystalline molecules of an optical compensation sheet in a relationship for optical compensation thereof.
FIG. 3 is a schematic diagram showing a layer structure of an STN type liquid crystal display device.
FIG. 4 is a plan view showing a preferable optical direction for each element of the STN type liquid crystal display device.
FIG. 5 is a plan view showing another preferable optical direction for each element of the STN type liquid crystal display device.
[Explanation of symbols]
1 Liquid crystal cell
2, 2a, 2b Optical compensation sheet
3, 3a, 3b Polarizing plate
11 Upper substrate of liquid crystal cell
12, 14 Alignment film for liquid crystal cell
13 Refractive index ellipsoid of rod-like liquid crystalline molecules
13a-13e Rod-like liquid crystalline molecules
13t Thickness of rod-like liquid crystalline molecular layer
13x, 13y In-plane refractive index parallel to alignment film of rod-like liquid crystalline molecules
13z Refractive index in the thickness direction of rod-like liquid crystalline molecules
15 Lower substrate of liquid crystal cell
21 Index ellipsoid of discotic liquid crystalline molecules
21a-21e discotic liquid crystalline molecules
21t Discotic liquid crystalline molecular layer thickness
21x, 21y In-plane refractive index parallel to the alignment film of discotic liquid crystalline molecules
21z Refractive index in the thickness direction of discotic liquid crystalline molecules
22 Alignment film
23 Transparent support
BL backlight
DDa, DDb, DDc, DDd Normal direction of disc surface of discotic liquid crystalline molecules
RDa, RDb Rubbing direction of alignment film of liquid crystal cell
TAa, TAb Polarization axis of polarizing plate
X Reference direction

Claims (7)

An optical compensation sheet having, in this order, an alignment film and an optically anisotropic layer formed of discotic liquid crystalline molecules on a transparent support, the alignment film having an aromatic ring or aromatic heterocycle in the side chain Between the main chain of the polymer and the aromatic ring or the aromatic heterocycle on the most main chain side is -O-, -O-CO-, -O-CO- NH-, -O-CO-NH-alkylene group-, -O-CO-NH-alkylene group -O-, -O-CO-NH-alkylene group -CO-O- and -O-CO-NH-alkylene Linked via a linking group selected from the group consisting of the groups -CO-NH- (the left side is bonded to the main chain and the right side is bonded to the most aromatic ring or aromatic heterocycle on the main chain side) , discotic liquid crystal molecules distribution at an average inclined angle in the range of 50 to 90 degrees The optical compensation sheet characterized in that it.   2. The optical compensation sheet according to claim 1, wherein the main chain of the polymer has a polyimide structure.   The optical compensation sheet according to claim 1, wherein the polymer has a biphenyl structure in at least one of a main chain and a side chain.   The optical compensation sheet according to claim 1, wherein the discotic liquid crystal molecules are twisted and the twist angle is in the range of 90 to 360 degrees. -O-, -O-CO-, -O-CO-NH-, -O-CO-NH-alkylene between the main chain of the polymer and the aromatic ring or aromatic heterocycle on the most main chain side A linking group selected from the group consisting of a group -O-, -O-CO-NH-alkylene group -CO-O- and -O-CO-NH-alkylene group -CO-NH- (the left side is bonded to the main chain. The optical compensation sheet according to claim 1, wherein the right side is connected via an aromatic ring or an aromatic heterocyclic ring on the most main chain side. STN type liquid crystal display comprising STN type liquid crystal cell, two polarizing plates arranged on both sides thereof, and one or two optical compensation sheets arranged between STN type liquid crystal cell and one or both polarizing plates The optical compensation sheet has an optically anisotropic layer formed from a transparent support, an alignment film, and discotic liquid crystalline molecules in this order from the polarizing plate side, and the alignment film has an aromatic ring in the side chain. Or a polymer containing 2 to 4 aromatic heterocycles, wherein the chain between the main chain and the most aromatic ring or aromatic heterocycle is -O-, -O-CO -, -O-CO-NH-, -O-CO-NH-alkylene group-, -O-CO-NH-alkylene group -O-, -O-CO-NH-alkylene group -CO-O- and- Group consisting of O—CO—NH-alkylene group —CO—NH— Are connected via a linking group (the left side is bonded to the main chain and the right side is bonded to the most aromatic ring or aromatic heterocycle on the main chain side). An STN type liquid crystal display device characterized by being oriented at an average tilt angle in the range of 90 degrees, further twisted, and having a twist angle in the range of 90 to 360 degrees. A polymer containing 2 to 4 aromatic rings or aromatic heterocycles in the side chain, and -O- between the main chain of the polymer and the aromatic ring or aromatic heterocycle on the most main chain side , -O-CO-, -O-CO-NH-, -O-CO-NH-alkylene group-, -O-CO-NH-alkylene group -O-, -O-CO-NH-alkylene group -CO A linking group selected from the group consisting of —O— and —O—CO—NH-alkylene group —CO—NH— (the left side is bonded to the main chain, and the right side is the most aromatic ring or aromatic heterocycle on the main chain side). A method of aligning discotic liquid crystalline molecules with an average tilt angle in the range of 50 to 90 degrees using an alignment film connected via a ring).

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