JP2005017574A - Optical compensating sheet, polarizing plate, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the display performance of a liquid crystal display device without causing a problem like light leak. <P>SOLUTION: A cellulose acylate film which has an intra-face retardation value in the range of 0 to 20 nm, a thickness in the range of 10 to 85 nm, the average of the minimum value and the maximum value of acoustic velocity which are measured within the face of the film in the range of 2.2 to 2.5 km/sec and the ratio of the maximum value to the minimum value of the acoustic velocity which are measured in the face of the film in the range of 1.01 to 1.12 is used as an optical compensating sheet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

式中、ｌは、２乃至４の整数を表し；ｍは、２乃至４の整数を表し；ｎは、１乃至１００の整数を表す。
さらに詳細に述べると、その構成ポリエステルは、グリコール成分が、エチレングリコール、１，３−プロパンジオール、または１，４−ブタンジオールであり、二塩基性酸成分は、コハク酸、グルタル酸、またはアジピン酸からなる両未満ヒドロオキシル基を有するポリエステルであり、その重合度ｎは１〜１００の範囲にある。重合度ｎは、１〜１００の範囲にあればよいが、その最適な重合度は、用いるグリコールおよび二塩基性酸の種類により若干異なり、ポリエステルの分子量として１０００乃至４５００の範囲となることが特に好ましい。
ジクロロメタン可溶のポリエステルウレタン樹脂は、（１）式のポリエステルとジイソシアナートとの反応により得られ、一般式としては（２）式で表されるような繰返し単位の化合物である。
【００３６】

式中、ｌは、２乃至４の整数を表し；ｍは、２乃至４の整数を表し；ｎは、１乃至１００の整数を表し；Ｒは、２価の原子団残基を表わす。
２価の原子団残基の例としては、例えば下式のようなものが挙げられる。
【００３７】
【化１】

【００３８】
ポリウレタン化合物に用いられるジイソシアナート成分の例には、エチレンジイソシアナート、トリメチレンジイソシアナート、テトラメチレンジイソシアナート、ヘキサメチレンジイソシアナートで代表されるポリメチレンジイソシアナート（一般式：ＯＣＮ−（ＣＨ_２ ）ｐ −ＮＣＯ（ｐは、２〜８の整数を表す））、芳香族ジイソシアナート（例えば、ｐ−フェニレンジイソシアナート、トリレンジイソシアナート、ｐ，ｐ’−ジフェニルメタンジイソシアナート、１，５−ナフチレンジイソシアナート）およびｍ−キシリレンジイソシアナートが含まれる。トリレンジイソシアナート、ｍ−キシリレンジイソシアナートおよびテトラメチレンジイソシアナートは、入手も容易であり、比較的安定で取扱いも容易であり、そして、ポリウレタン化した場合にセルロースアシレートとの相溶性が優れているので好ましい。
【００３９】
ポリエステルウレタン樹脂の分子量は、２０００乃至５００００の範囲にあることが好ましい。分子量は、成分ポリエステル類またはこれらの連結グループであるジイソシアナート成分の種類又は分子量により、適宜調節できる。ポリエステルウレタン樹脂の分子量は、セルロースアシレートフイルムの機械的物性の向上とセルロースアシレートに対する相溶性の点で、５０００乃至１５０００の範囲にあることがさらに好ましい。
ジクロロメタン可溶性ポリエステルウレタンの合成は、（１）式で表わされるポリエステルジオール類とジイソシアナートとを混合し、攪拌下加熱することにより容易に得ることができる。
（１）式で表わされるポリエステル類は、相当する二塩基性酸もしくはそのアルキルエステル類と、グリコール類とのポリエステル化反応もしくはエステル交換反応による熱溶融縮合法、あるいは、これらの酸の酸クロリドとグリコール類との界面縮合法のいずれかの方法により、末端基がヒドロキシル基となるよう適宜調整すれば容易に合成できる。
ジクロロメタン可溶性ポリエステルウレタン樹脂は、酢化度５８％以上のセルロースアシレートと極めて相溶性がよい。樹脂の構造により若干の相異は認められるが、ポリエステルウレタンの分子量が１００００以下の場合、酢酸繊維素１００質量部に対してポリエステルウレタン２００質量部でも相溶する。
【００４０】
従って、ポリエステルウレタン樹脂をセルロースアシレートに混合し、その皮膜の機械的物性を改善しようとする場合、ポリエステルウレタン樹脂の含有量は、ウレタン樹脂の種類、分子量、所望の機械的物性により適当に定めればよい。
セルロースアシレートの特性を保持したまま機械的物性を改善しようとする場合には、セルロースアシレートに対して、ポリエステルウレタン樹脂を１０乃至５０質量％含有させることが好ましい。
また、このポリエステルウレタン樹脂は、少くとも１８０℃までは安定で熱分解しない。このジクロロメタン可溶性のポリエステルウレタン類は、特に５８％以上の酢化度のセルロースアシレートに対して極めて相溶性がよい。従って、両者を混合して製膜すると、極めて透明度の高いフイルムが得られる。しかも、これらのポリエステルウレタン類は、その平均分子量が高いため、従来の低分子の可塑剤とは異なり、高温においても揮発性は殆んどない。従って、これらの混合物より製膜して得られた皮膜は、その後の加工において、従来の可塑剤においてみられた可塑剤の揮発や、移行による不都合が少ない。
【００４１】
ポリエステルウレタンをセルロースアシレートフイルムに添加することにより、高温および低温における耐折強度および引裂き強度が大きくなり、そして、フイルムが裂けるような不都合がなくなる。従来、皮膜の耐折強度や引裂き強度を向上するのに、低分子可塑剤が用いられていた。この方法では、常温、高湿状態においてはある程度の効果はあるが、低温、高湿状態においては皮膜の柔軟性がなくなり、必ずしも満足すべき結果は得られなかった。さらに、低分子可塑剤により機械的性質の改善を試みると、可塑剤の添加量と共に引張り強度の様な機械的性質が著しく低下するのが一般的であった。
ジクロロメタン可溶性ポリエステルウレタン樹脂をセルロースアシレートに添加した場合は、樹脂の添加量と共に若干の引張り強度の低下は認められるが、低分子可塑剤添加の場合と比較して、明らかに強度の低下が少く、無添加の場合とほぼ同等の耐折強度の大きい強靱なフイルムが得られる。さらに、このポリエステルウレタンを混合することにより、低温、高湿における可塑剤の移行を防止できる。そのため、フイルム相互が接着せず、かつ非常に柔軟性があり、しわもきしむことのない透明で光沢のあるフイルムが得られる。
【００４２】
セルロースアシレートフイルムには機械的物性を改良するために、上記のポリエステルウレタンを添加することが好ましいが、ポリエステルウレタンに代え、またはポリエステルウレタンと併用して、以下の可塑剤を用いることができる。可塑剤としては、リン酸エステルまたはカルボン酸エステルが用いられる。リン酸エステルの例には、トリフェニルフォスフェート（ＴＰＰ）およびトリクレジルホスフェート（ＴＣＰ）が含まれる。カルボン酸エステルとしては、フタル酸エステルおよびクエン酸エステルが代表的である。フタル酸エステルの例には、ジメチルフタレート（ＤＭＰ）、ジエチルフタレート（ＤＥＰ）、ジブチルフタレート（ＤＢＰ）、ジオクチルフタレート（ＤＯＰ）、ジフェニルフタレート（ＤＰＰ）およびジエチルヘキシルフタレート（ＤＥＨＰ）が含まれる。クエン酸エステルの例には、Ｏ−アセチルクエン酸トリエチル（ＯＡＣＴＥ）およびＯ−アセチルクエン酸トリブチル（ＯＡＣＴＢ）が含まれる。その他のカルボン酸エステルの例には、オレイン酸ブチル、リシノール酸メチルアセチル、セバシン酸ジブチル、種々のトリメリット酸エステルが含まれる。フタル酸エステル系可塑剤（ＤＭＰ、ＤＥＰ、ＤＢＰ、ＤＯＰ、ＤＰＰ、ＤＥＨＰ）が好ましく用いられる。ＤＥＰおよびＤＰＰが特に好ましい。
可塑剤の添加量は、セルロースエステルの量の０．１乃至２５質量％であることが好ましく、１乃至２０質量％であることがさらに好ましく、３乃至１５質量％であることが最も好ましい。
【００４３】
セルロースアシレートフイルムには、劣化防止剤（例、酸化防止剤、過酸化物分解剤、ラジカル禁止剤、金属不活性化剤、酸捕獲剤、アミン）を添加してもよい。劣化防止剤については、特開平３−１９９２０１号、同５−１９０７０７３号、同５−１９４７８９号、同５−２７１４７１号、同６−１０７８５４号の各公報に記載がある。劣化防止剤の添加量は、調製する溶液（ドープ）の０．０１乃至１質量％であることが好ましく、０．０１乃至０．２質量％であることがさらに好ましい。添加量が０．０１質量％未満であると、劣化防止剤の効果がほとんど認められない。添加量が１質量％を越えると、フイルム表面への劣化防止剤のブリードアウト（滲み出し）が認められる場合がある。特に好ましい劣化防止剤の例としては、ブチル化ヒドロキシトルエン（ＢＨＴ）、トリベンジルアミン（ＴＢＡ）を挙げることができる。
【００４４】
［二軸延伸］
セルロースアセテートフイルムは、仮想歪みを低減させるために、適宜、延伸処理をすることが好ましい。延伸することにより、延伸方向の仮想歪みが低減できるので、面内すべての方向で歪みを低減するために二軸延伸することがさらに好ましい。但し、製造上のハンドリングの観点から、上述の音速範囲となるように延伸することが、更に好ましい。
二軸延伸には、同時二軸延伸法と逐次二軸延伸法があるが、連続製造の観点から逐次二軸延伸方法が好ましく、ドープを流延した後、バンドもしくはドラムよりフイルムを剥ぎ取り、幅方向（長手方法）に延伸した後、長手方向（幅方向）に延伸される。
幅方向に延伸する方法は、例えば、特開昭６２−１１５０３５号、特開平４−１５２１２５号、同４−２８４２１１号、同４−２９８３１０号、同１１−４８２７１号の各公報に記載されている。フイルムの延伸は、常温または加熱条件下で実施する。加熱温度は、フイルムのガラス転移温度以下であることが好ましい。フイルムは、乾燥中の処理で延伸することができ、特に溶媒が残存する場合は有効である。長手方向の延伸の場合、例えば、フイルムの搬送ローラーの速度を調節して、フイルムの剥ぎ取り速度よりもフイルムの巻き取り速度の方を速くするとフイルムは延伸される。幅方向の延伸の場合、フイルムの巾をテンターで保持しながら搬送して、テンターの巾を徐々に広げることによってもフイルムを延伸できる。フイルムの乾燥後に、延伸機を用いて延伸すること（好ましくはロング延伸機を用いる一軸延伸）もできる。フイルムの延伸倍率（元の長さに対する延伸による増加分の比率）は、０乃至５０％の範囲にあることが好ましく、１０乃至４０％の範囲にあることがさらに好ましく、１５乃至３５％の範囲にあることが最も好ましい。
【００４５】
流延から乾燥までの工程は、空気雰囲気下でもよいし窒素ガスなどの不活性ガス雰囲気下でもよい。セルロースアシレートフイルムの製造に用いる巻き取り機は一般的に使用されているものでよい。例えば、定テンション法、定トルク法、テーパーテンション法、内部応力一定のプログラムテンションコントロール法のような巻き取り方法で巻き取ることができる。
【００４６】
［吸湿膨張係数］
吸湿膨張係数は、一定温度下において相対湿度を変化させた時の試料の長さの変化量を示す。
額縁状の透過率上昇を防止するために、セルロースアシレートフイルムの吸湿膨張係数は、３０×１０^−５／％ＲＨ以下とすることが好ましく、１５×１０^−５／％ＲＨ以下とすることが更に好ましく、１０×１０^−５／％ＲＨ以下とすることが最も好ましい。また、吸湿膨張係数は小さい方が好ましいが、通常は、１．０×１０^−５／％ＲＨ以上の値である。
吸湿膨張係数の測定方法について以下に示す。作製したポリマーフイルム（位相差板）から幅５ｍｍ、長さ２０ｍｍの試料を切り出し、片方の端を固定して２５℃、２０％ＲＨ（Ｒ０）の雰囲気下にぶら下げた。他方の端に０．５ｇの重りをぶら下げて、１０分間放置し長さ（Ｌ０）を測定した。次に、温度は２５℃のまま、湿度を８０％ＲＨ（Ｒ１）にして、長さ（Ｌ１）を測定した。吸湿膨張係数は下式により算出した。測定は同一試料につき１０サンプル行い、平均値を採用した。
吸湿膨張係数［／％ＲＨ］＝｛（Ｌ１−Ｌ０）／Ｌ０｝／（Ｒ１−Ｒ０）
【００４７】
上記吸湿による寸度変化は、ポリマーフイルム中の自由体積を小さくすればよいことを見出した。自由体積を大きく左右するのは、製膜時の残留溶剤量であり、少ない方が寸度変化は少ない。
残留溶剤を減らすための一般的手法は、高温かつ長時間で乾燥することであるが、あまり長時間であると、当然のことながら生産性が落ちる。従ってセルロースアシレートフイルムに対する残留溶剤の量は、０．０１乃至１質量％の範囲にあることが好ましく、０．０２乃至０．０７質量％の範囲にあることがさらに好ましく、０．０３乃至０．０５質量％の範囲にあることが最も好ましい。
上記残留溶剤量を制御することにより、光学補償能を有する偏光板を安価に高い生産性で製造することができる。
【００４８】
残留溶剤量は、固形分質量に対する揮発分の量を意味し、下記式で定義される。
残留溶媒量（質量％）＝（（Ｗ−Ｗ０）／Ｗ０）×１００
Ｗ： 試料軟膜質量
Ｗ０：試料軟膜を１１０℃、２時間乾燥した後の試料質量
残留溶剤量は、一定量の試料をクロロフォルムに溶解し、ガスクロマトグラフ（ＧＣ１８Ａ、島津製作所（株）製）を用いて測定した。
【００４９】
溶液流延法では、ポリマー材料を有機溶媒に溶解した溶液（ドープ）を用いてフイルムを製造する。溶液流延法での乾燥は、後述するように、ドラム（またはバンド）面での乾燥と、フイルム搬送時の乾燥に大きく分かれる。ドラム（またはバンド）面での乾燥時には、使用している溶剤の沸点を越えない温度（沸点を越えると泡となる）でゆっくりと乾燥させることが好ましい。
本発明のセルロースアシレートフイルムを実現するためには、ドラム（またはバンド）から剥離直後に加温することが重要である。加温の温度は、１１０℃乃至１６０℃が好ましく、１２０℃乃至１５０℃がさらに好ましい。
また、フイルム搬送時の乾燥は、ポリマー材料のガラス転移点±３０℃、更に好ましくは±２０℃で行うことが好ましい。
【００５０】
また、上記吸湿による寸度変化を小さくする別な方法として、疎水基を有する化合物を添加することが好ましい。疎水基を有する素材としては、分子中にアルキル基やフェニル基のような疎水基を有する素材であれば特に制限はないが、前記のセルロースアシレートフイルムに添加する可塑剤や劣化防止剤の中で該当する素材が特に好ましく用いられる。その例としては、トリフェニルフォスフェート（ＴＰＰ）、トリベンジルアミン（ＴＢＡ）を挙げることができる。
これらの疎水基を有する化合物の添加量は、調整する溶液（ドープ）に対して０．０１乃至１０質量％の範囲にあることが好ましく、０．１乃至５質量％の範囲にあることがさらに好ましく、１乃至３質量％の範囲にあることが最も好ましい。
【００５１】
［セルロースアシレートフイルムの表面処理］
セルロースアシレートフイルムは、表面処理を施すことが好ましい。具体的方法としては、コロナ放電処理、グロー放電処理、火炎処理、酸処理、アルカリ処理または紫外線照射処理が挙げられる。また、下塗り層（例えば、特開平７−３３３４３３号公報に記載）を設けることも好ましい。
フイルムの平面性を保持する観点から、これら処理においてセルロースアシレートフイルムの温度をＴｇ（ガラス転移温度）以下、具体的には１５０℃以下とすることが好ましい。
偏光板の透明保護膜として使用する場合、偏光膜との接着性の観点から、酸処理またはアルカリ処理、すなわちセルロースアシレートに対するケン化処理を実施することが特に好ましい。
表面エネルギーは５５ｍＮ／ｍ以上であることが好ましく、６０ｍＮ／ｍ以上７５ｍＮ／ｍ以下であることが更に好ましい。
【００５２】
以下、特に好ましいアルカリ鹸化処理について、具体的に説明する。
セルロースアシレートフイルムのアルカリ鹸化処理は、フイルム表面をアルカリ溶液に浸漬した後、酸性溶液で中和し、水洗して乾燥するサイクルで行われることが好ましい。
アルカリ溶液としては、水酸化カリウム溶液、水酸化ナトリウム溶液が挙げられ、水酸化イオンの規定濃度は０．１乃至３．０Ｎの範囲にあることが好ましく、０．５乃至２．０Ｎの範囲にあることがさらに好ましい。アルカリ溶液温度は、室温乃至９０℃の範囲にあることが好ましく、４０乃至７０℃の範囲にあることがさらに好ましい。
【００５３】
固体の表面エネルギーは、「ぬれの基礎と応用」（リアライズ社 １９８９．１２．１０発行）に記載のように接触角法、湿潤熱法、および吸着法により求めることができる。本発明のセルロースアシレートフイルムの場合、接触角法を用いることが好ましい。
具体的には、表面エネルギーが既知である２種の溶液をセルロースアシレートフイルムに滴下し、液滴の表面とフイルム表面との交点において、液滴に引いた接線とフイルム表面のなす角で、液滴を含む方の角を接触角と定義し、計算によりフイルムの表面エネルギーを算出できる。
【００５４】
光学補償シートは、作製したセルロースアシレートフイルムの上に、液晶性化合物から形成された光学異方性層を設けることができる。セルロースアシレートフイルムと、その上に設ける光学異方性層との間に、配向膜を設けることが好ましい。配向膜は本発明で用いる液晶性化合物を一定の方向に配向させる働きをする。従って、配向膜は本発明の光学補償シートを製造する上では必須である。しかし、液晶性化合物を配向後にその配向状態を固定してしまえば、配向膜はその役割を果たしているために、光学補償シートの構成要素としては必ずしも必須のものではない。すなわち、配向状態が固定された配向膜上の光学異方性層のみをセルロースアシレートフイルム上に転写して光学補償シートを作製することも可能である。
【００５５】
［配向膜］
配向膜は、液晶性化合物の配向方向を規定する機能を有する。配向膜は、有機化合物（好ましくはポリマー）のラビング処理、無機化合物の斜方蒸着、マイクログルーブを有する層の形成、あるいはラングミュア・ブロジェット法（ＬＢ膜）による有機化合物（例、ω−トリコサン酸、ジオクタデシルメチルアンモニウムクロライド、ステアリル酸メチル）の累積のような手段で、設けることができる。さらに、電場の付与、磁場の付与あるいは光照射により、配向機能が生じる配向膜も知られている。配向膜は、ポリマーのラビング処理により形成することが好ましい。
【００５６】
配向膜は、ポリマーのラビング処理により形成することが好ましい。ポリビニルアルコールが、好ましいポリマーである。疎水性基が結合している変性ポリビニルアルコールが特に好ましい。
配向膜は、一種類のポリマーから形成することもできるが、架橋された二種類のポリマーからなる層をラビング処理することにより形成することがさらに好ましい。少なくとも一種類のポリマーとして、それ自体架橋可能なポリマーか、架橋剤により架橋されるポリマーのいずれかを用いることが好ましい。
配向膜は、官能基を有するポリマーあるいはポリマーに官能基を導入したものを、光、熱、ＰＨ変化等により、ポリマー間で反応させて形成するか；あるいは、反応活性の高い化合物である架橋剤を用いてポリマー間に架橋剤に由来する結合基を導入して、ポリマー間を架橋することにより形成することができる。
【００５７】
このような架橋は、上記ポリマーまたはポリマーと架橋剤の混合物を含む配向膜塗布液を、セルロースアシレートフイルム上に塗布したのち、加熱等を行なうことにより実施される。最終商品（光学補償シート）で耐久性が確保できれば良いので、配向膜をセルロースアシレートフイルム上に塗設した後から、光学補償シートを得るまでのいずれの段階で架橋させる処理を行なっても良い。
配向膜上に形成される液晶性化合物からなる層（光学異方性層）の配向性を考えると、液晶性化合物を配向させたのちに、充分架橋を行なうことも好ましい。
配向膜の架橋は、セルロースアシレートフイルム上に配向膜塗布液を塗布し、加熱乾燥することで行われることが一般的である。この塗布液の加熱温度を低く設定して、後述の光学異方性層を形成する際の加熱処理の段階で配向膜の充分な架橋を行うことが好ましい。
【００５８】
配向膜に用いるポリマーとしては、それ自体架橋可能なポリマーあるいは架橋剤により架橋されるポリマーのいずれも使用することができる。勿論両方可能なポリマーもある。ポリマーの例としては、ポリメチルメタクリレート、アクリル酸／メタクリル酸共重合体、スチレン／マレインイミド共重合体、ポリビニルアルコール及び変性ポリビニルアルコール、ポリ（Ｎ−メチロールアクリルアミド）、スチレン／ビニルトルエン共重合体、クロロスルホン化ポリエチレン、ニトロセルロース、ポリ塩化ビニル、塩素化ポリオレフィン、ポリエステル、ポリイミド、酢酸ビニル／塩化ビニル共重合体、エチレン／酢酸ビニル共重合体、カルボキシメチルセルロース、ポリエチレン、ポリプロピレンおよびポリカーボネートを挙げることができる。ポリマーの代わりにシランカップリング剤を用いることができる。
好ましいポリマーは、水溶性ポリマー（例、ポリ（Ｎ−メチロールアクリルアミド）、カルボキシメチルセルロース、ゼラチン、ポリビニルアルコール、変性ポリビニルアルコール）である。ゼラチン、ポリビニルアルコールおよび変性ポリビニルアルコールが好ましく、ポリビニルアルコールおよび変性ポリビニルアルコールを用いることがさらに好ましい。
また、重合度の異なるポリビニルアルコールまたは変性ポリビニルアルコールを二種類併用することが最も好ましい。
【００５９】
ポリビニルアルコールは、鹸化度が７０乃至１００％の範囲にあることが好ましい。鹸化度は８０乃至１００％の範囲にあることがより好ましく、８５乃至９５％の範囲にあることがさらに好ましい。また、ポリビニルアルコールの重合度は、１００乃至３０００の範囲にあることが好ましい。
変性ポリビニルアルコールの例としては、共重合変性、連鎖移動による変性、またはブロック重合による変性をしたポリビニルアルコールなどを挙げることができる。共重合変性する場合の変性基の例としては、ＣＯＯＮａ、Ｓｉ（ＯＸ）_３ 、Ｎ（ＣＨ_３ ）_３ ・Ｃｌ、Ｃ_９ Ｈ_１９ＣＯＯ、ＳＯ_３ Ｎａ、Ｃ_１２Ｈ_２５が挙げられる。連鎖移動による変性をする場合の変性基の例としては、ＣＯＯＮａ、ＳＨ、Ｃ_１２Ｈ_２５が挙げられる。また、ブロック重合による変性をする場合の変性基の例としては、ＣＯＯＨ、ＣＯＮＨ_２ 、ＣＯＯＲ、Ｃ_６ Ｈ_５ が挙げられる。
鹸化度が８０乃至１００％の範囲にある未変性もしくは変性ポリビニルアルコールが好ましい。鹸化度が８５乃至９５％の範囲にある未変性ポリビニルアルコールおよび変性ポリビニルアルコールがさらに好ましい。
【００６０】
変性ポリビニルアルコールとしては、特に、下記一般式で表わされる化合物によるポリビニルアルコールの変性物を用いることが好ましい。この変性ポリビニルアルコールを、以下、特定の変性ポリビニルアルコールと記載する。
【００６１】
【化２】

【００６２】
式中、Ｒ^１ は、アルキル基、アクリロイルアルキル基、メタクリロイルアルキル基、またはエポキシアルキル基を表わし；Ｗは、ハロゲン原子、アルキル基、またはアルコキシ基を表わし；Ｘは、活性エステル、酸無水物、または酸ハロゲン化物を形成するために必要な原子群を表わし；ｐは、０または１を表わし；そして、ｎは、０乃至４の整数を表わす。
上記の特定の変性ポリビニルアルコールは、さらに下記一般式で表わされる化合物によるポリビニルアルコールの変性物であることが好ましい。
【００６３】
【化３】

【００６４】
式中、Ｘ^１ は、活性エステル、酸無水物、または酸ハロゲン化物を形成するために必要な原子群を表わし、そしてｍは２乃至２４の整数を表わす。
【００６５】
これらの一般式により表される化合物と反応させるために用いるポリビニルアルコールとしては、前述の、未変性のポリビニルアルコール、および、共重合変性したもの、即ち連鎖移動により変性したもの、ブロック重合による変性をしたものなどのポリビニルアルコールの変性物を挙げることができる。特定の変性ポリビニルアルコールの好ましい例は、特開平９−１５２５０９号公報に記載されている。
これらポリマーの合成方法、可視吸収スペクトル測定、および変性基導入率の決定方法等、特開平８−３３８９１３号公報に記載がある。
【００６６】
架橋剤の例としては、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、およびジアルデヒド澱粉を挙げることができる。アルデヒド類の例としては、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挙げられる。Ｎ−メチロール化合物の例としては、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挙げられる。ジオキサン誘導体の例としては、２，３−ジヒドロキシジオキサンが挙げられる。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としては、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）が挙げられる。活性ビニル化合物の例としては、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ー（ビニルスルホニル）プロピオンアミド］が挙げられる。そして、活性ハロゲン化合物の例としては、２，４−ジクロロ−６−ヒドロキシ−Ｓ−トリアジンが挙げられる。これらは組み合わせて用いることができる。
これらは上記水溶性ポリマー、特にポリビニルアルコール及び変性ポリビニルアルコール（上記特定の変性物も含む）と併用する場合に好ましい。生産性を考慮した場合、反応活性の高いアルデヒド類、とりわけグルタルアルデヒドの使用が好ましい。
【００６７】
耐湿性は、架橋剤を多く添加した方が良化傾向にある。しかし、架橋剤をポリマーに対して５０質量％以上添加した場合には、配向膜としての配向能が低下する。従って、ポリマーに対する架橋剤の添加量は、０．１乃至２０質量％の範囲にあることが好ましく、０．５乃至１５質量％の範囲にあることがさらに好ましい。配向膜は、架橋反応が終了した後でも、反応しなかった架橋剤をある程度含んでいるが、その架橋剤の量は、配向膜中に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。配向膜中に１．０質量％を超える量で未反応の架橋剤が含まれていると、充分な耐久性が得られない。即ち、液晶表示装置に使用した場合、長期使用、あるいは高温高湿の雰囲気下に長期間放置した場合に、レチキュレーションが発生することがある。
【００６８】
配向膜は、上記ポリマーを含む溶液、あるいは上記ポリマーと架橋剤を含む溶液を、セルロースアシレートフイルム上に塗布した後、加熱乾燥し（架橋させ）、ラビング処理することにより形成することができる。架橋反応は、塗布液をセルロースアシレートフイルム上に塗布した後、任意の時期に行なっても良い。
そして、ポリビニルアルコール等の水溶性ポリマーを配向膜形成材料として用いる場合、その塗布液を作製するための溶媒は、消泡作用のあるメタノール等の有機溶媒とするか、あるいは有機溶媒と水の混合溶媒とすることが好ましい。有機溶媒としてメタノールを用いる場合、その比率は質量比で水：メタノールが、０：１００〜９９：１が一般的であり、０：１００〜９１：９であることがさらに好ましい。これにより、泡の発生が抑えられ、配向膜、更には光学異方性層の表面の欠陥が著しく減少する。
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及びＥ型塗布法を挙げることができる。特にＥ型塗布法が好ましい。
【００６９】
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。加熱乾燥は、加熱温度が２０乃至１１０℃の範囲で行なうことができる。充分な架橋を形成させるためには、加熱温度は６０乃至１００℃の範囲にあることが好ましく、８０乃至１００℃の範囲にあることがさらに好ましい。乾燥時間は１分〜３６時間で行なうことができる。好ましくは５乃至３０分間である。ｐＨも、使用する架橋剤に最適な値に設定することが好ましく、グルタルアルデヒドを使用した場合は、ｐＨ４．５乃至５．５の範囲にあることが好ましく、特にｐＨ５であることが好ましい。
【００７０】
ラビング処理は、ＬＣＤの液晶配向処理工程として広く採用されている処理方法を利用することができる。即ち、配向膜の表面を、紙やガーゼ、フェルト、ゴムあるいはナイロン、ポリエステル繊維などを用いて一定方向に擦ることにより配向を得る方法を用いることができる。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などを用いて数回程度ラビングを行うことにより実施される。
【００７１】
［光学異方性層］
液晶性化合物から形成される光学異方性層を、セルロースアシレートフイルム上に設けられた配向膜の上に形成することができる。
光学異方性層に用いる液晶性化合物には、棒状液晶性化合物および円盤状液晶性化合物が含まれる。棒状液晶性化合物および円盤状液晶性化合物は、高分子液晶でも低分子液晶でもよく、さらに、低分子液晶が架橋され液晶性を示さなくなったものも含まれる。
光学異方性層は、液晶性化合物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。
【００７２】
塗布液の調整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、テトラクロロエタン）、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。
塗布液の塗布は、公知の方法（例、ワイヤーバーコーティング法、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）により実施できる。
光学異方性層の厚さは、０．１乃至２０μｍであることが好ましく、０．５乃至１５μｍであることがさらに好ましく、１乃至１０μｍであることが最も好ましい。
【００７３】
棒状液晶性化合物としては、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、棒状液晶性化合物には、金属錯体も含まれる。また、棒状液晶性化合物を繰り返し単位中に含む液晶ポリマーも、棒状液晶性化合物として用いることができる。言い換えると、棒状液晶性化合物は、（液晶）ポリマーと結合していてもよい。
棒状液晶性化合物については、季刊化学総説第２２巻液晶の化学（１９９４）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。
棒状液晶性化合物の複屈折率は、０．００１乃至０．７の範囲にあることが好ましい。
棒状液晶性化合物は、その配向状態を固定するために、重合性基を有することが好ましい。重合性基（Ｑ）の例を、以下に示す。
【００７４】
【化４】

【００７５】
【化５】

【００７６】
【化６】

【００７７】
【化７】

【００７８】
【化８】

【００７９】
【化９】

【００８０】
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。
棒状液晶性化合物は、短軸方向に対してほぼ対称となる分子構造を有することが好ましい。そのためには、棒状分子構造の両端に重合性基を有することが好ましい。
以下に、棒状液晶性化合物の例を示す。
【００８１】
【化１０】

【００８２】
【化１１】

【００８３】
【化１２】

【００８４】
【化１３】

【００８５】
【化１４】

【００８６】
【化１５】

【００８７】
【化１６】

【００８８】
【化１７】

【００８９】
【化１８】

【００９０】
【化１９】

【００９１】
【化２０】

【００９２】
【化２１】

【００９３】
【化２２】

【００９４】
【化２３】

【００９５】
【化２４】

【００９６】
【化２５】

【００９７】
【化２６】

【００９８】
【化２７】

【００９９】
【化２８】

【０１００】
【化２９】

【０１０１】
【化３０】

【０１０２】
【化３１】

【０１０３】
【化３２】

【０１０４】
【化３３】

【０１０５】
【化３４】

【０１０６】
【化３５】

【０１０７】
【化３６】

【０１０８】
【化３７】

【０１０９】
【化３８】

【０１１０】
【化３９】

【０１１１】
【化４０】

【０１１２】
【化４１】

【０１１３】
【化４２】

【０１１４】
【化４３】

【０１１５】
【化４４】

【０１１６】
【化４５】

【０１１７】
【化４６】

【０１１８】
【化４７】

【０１１９】
【化４８】

【０１２０】
【化４９】

【０１２１】
【化５０】

【０１２２】
【化５１】

【０１２３】
【化５２】

【０１２４】
【化５３】

【０１２５】
【化５４】

【０１２６】
【化５５】

【０１２７】
【化５６】

【０１２８】
光学異方性層は、棒状液晶性化合物あるいは後述の重合性開始剤や任意の添加剤（例、可塑剤、モノマー、界面活性剤、セルロースエステル、１，３，５−トリアジン化合物、カイラル剤）を含む液晶組成物（塗布液）を、配向膜の上に塗布することで形成できる。
【０１２９】
円盤状（ディスコティック）液晶性化合物の例としては、Ｃ．Ｄｅｓｔｒａｄｅらの研究報告、Ｍｏｌ．Ｃｒｙｓｔ．７１巻、１１１頁（１９８１年）に記載されているベンゼン誘導体、Ｃ．Ｄｅｓｔｒａｄｅらの研究報告、Ｍｏｌ．Ｃｒｙｓｔ．１２２巻、１４１頁（１９８５年）、Ｐｈｙｓｉｃｓ ｌｅｔｔ，Ａ，７８巻、８２頁（１９９０）に記載されているトルキセン誘導体、Ｂ．Ｋｏｈｎｅらの研究報告、Ａｎｇｅｗ．Ｃｈｅｍ．９６巻、７０頁（１９８４年）に記載されたシクロヘキサン誘導体及びＪ．Ｍ．Ｌｅｈｎらの研究報告、Ｊ．Ｃｈｅｍ．Ｃｏｍｍｕｎ．，１７９４頁（１９８５年）、Ｊ．Ｚｈａｎｇらの研究報告、Ｊ．Ａｍ．Ｃｈｅｍ．Ｓｏｃ．１１６巻、２６５５頁（１９９４年）に記載されているアザクラウン系やフェニルアセチレン系マクロサイクルを挙げることができる。さらに、円盤状液晶性化合物としては、一般的にこれらを分子中心の母核とし、直鎖のアルキル基やアルコキシ基、置換ベンゾイルオキシ基等がその直鎖として放射線状に置換された構造のものも含まれ、液晶性を示す。また、本発明において、円盤状液晶性化合物から形成する光学異方性層は、最終的にできた物が前記化合物である必要はなく、例えば、低分子の円盤状液晶性化合物が熱や光で反応する基を有しており、結果的に熱、光等で反応により重合または架橋し、高分子量化し液晶性を失ったものも含まれる。円盤状液晶性化合物の好ましい例は、特開平８−５０２０６号公報に記載されている。また、円盤状液晶性化合物の重合については、特開平８−２７２８４公報に記載がある。
【０１３０】
円盤状液晶性化合物を重合により固定するためには、円盤状液晶性化合物の円盤状コアに、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、重合性基を有する円盤状液晶性化合物は、下記式（ＩＩＩ）で表わされる化合物であることが好ましい。
【０１３１】
（ＩＩＩ） 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。
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。
【０１３２】
【化５７】

【０１３３】
【化５８】

【０１３４】
【化５９】

【０１３５】
【化６０】

【０１３６】
【化６１】

【０１３７】
【化６２】

【０１３８】
【化６３】

【０１３９】
【化６４】

【０１４０】
【化６５】

【０１４１】
式（ＩＩＩ）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。
【０１４２】
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−
【０１４３】
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−
【０１４４】
式（ＩＩＩ）の重合性基（Ｑ）は、棒状液晶性化合物で説明した重合性基（Ｑ）と同様である。
式（ＩＩＩ）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。
【０１４５】
円盤状液晶性化合物を用いる場合、光学異方性層は負の複屈折を有する層であって、そして円盤状構造単位の面が、セルロースアシレートフイルム表面に対して傾き、且つ円盤状構造単位の面とセルロースアシレートフイルム表面とのなす角度が、光学異方性層の深さ方向に変化していることが好ましい。
【０１４６】
円盤状構造単位の面の角度（傾斜角）は、一般に、光学異方性層の深さ方向でかつ光学異方性層の底面からの距離の増加と共に増加または減少している。傾斜角は、距離の増加と共に増加することが好ましい。さらに、傾斜角の変化としては、連続的増加、連続的減少、間欠的増加、間欠的減少、連続的増加と連続的減少を含む変化、及び増加及び減少を含む間欠的変化などを挙げることができる。間欠的変化は、厚さ方向の途中で傾斜角が変化しない領域を含んでいる。傾斜角は、傾斜角が変化しない領域を含んでいても、全体として増加または減少していることが好ましい。さらに、傾斜角は全体として増加していることが好ましく、特に連続的に変化することが好ましい。
【０１４７】
支持体側の円盤状単位の傾斜角は、一般に円盤状液晶性化合物あるいは配向膜の材料を選択することにより、またはラビング処理方法を選択することにより、調整することができる。また、表面側（空気側）の円盤状単位の傾斜角は、一般に円盤状液晶性化合物あるいは円盤状液晶性化合物とともに使用する他の化合物を選択することにより調整することができる。円盤状液晶性化合物とともに使用する化合物の例としては、可塑剤、界面活性剤、重合性モノマー及びポリマーなどを挙げることができる。更に、傾斜角の変化の程度も、上記と同様の選択により調整できる。
【０１４８】
円盤状液晶性化合物と共に使用する可塑剤、界面活性剤及び重合性モノマーとしては、円盤状液晶性化合物と相溶性を有し、円盤状液晶性化合物の傾斜角の変化を与えられるか、あるいは配向を阻害しない限り、どのような化合物も使用することができる。これらの中で、重合性モノマー（例、ビニル基、ビニルオキシ基、アクリロイル基及びメタクリロイル基を有する化合物）が好ましい。上記化合物の添加量は、円盤状液晶性化合物に対して一般に１乃至５０質量％の範囲にあり、５乃至３０質量％の範囲にあることが好ましい。
【０１４９】
円盤状液晶性化合物とともに使用するポリマーとしては、円盤状液晶性化合物と相溶性を有し、円盤状液晶性化合物に傾斜角の変化を与えられる限り、どのようなポリマーでも使用することができる。ポリマーの例としては、セルロースエステルを挙げることができる。セルロースエステルの好ましい例としては、セルロースアセテート、セルロースアセテートプロピオネート、ヒドロキシプロピルセルロース及びセルロースアセテートブチレートを挙げることができる。円盤状液晶性化合物の配向を阻害しないように、上記ポリマーの添加量は、円盤状液晶性化合物に対して一般に０．１乃至１０質量％の範囲にあり、０．１乃至８質量％の範囲にあることがより好ましく、０．１乃至５質量％の範囲にあることがさらに好ましい。
【０１５０】
光学異方性層は、一般に円盤状液晶性化合物および他の化合物を溶剤に溶解した溶液を配向膜上に塗布し、乾燥し、次いでディスコティックネマチック相形成温度まで加熱し、その後配向状態（ディスコティックネマチック相）を維持して冷却することにより得られる。あるいは、上記光学異方性層は、円盤状液晶性化合物及び他の化合物（更に、例えば重合性モノマー、光重合開始剤）を溶剤に溶解した溶液を配向膜上に塗布し、乾燥し、次いでディスコティックネマチック相形成温度まで加熱したのち重合させ（ＵＶ光の照射等により）、さらに冷却することにより得られる。円盤状液晶性化合物のディスコティックネマティック液晶相−固相転移温度は、７０乃至３００℃が好ましく、７０乃至１７０℃がさらに好ましい。
【０１５１】
［液晶性化合物の配向状態の固定］
配向させた液晶性化合物を、配向状態を維持して固定することができる。固定化は、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（米国特許第２３６７６６１号、同第２３６７６７０号の各明細書記載）、アシロインエーテル（米国特許第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（米国特許第２７２２５１２号明細書記載）、多核キノン化合物（米国特許第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（米国特許第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、米国特許第４２３９８５０号明細書記載）およびオキサジアゾール化合物（米国特許第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％の範囲にあることが好ましく、０．５乃至５質量％の範囲にあることがさらに好ましい。
液晶性化合物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／ｃｍ^２ 乃至５０Ｊ／ｃｍ^２ の範囲にあることが好ましく、２０乃至５０００ｍＪ／ｃｍ^２ の範囲にあることがさらに好ましく、１００乃至８００ｍＪ／ｃｍ^２ の範囲にあることが最も好ましい。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。
【０１５２】
［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。一方の保護膜として、上記の光学補償シートを用いることができる。他方の保護膜は、通常のセルロースアセテートフイルムを用いてもよい。
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。
【０１５３】
また、偏光板の生産性には保護フイルムの透湿性が重要であることがわかった。偏光膜と保護フイルムは水系接着剤で貼り合わせられており、この接着剤溶剤は保護フイルム中を拡散することで、乾燥される。保護フイルムの透湿性が高ければ、高いほど乾燥は早くなり、生産性は向上するが、高くなりすぎると、液晶表示装置の使用環境（高湿下）により、水分が偏光膜中に入ることで偏光能が低下する。
光学補償シートの透湿性は、ポリマーフイルム（および重合性液晶化合物）の厚み、自由体積、もしくは、親疎水性などにより決定される。
光学補償シートを偏光板の保護フイルムとして用いる場合、光学補償シートの透湿性は１００乃至１０００（ｇ／ｍ^２ ）／２４ｈｒｓの範囲にあることが好ましく、３００乃至７００（ｇ／ｍ^２ ）／２４ｈｒｓの範囲にあることがさらに好ましい。
【０１５４】
光学補償シートの厚みは、セルロースアシレートフイルムを製膜する場合の、リップ流量とラインスピード、あるいは、延伸、圧縮により調整することができる。使用する主素材により透湿性が異なるので、厚み調整により好ましい範囲にすることが可能である。
光学補償シートの自由体積は、製膜の場合、乾燥温度と時間により調整することができる。この場合もまた、使用する主素材により透湿性が異なるので、自由体積調整により好ましい範囲にすることが可能である。
光学補償フイルムの親疎水性は、添加剤により調整することができる。自由体積中に親水的添加剤を添加することで透湿性は高くなり、逆に疎水性添加剤を添加することで透湿性を低くすることができる。
光学補償シートの透湿性を調整することにより、光学補償能を有する偏光板を安価に高い生産性で製造することが可能となる。
【０１５５】
［液晶表示装置］
光学補償シート、または光学補償シートと偏光膜とを貼り合わせて得られた偏光板は、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。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。液晶セルは、二枚の電極基板の間に液晶を担持している。
本発明の光学補償シートは、液晶セルと一方の偏光板との間に一枚配置するか、あるいは液晶セルと双方の偏光板との間に二枚配置する。
本発明の偏光板は、液晶セルの両側に配置された二枚の偏光板のうちの少なくとも一方として用いればよい。この際には、光学補償シートが液晶セル側となるように本発明の偏光板を配置する。
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。
【０１５６】
【実施例】
［実施例１］
（セルロースアシレートフイルムの作製）
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、セルロースアシレート溶液を調製した。
【０１５７】
────────────────────────────────────
セルロースアシレート溶液組成
────────────────────────────────────
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） ２９５質量部
メタノール（第２溶媒） ６８質量部
１−ブタノール（第３溶媒） ２質量部
───────────────────────────────────
【０１５８】
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。
【０１５９】
【化６６】

【０１６０】
セルロースアシレート溶液４７４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、充分に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、３．５質量部であった。
得られたドープを、ドラム流延機を用いて流延した。ドラム上での膜面温度が４０℃となってから、７０℃の温風で１分乾燥し、揮発分が５５％の状態でドラムからフイルムを剥ぎ取り、その直後にフイルムを１４０℃の乾燥風で１分環乾燥し、さらに１３０℃の乾燥風で１５分間乾燥し、残留溶剤量が０．３質量％のセルロースアシレートフイルム（厚さ：８０μｍ）を製造した。
作製したセルロースアシレートフイルム（ＣＡＦ−０１）について、光学特性を測定した。結果は第１表に示す。
なお、光学特性は、エリプソメーター（Ｍ−１５０、日本分光（株）製）を用いて、波長５５０ｎｍにおけるＲｅレターデーション値およびＲｔｈレターデーション値を測定した。
作製したセルロースアシレートフイルムを２．０Ｎの水酸化カリウム溶液（２５℃）に２分間浸漬した後、硫酸で中和し、純水で水洗、乾燥した。このセルロースアシレートフイルム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。
【０１６１】
（配向膜の形成）
作製したセルロースアシレートフイルム上に、下記の組成の塗布液を＃１６のワイヤーバーコーターで２８ｍｌ／ｍ^２ 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、セルロースアシレートフイルムの長手方向と平行な方向に、形成した膜にラビング処理を実施した。
【０１６２】
────────────────────────────────────
配向膜塗布液組成
────────────────────────────────────
下記の変性ポリビニルアルコール １０質量部
水 ３７１質量部
メタノール １１９質量部
グルタルアルデヒド（架橋剤） ０．５質量部
────────────────────────────────────
【０１６３】
【化６７】

【０１６４】
（光学異方性層の形成）
配向膜上に、下記の円盤状液晶性化合物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）４．０６ｇ、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、＃３．６のワイヤーバーで塗布した。これを１３０℃の恒温ゾーンで２分間加熱し、円盤状液晶性化合物を配向させた。次に、６０℃の雰囲気下で１２０Ｗ／ｃｍ高圧水銀灯を用いて、１分間ＵＶ照射し円盤状液晶性化合物を重合させた。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、光学補償シート（ＫＨ−０１）を作製した。
【０１６５】
【化６８】

【０１６６】
波長５４６ｎｍで測定した光学異方性層のＲｅレターデーション値は４３ｎｍであった。また、円盤面と透明支持体（セルロースアシレートフイルム）面との間の角度（傾斜角）は平均で４２゜であった。
【０１６７】
［実施例２］
（セルロースアシレートフイルムの作製）
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、セルロースアシレート溶液を調製した。
【０１６８】
────────────────────────────────────
セルロースアシレート溶液組成
────────────────────────────────────
酢化度６０．７％のセルロースアセテート １００質量部
ポリエーテルウレタン １６質量部
（Ｂ−３２６、住友バイエルウレタン（株）、デスモコール１７６）
メチレンクロライド（第１溶媒） ２９０質量部
メタノール（第２溶媒） ７３質量部
１−ブタノール（第３溶媒） ２質量部
────────────────────────────────────
【０１６９】
別のミキシングタンクに、実施例１で用いた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。
セルロースアシレート溶液４８４質量部にレターデーション上昇剤溶液１５質量部を混合し、充分に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、２．０質量部であった。
【０１７０】
得られたドープを、ドラム流延機を用いて流延した。ドラム上での膜面温度が４０℃となってから、６５℃の温風で１分乾燥し、残留溶剤が６０％のフイルムをドラムから剥ぎ取った。次いでテンターにより、フイルムをその状態で幅方向に２０％延伸しながら、１３０℃の乾燥風で５分乾燥し、残留溶剤量を５質量％とした。さらにその状態でフイルムを長手方向に１８％延伸し、さらに１４０℃で１０分乾燥し、残留溶剤が０．３質量％のセルロースアシレートフイルム（厚さ：４０μｍ）を製造した。
作製したセルロースアシレートフイルム（ＣＡＦ−０２）について、光学特性を測定した。結果は第１表に示す。
なお、光学特性は、エリプソメーター（Ｍ−１５０、日本分光（株）製）を用いて、波長５５０ｎｍにおけるＲｅレターデーション値およびＲｔｈレターデーション値を測定した。
実施例１と同様に、セルロースアシレートフイルムに表面処理を行い、配向膜および光学異方性層を形成して、光学補償シート（ＫＨ−０２）を作製した。
【０１７１】
［比較例１］
（セルロースアシレートフイルムの作製）
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、セルロースアシレート溶液を調製した。
【０１７２】
────────────────────────────────────
セルロースアシレート溶液組成
────────────────────────────────────
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
────────────────────────────────────
【０１７３】
このセルロースアシレート溶液をそのままドープとして、バンド流延機を用いて流延した。バンド上での膜面温度が４０℃となってから、４０℃の温風で１分乾燥し、揮発分３０％の状態でバンドからフイルムを剥ぎ取った。次いでフイルムを１００℃の乾燥風で３０分乾燥し、残留溶剤量が０．９質量％のセルロースアシレートフイルム（厚さ：８０μｍ）を製造した。
作製したセルロースアシレートフイルム（ＣＡＦ−Ｈ１）について、光学特性を測定した。結果は第１表に示す。
【０１７４】
【表１】

註：音速は、野村商事（株）製のＳＳＴ−２５００型を用いて測定した。
【０１７５】
［実施例４］
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、ポリビニルアルコール系接着剤を用いて、実施例１で作製した光学補償シート（ＫＨ−０１）をセルロースアシレートフイルム（ＣＡＦ―０１）が偏光膜側となるように偏光膜の片側に貼り付けた。偏光膜の透過軸と光学補償シート（ＫＨ−０１）の遅相軸とは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）にケン化処理を行い、ポリビニルアルコール系接着剤を用いて、偏光膜の反対側に貼り付けた。このようにして偏光板を作製した。
【０１７６】
［実施例５］
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、ポリビニルアルコール系接着剤を用いて、実施例２で作製した光学補償シート（ＫＨ−０２）をセルロースアシレートフイルム（ＣＡＦ―０２）が偏光膜側となるように偏光膜の片側に貼り付けた。偏光膜の透過軸と光学補償シート（ＫＨ−０２）の遅相軸とは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）にケン化処理を行い、ポリビニルアルコール系接着剤を用いて、偏光膜の反対側に貼り付けた。このようにして偏光板を作製した。
【０１７７】
［比較例２］
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、ポリビニルアルコール系接着剤を用いて、比較例１で作製したセルロースアシレートフイルムを偏光膜の片側に貼り付けた。偏光膜の透過軸とセルロースアシレートフイルム（ＣＡＦ−Ｈ１）の遅相軸とは垂直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）にケン化処理を行い、ポリビニルアルコール系接着剤を用いて、偏光膜の反対側に貼り付けた。このようにして偏光板を作製した。
【０１７８】
［実施例７］
ＴＮ型液晶セルを使用した液晶表示装置（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、代わりに実施例４で作製した偏光板を、光学補償シート（ＫＨ−０１）が液晶セル側となるように粘着剤を介して、観察者側およびバックライト側に一枚ずつ貼り付けた。観察者側の偏光板の透過軸とバックライト側の偏光板の透過軸が直交するように配置した。
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。結果を第２表に示す。
【０１７９】
［実施例８］
ＴＮ型液晶セルを使用した液晶表示装置（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、代わりに実施例５で作製した偏光板を、光学補償シート（ＫＨ−０２）が液晶セル側となるように粘着剤を介して、観察者側およびバックライト側に一枚ずつ貼り付けた。観察者側の偏光板の透過軸とバックライト側の偏光板の透過軸が直交するように配置した。
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。結果を第２表に示す。
【０１８０】
［比較例３］
ＴＮ型液晶セルを使用した液晶表示装置（６Ｅ−Ａ３、シャープ（株）製）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。結果を第２表に示す。
【０１８１】
【表２】

（註）黒側の階調反転：Ｌ１とＬ２との間の反転
【０１８２】
［実施例１０］
ＴＮ型液晶セルを使用した２０インチの液晶表示装置（ＬＣ−２０Ｖ１、シャープ（株）製）に設けられている一対の偏光板を剥がし、代わりに実施例４で作製した偏光板を、光学補償シート（ＫＨ−０１）が液晶セル側となるように粘着剤を介して、観察者側およびバックライト側に一枚ずつ貼り付けた。観察者側の偏光板の透過軸と、バックライト側の偏光板の透過軸とが直交するように配置した。
温度２５℃、相対湿度６０％の環境条件において、バックライトを５時間連続点灯し、全面黒表示状態を暗室にて目視で観察して光漏れを評価した。その結果、液晶表示装置の表示画面において光漏れは観測されなかった。
【０１８３】
［実施例１１］
実施例５で作製した偏光板を用いる以外は、実施例１０と同様にして偏光板を液晶表示装置に実装した。
実施例１０と同様にして光漏れを評価した。その結果、液晶表示装置の表示画面において光漏れは観測されなかった。
【０１８４】
［比較例４］
比較例２で作製した偏光板を用いる以外は、実施例１０と同様にして偏光板を液晶表示装置に実装した。
実施例１０と同様にして、光漏れを評価した。その結果、液晶表示装置の表示画面において額縁状の光漏れが観測された。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical compensation sheet made of a cellulose acylate film. The present invention also relates to a polarizing plate and a liquid crystal display device using an optical compensation sheet. The present invention further relates to a method for producing a cellulose acylate film.
[0002]
[Prior art]
The liquid crystal display device is composed of a polarizing plate and a liquid crystal cell.
In the current mainstream TN mode TFT liquid crystal display device, an optical compensation sheet is further inserted between the polarizing plate and the liquid crystal cell to improve the display quality of the liquid crystal display device. However, when an optical compensation sheet is used, there is a problem that the liquid crystal display device becomes thick.
The polarizing plate is composed of a polarizing film and two transparent protective films disposed on both sides thereof. By using a polarizing plate (elliptical polarizing plate) in which one transparent protective film also functions as an optical compensation sheet (retardation film), the display quality is improved without increasing the thickness of the liquid crystal display device (for example, the front contrast is improved). (For example, see Patent Document 1).
[0003]
The optical compensation sheet is likely to be distorted and phase difference due to heat and has a problem in durability. When a frame-like light leakage (increased transmittance) occurs in the liquid crystal display device due to the generated phase difference, the display quality of the liquid crystal display device is degraded.
In order to solve the problem of phase difference due to distortion, it is proposed to use an optical compensation sheet in which an optically anisotropic layer made of a discotic compound is coated on a transparent support as a protective film for a polarizing plate. (For example, see Patent Documents 2 and 3).
However, in recent years, liquid crystal display devices have become larger in size, and problems that should have been solved by conventional techniques are becoming apparent again. For example, when a polarizing plate using a conventional optical compensation sheet as a protective film is mounted on a liquid crystal display device composed of a large panel of 17 inches or more, light leakage due to thermal distortion is recognized again.
It has been reported that this light leakage can be solved by reducing the thickness of the transparent support of the optical compensation sheet (see, for example, Patent Document 4).
[0004]
[Patent Document 1]
JP-A-1-68940
[Patent Document 2]
Japanese Patent Laid-Open No. 7-191217
[Patent Document 3]
European Patent Application No. 0911656A2
[Patent Document 4]
JP 2002-169023 A
[0005]
[Problems to be solved by the invention]
Recently, liquid crystal display devices have become larger.
In a liquid crystal display device composed of a large panel of 20 inches or more, problems that have not been studied at all in the prior art have been recognized. In addition, light leakage due to thermal distortion is recognized again.
In order to solve the problem caused by thermal distortion, the optical compensation sheet is required not only to have a function of optically compensating the liquid crystal cell but also to have excellent durability against changes in the use environment.
An object of the present invention is to optically compensate a liquid crystal cell using an optical compensation sheet.
Another object of the present invention is to arrange an optical compensation sheet on one side of a polarizing film and use it in a liquid crystal display device, thereby improving the display quality of the liquid crystal display device without causing problems such as light leakage. That is.
Yet another object of the present invention is to add an optical compensation function to a polarizing plate without increasing the number of components of the polarizing plate.
[0006]
[Means for Solving the Problems]
The present invention provides the following optical compensation sheet, polarizing plate, liquid crystal display device and method for producing a cellulose acylate film.
(1) An optical compensation sheet comprising a cellulose acylate film, wherein the cellulose acylate film has (i) an in-plane retardation value in the range of 0 to 20 nm, (iii) a thickness in the range of 10 to 85 μm, (iv ) Average of the minimum and maximum sound speeds measured in the film plane in the range of 2.2 to 2.5 km / sec, and (v) Measured in the film plane in the range of 1.01 to 1.12. An optical compensation sheet having a ratio of the maximum value to the minimum value of the sound speed.
[0007]
The in-plane retardation value (Re) is defined by the following formula (I).
(I) Re = (nx−ny) × d
Where nx is the refractive index in the slow axis direction in the cellulose acylate film; ny is the refractive index in the fast axis direction in the cellulose acylate film; and d is the cellulose acylate film. This is the thickness of the rate film (unit: nm). Unless otherwise defined, the wavelength of light used for measurement is 550 nm.
Further, in this specification, “slow axis” means a direction in which the refractive index becomes maximum, and “fast axis” means a direction in which the refractive index becomes minimum.
The cellulose acylate film used in the present invention has an in-plane retardation value (Re) satisfying the following formula (i).
(I) 0 nm ≦ Re <20 nm
[0008]
The cellulose acylate film used in the present invention satisfies the following formula (iii) in thickness (d).
(Iii) 10 μm (= 10000 nm) <d <85 μm (= 85000 nm)
In the cellulose acylate film used in the present invention, the average ((Vmin + Vmax) / 2) of the minimum value (Vmin) and the maximum value (Vmax) of the sound velocity measured in the film plane satisfies the following formula (iv).
(Iv) 2.2 km / sec <(Vmin + Vmax) / 2 <2.5 km / sec
In the formula, Vmin is the sound velocity in the direction where the sound velocity is minimum in the cellulose acylate film surface; Vmax is the sound velocity in the direction where the sound velocity is maximum in the cellulose acylate film surface. Unless otherwise defined, measurement is performed using a plurality of frequencies in the range of 10 KHz to 100 MHz.
In the cellulose acylate film used in the present invention, the ratio (Vmax / Vmin) of the maximum value (Vmax) to the minimum value (Vmin) of the sound velocity measured in the film plane satisfies the following formula (v).
(V) 1.01 <Vmax / Vmin <1.12
In the formula, Vmin is the sound velocity in the direction where the sound velocity is minimum in the cellulose acylate film surface; Vmax is the sound velocity in the direction where the sound velocity is maximum in the cellulose acylate film surface.
[0009]
(2) An optical compensation sheet comprising an optically anisotropic layer formed from a cellulose acylate film and a liquid crystalline compound, wherein the cellulose acylate film has (i) an in-plane retardation value in the range of 0 to 20 nm, (Iii) a thickness in the range of 10 to 85 μm, (iv) an average of minimum and maximum sound speeds measured in the film plane in the range of 2.2 to 2.5 km / sec, and (v) An optical compensation sheet having a ratio of a maximum value to a minimum value of sound speed measured in a film plane in a range of 01 to 1.12.
[0010]
(3) The optical compensation sheet according to (1) or (2), wherein the cellulose acylate film has a retardation value in the thickness direction in the range of (ii) 70 to 400 nm.
The retardation value (Rth) in the thickness direction is defined by the following formula (II).
(II) Rth = {(nx + ny) / 2−nz} × d
In the formula, nx is the refractive index in the slow axis direction in the plane of the cellulose acylate film; ny is the refractive index in the fast axis direction in the plane of the cellulose acylate film; nz is the cellulose acylate film. And d is the thickness (unit: nm) of the cellulose acylate film. Unless otherwise defined, the wavelength of light used for measurement is 550 nm.
The cellulose acylate film used in the present invention preferably has a retardation value (Rth) in the thickness direction that satisfies the following formula (ii).
(Ii) 70 nm <Rth <400 nm
[0011]
(4) The optical compensation sheet according to (1) or (2), wherein the cellulose acylate film is a cellulose acetate film.
(5) The optical compensation sheet according to (4), wherein the cellulose acetate film comprises cellulose acetate having an acetylation degree in the range of 59.0 to 61.5%.
(6) The optical compensation sheet according to (1) or (2), wherein the cellulose acylate film contains an aromatic compound having at least two aromatic rings.
(7) The optical compensation sheet according to (6), comprising 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 acylate.
(8) The optical compensation sheet according to (6), wherein the aromatic compound has at least one 1,3,5-triazine ring.
[0012]
(9) The optical compensation sheet according to (2), wherein the liquid crystalline compound is a discotic liquid crystalline compound.
(10) A polarizing plate comprising a polarizing film and two transparent protective films disposed on both sides thereof, wherein one of the transparent protective films is the optical compensation sheet according to (1) or (2) A characteristic polarizing plate.
(11) A liquid crystal display device comprising a liquid crystal cell and two polarizing plates disposed on both sides thereof, wherein the polarizing plate comprises a polarizing film and two transparent protective films disposed on both sides thereof, At least one of the transparent protective films between polarizing films is the optical compensation sheet as described in (1) or (2), The liquid crystal display device characterized by the above-mentioned.
(13) The liquid crystal display device according to (11), wherein the liquid crystal cell is a TN mode liquid crystal cell.
(14) A cellulose acylate film is cast on a metal substrate, peeled off from the metal substrate, and then dried. In the method for producing a cellulose acylate film, the residual volatile content of the cellulose acylate film after peeling is 45 to 70%. The method for producing a cellulose acylate film is characterized by drying with hot air of 100 to 160 ° C. for 10 to 1000 seconds.
[0013]
【The invention's effect】
In order to optically compensate the liquid crystal cell, an optical compensation sheet made of a cellulose acylate film or an optical compensation sheet made of a liquid crystalline compound and an optically anisotropic layer and a cellulose acylate film is used in a liquid crystal display device. be able to.
When the optical compensation sheet is used in a liquid crystal display device, the optical compensation sheet is generally fixed to the liquid crystal cell with an adhesive. Accordingly, when the polymer film used for the optical compensation sheet expands or contracts, the generated distortion is suppressed as a whole of the optical compensation sheet, and the optical characteristics of the polymer film change.
[0014]
According to the study of the present inventor, it has been found that the change in the optical characteristics is caused by two causes. One cause is that the polymer film expands or contracts due to changes in wet heat conditions in the usage environment of the liquid crystal display device, and the optical characteristics of the optical compensation sheet change. Another cause is that a temperature distribution is generated in the surface of the optical compensation sheet due to a heat source (for example, a backlight) in the liquid crystal display device, and a change in optical characteristics is caused by the thermal distortion.
Cellulose acylate is generally difficult to fully acylate and has some hydroxyl groups. And it became clear that it was easy to be influenced by environmental conditions by a hydroxyl group.
[0015]
In order to eliminate light leakage, it is only necessary to suppress fluctuations in the optical characteristics of the optical compensation sheet due to environmental conditions.
The variation in optical characteristics is related to the photoelastic coefficient, thickness, virtual strain due to the environment, and elastic modulus of the optical compensation sheet. Therefore, light leakage is remarkably reduced by lowering the photoelastic coefficient of the optical compensation sheet, reducing the thickness, reducing distortion due to the environment, and reducing the elastic modulus.
As a result of further research by the present inventor, in order to achieve both the function as an optical compensation sheet (Re, preferably Rth control in addition) and industrial ease of manufacture, and to prevent the above light leakage It was found that the speed of sound in the cellulose acylate film should be adjusted so as to satisfy the above (iv) and (v).
The speed of sound in the film plane can be easily measured with a commercially available apparatus (for example, Sonic Test Tester SST-2500, Nomura Shoji).
[0016]
As described above, according to the present invention, a liquid crystal cell can be optically compensated without problems using an optical compensation sheet having a conventional thickness or less. Furthermore, by using the optical compensation sheet according to the present invention for a liquid crystal display device, an increase in the frame-like transmittance can be suppressed.
In the present invention, the thickness of the cellulose acylate film used for the optical compensation sheet is adjusted in the range of 10 to 85 μm in order to suppress the increase in the frame-like transmittance. Then, the speed of sound in the cellulose acylate film surface is adjusted so as to satisfy the above-mentioned (iv) and (v).
By adjusting the thickness and speed of sound of the cellulose acylate film within the above-mentioned range, the above-mentioned problems can be achieved without deteriorating the handling property of the optical compensation sheet in the production process of producing the optical compensation sheet or attaching it to the polarizing plate. Can be solved.
Furthermore, since the thickness of the optical compensation sheet is reduced, the thickness of the liquid crystal display device can be reduced, and the demand for thinning the liquid crystal display device can be met. The protective film of the polarizing plate is generally made of a cellulose acylate film. When the above optical compensation sheet is used as one protective film of the polarizing plate, an optical compensation function can be added to the polarizing plate without increasing the number of components of the polarizing plate.
The optical compensation sheet and the polarizing plate using the optical compensation sheet as a protective film can be advantageously used for a TN (Twisted Nematic) type liquid crystal display device.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
[Retardation of cellulose acylate film]
In the present invention, the Re retardation value of the cellulose acylate film is adjusted to a range of 0 to 20 nm. The Rth retardation value is preferably adjusted in the range of 70 to 400 nm.
When two optically anisotropic cellulose acylate films are used in the liquid crystal display device, the Rth retardation value of the film is preferably in the range of 70 to 250 nm.
When a single optically anisotropic cellulose acylate film is used in the liquid crystal display device, the Rth retardation value of the film is preferably in the range of 150 to 400 nm.
The birefringence (Δn: nx−ny) of the cellulose acylate film is preferably in the range of 0.00 to 0.002. The birefringence {(nx + ny) / 2-nz} in the thickness direction of the cellulose acylate film is preferably in the range of 0.001 to 0.04.
Further, the wavelength dependence of the birefringence of the cellulose acylate film A = Δn (450) / Δn (550) and B = Δn (650) / Δn (550) are 0.20 <A <1.05, And 1.00 <B <1.55.
[0018]
[Prevention of light leakage]
In order to prevent light leakage due to thermal distortion of the liquid crystal display device, the thickness and elastic modulus of the cellulose acylate film are adjusted.
The thickness of the cellulose acylate film is in the range of 10 to 85 μm. The thickness of the cellulose acylate film is preferably as thin as possible, but is preferably 30 μm to 80 μm from the viewpoint of handling in production.
In general, in order to reduce the virtual strain, the plane orientation of polymer molecules is increased by biaxially stretching a cellulose acylate film, or the hygroscopic expansion coefficient is set to 30 × 10. ^-5 /% RH or less is preferable. The hygroscopic expansion coefficient of cellulose acylate film is 15 × 10 ^-5 /% RH or less is more preferable, 10 × 10 ^-5 /% RH or less is most preferable. As a method for suppressing the hygroscopic expansion coefficient, there is a method for increasing the density of the cellulose acylate film.
The elastic modulus of the cellulose acylate film is preferably 3000 MPa or less, and more preferably 2500 MPa or less.
Adjusting the speed of sound so as to satisfy the above-mentioned (iv) and (v) is advantageous from the viewpoint of adjusting the elastic modulus and density and handling in manufacturing.
[0019]
[Cellulose acylate]
Cellulose acylate is an ester of cellulose and acid. The acid is preferably a carboxylic acid, more preferably a fatty acid, still more preferably a fatty acid having 2 to 4 carbon atoms, and most preferably acetic acid (cellulose acetate).
Cellulose acetate having an acetylation degree in the range of 59.0 to 61.5% is particularly 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 viscosity average degree of polymerization (DP) of cellulose acylate is preferably 250 or more, and more preferably 290 or more.
In addition, the cellulose acylate used in the present invention preferably has a narrow molecular weight distribution of Mm / Mn (Mm is a mass average molecular weight and Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mm / Mn is preferably in the range of 1.0 to 1.7, more preferably in the range of 1.3 to 1.65, and in the range of 1.4 to 1.6. Most preferably.
[0020]
[Retardation raising agent]
In order to adjust the retardation of the cellulose acylate film, an aromatic compound having at least two aromatic rings is used as a retardation increasing agent.
The aromatic compound is used in the range of 0.01 to 20 parts by mass with respect to 100 parts by mass of cellulose acylate. 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 the cellulose acylate. 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. It is particularly preferred that the aromatic compound has at least one 1,3,5-triazine ring.
Specific examples of the retardation increasing agent are described in JP-A No. 2002-169023.
By controlling the retardation with a retardation increasing agent, the speed of sound can be controlled within an appropriate range without deformation such as stretching.
[0021]
[Manufacture of cellulose acylate film]
It is preferable to produce a cellulose acylate film by a solvent casting method. In the solvent cast method, a film is produced using a solution (dope) in which cellulose acylate 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.
[0022]
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 the ketone having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.
Examples of the ester 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.
In order to produce the cellulose acylate film according to the present invention, it is preferable to use a mixture of two or more organic solvents. Specifically, from the viewpoint of controlling the speed of sound, it is preferable to use three kinds of solvents, methylene chloride, methanol, and butanol. Methylene chloride is 75 to 85 parts by mass, and methanol is 15 to 25 parts by mass. The parts by mass and butanol are preferably mixed in the range of 0.05 to 5 parts by mass.
[0023]
A cellulose acylate 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.
The amount of cellulose acylate is adjusted so that it is contained in an amount of 10 to 40% by mass in the resulting solution. The amount of cellulose acylate 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 cellulose acylate and an organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, the cellulose acylate and the organic solvent are placed in a pressure vessel and sealed, and stirred while being heated to a temperature equal to or higher 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.
[0024]
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.
[0025]
A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, cellulose acylate 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 cellulose acylate 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, cellulose acylate is gradually added to an organic solvent at room temperature while stirring.
The amount of cellulose acylate is preferably adjusted so as to be contained in the mixture in an amount of 10 to 40% by mass. The amount of cellulose acylate is more preferably 10 to 30% by mass. Furthermore, you may add the arbitrary additive mentioned later in a mixture.
[0026]
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.). When cooled in this way, the mixture of cellulose acylate 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.
[0027]
Furthermore, 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.), cellulose acylate dissolves in the organic solvent. The temperature may be increased 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.
[0028]
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% by mass solution of cellulose cetate (degree of acetylation: 60.9%, viscosity average degree of polymerization: 299) dissolved in methyl acetate by the cooling dissolution method is There is a quasi-phase transition point between a sol state and a gel state in the vicinity of 33 ° C., and a uniform gel state is obtained below this temperature. Therefore, it is necessary to keep this solution at a temperature equal to or higher than the pseudo phase transition temperature, preferably about 10 ° C. plus the gel phase transition temperature. 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.
[0029]
From the prepared cellulose acylate solution (dope), a cellulose acylate film is produced by a solvent cast method. 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. The casting and drying methods in the solvent casting method are described in U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-115035.
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.
[0030]
The obtained film is peeled off from the drum or band, and the residual solvent can be evaporated by drying with hot air with the volatile content of 45 to 70% and successively changing the temperature from 100 ° C. to 160 ° C. The volatile content after stripping is preferably 45 to 70%, more preferably 50 to 65%. When the volatile content is less than 45%, the retardation becomes as large as 20 to 30 nm, and when it exceeds 70%, foaming occurs due to evaporation or film deformation occurs, which causes a problem in any case. The temperature of the warm air is preferably 100 to 160 ° C, and more preferably 110 to 140 ° C. If the temperature is less than 100 ° C., the retardation value becomes large, and if the temperature exceeds 160 ° C., foaming occurs due to evaporation or deformation of the film occurs.
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.
[0031]
Using the prepared cellulose acylate solution (dope), two or more layers can be cast to form a film. In this case, it is preferable to produce a cellulose acylate film by a solvent cast method. 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 in the range of 10 to 40%. The surface of the drum or band is preferably finished in a mirror state.
[0032]
When casting a plurality of cellulose acylate solutions of two or more layers, it is possible to cast a plurality of cellulose acylate solutions, from a plurality of casting openings provided at intervals in the direction of travel of the support. Films can be produced while casting and laminating solutions containing cellulose acylate (for example, as described in JP-A Nos. 61-158414, 1-122419, and 11-198285). ). The film can also be formed by casting a cellulose acylate solution from two casting ports (for example, JP-B-60-27562, JP-A-61-94724, JP-A-61-947245, 61-104813, 61-158413 and JP-A-6-134933). Alternatively, a cellulose acylate film casting method in which a flow of a high viscosity cellulose acylate solution is wrapped with a low viscosity cellulose acylate solution and the high and low viscosity cellulose acylate solution is simultaneously extruded can be used (for example, JP-A 56-162617).
[0033]
In addition, using two casting ports, the film formed on the support by the first casting port is peeled off, and the second casting is performed on the side that is in contact with the support surface to produce the film. A method (for example, described in Japanese Patent Publication No. 44-20235) can also be employed.
As the cellulose acylate solution to be cast, the same solution may be used, or different cellulose acylate solutions may be used. In order to give a function to a plurality of cellulose acylate layers, a cellulose acylate solution corresponding to the function may be extruded from each casting port.
Furthermore, the cellulose acylate solution of the present invention can be cast simultaneously with other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, an ultraviolet absorbing layer, and a polarizing film).
[0034]
In the conventional single-layer solution, it is necessary to extrude a cellulose acylate solution having a high concentration and a high viscosity in order to obtain a necessary film thickness. In such a case, the stability of the cellulose acylate solution is poor and solid matter is generated, which often causes problems due to defects or poor flatness. As a solution to this problem, by casting a plurality of cellulose acylate solutions from the casting port, it is possible to simultaneously extrude a highly viscous solution onto the support, improving the flatness and providing an excellent planar film. Not only can be produced, but also the use of a concentrated cellulose acylate solution can reduce the drying load and increase the production speed of the film.
[0035]
Polyester urethane is preferably added to the cellulose acylate film in order to improve mechanical properties. The polyester urethane is preferably a reaction product of a polyester represented by the following general formula (1) and a diisocyanate, and more preferably soluble in dichloromethane.

In the formula, l represents an integer of 2 to 4; m represents an integer of 2 to 4; and n represents an integer of 1 to 100.
More specifically, in the constituent polyester, the glycol component is ethylene glycol, 1,3-propanediol, or 1,4-butanediol, and the dibasic acid component is succinic acid, glutaric acid, or adipine. It is a polyester having less than both hydroxyl groups consisting of an acid, and its degree of polymerization n is in the range of 1-100. The degree of polymerization n may be in the range of 1 to 100, but the optimum degree of polymerization is slightly different depending on the type of glycol and dibasic acid used, and the molecular weight of the polyester is particularly in the range of 1000 to 4500. preferable.
A dichloromethane-soluble polyester urethane resin is obtained by a reaction of a polyester of the formula (1) and a diisocyanate, and is a compound of a repeating unit represented by the formula (2) as a general formula.
[0036]

In the formula, l represents an integer of 2 to 4; m represents an integer of 2 to 4; n represents an integer of 1 to 100; and R represents a divalent atomic group residue.
Examples of the divalent atomic group residue include those represented by the following formula, for example.
[0037]
[Chemical 1]

[0038]
Examples of the diisocyanate component used in the polyurethane compound include polymethylene diisocyanates represented by ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate and hexamethylene diisocyanate (general formula: OCN -(CH ₂ ) P-NCO (p represents an integer of 2 to 8)), aromatic diisocyanate (for example, p-phenylene diisocyanate, tolylene diisocyanate, p, p'-diphenylmethane diisocyanate, 1, 5-naphthylene diisocyanate) and m-xylylene diisocyanate. Tolylene diisocyanate, m-xylylene diisocyanate and tetramethylene diisocyanate are readily available, relatively stable and easy to handle, and have compatibility with cellulose acylate when polyurethaneized. Since it is excellent, it is preferable.
[0039]
The molecular weight of the polyester urethane resin is preferably in the range of 2000 to 50000. The molecular weight can be appropriately adjusted depending on the type or molecular weight of the component polyesters or diisocyanate component which is a linked group thereof. The molecular weight of the polyester urethane resin is more preferably in the range of 5000 to 15000 in terms of improving the mechanical properties of the cellulose acylate film and compatibility with the cellulose acylate.
The synthesis of dichloromethane-soluble polyester urethane can be easily obtained by mixing polyester diols represented by the formula (1) and diisocyanate and heating with stirring.
The polyester represented by the formula (1) includes a corresponding dibasic acid or an alkyl ester thereof and a hot melt condensation method by a polyesterification reaction or transesterification reaction with a glycol, or an acid chloride of these acids. It can be easily synthesized by appropriately adjusting the terminal group to be a hydroxyl group by any of the interfacial condensation methods with glycols.
The dichloromethane-soluble polyester urethane resin is extremely compatible with cellulose acylate having an acetylation degree of 58% or more. Although a slight difference is recognized depending on the structure of the resin, when the molecular weight of the polyesterurethane is 10,000 or less, even 200 parts by mass of the polyesterurethane is compatible with 100 parts by mass of the cellulose acetate.
[0040]
Therefore, when polyester urethane resin is mixed with cellulose acylate to improve the mechanical properties of the film, the content of polyester urethane resin is appropriately determined according to the type of urethane resin, molecular weight, and desired mechanical properties. Just do it.
In order to improve mechanical properties while maintaining the properties of cellulose acylate, it is preferable to contain 10 to 50% by mass of a polyester urethane resin with respect to cellulose acylate.
The polyester urethane resin is stable up to 180 ° C. and does not thermally decompose. The dichloromethane-soluble polyester urethanes are particularly compatible with cellulose acylate having an acetylation degree of 58% or more. Therefore, when both are formed into a film, a highly transparent film can be obtained. Moreover, since these polyester urethanes have a high average molecular weight, they are hardly volatile even at high temperatures, unlike conventional low-molecular plasticizers. Therefore, the film obtained by forming a film from these mixtures has less inconvenience due to the volatilization and migration of the plasticizer found in the conventional plasticizer in the subsequent processing.
[0041]
By adding polyester urethane to the cellulose acylate film, the bending strength and tear strength at high and low temperatures are increased, and the disadvantage of film tearing is eliminated. Conventionally, low molecular plasticizers have been used to improve the bending strength and tear strength of a film. This method is effective to some extent at room temperature and high humidity, but the film is not flexible at low temperature and high humidity, and satisfactory results are not always obtained. Furthermore, when an attempt was made to improve mechanical properties with a low molecular plasticizer, it was common that the mechanical properties such as tensile strength significantly decreased with the amount of plasticizer added.
When dichloromethane-soluble polyester urethane resin is added to cellulose acylate, a slight decrease in tensile strength is observed with the amount of resin added, but the decrease in strength is clearly small compared to the case of adding a low molecular plasticizer. As a result, a tough film having a high bending strength almost equal to that in the case of no addition can be obtained. Furthermore, by mixing this polyester urethane, it is possible to prevent migration of the plasticizer at low temperature and high humidity. Therefore, it is possible to obtain a transparent and glossy film in which the films do not adhere to each other, are very flexible, and do not wrinkle.
[0042]
In order to improve mechanical properties, it is preferable to add the above polyester urethane to the cellulose acylate film, but the following plasticizers can be used in place of or in combination with the polyester urethane. 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 cellulose ester.
[0043]
A degradation inhibitor (eg, antioxidant, peroxide decomposer, radical inhibitor, metal deactivator, acid scavenger, amine) may be added to the cellulose acylate 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).
[0044]
[Biaxial stretching]
The cellulose acetate film is preferably appropriately stretched to reduce virtual strain. Since the virtual strain in the stretching direction can be reduced by stretching, biaxial stretching is more preferable in order to reduce the strain in all directions in the plane. However, from the viewpoint of handling in manufacturing, it is more preferable to stretch the film so as to be within the above-mentioned sound speed range.
Biaxial stretching includes simultaneous biaxial stretching and sequential biaxial stretching, but sequential biaxial stretching is preferred from the viewpoint of continuous production, and after casting the dope, the film is peeled off from the band or drum, After stretching in the width direction (longitudinal method), the film is stretched in the longitudinal direction (width direction).
Methods for stretching in the width direction are described in, for example, 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 by a treatment during drying, and is particularly effective when the solvent remains. 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 also be stretched by conveying the film while holding it with a tenter and gradually widening the width of 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 in the range of 0 to 50%, more preferably in the range of 10 to 40%, and in the range of 15 to 35%. Most preferably.
[0045]
The process from casting to drying may be performed in an air atmosphere or an inert gas atmosphere such as nitrogen gas. The winder used for producing the cellulose acylate film may be one generally used. For example, it can be wound by a winding method such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress.
[0046]
[Hygroscopic expansion coefficient]
The hygroscopic expansion coefficient indicates the amount of change in the length of the sample when the relative humidity is changed at a constant temperature.
In order to prevent the frame-like transmittance from increasing, the hygroscopic expansion coefficient of the cellulose acylate film is 30 × 10 ^-5 /% RH or less, preferably 15 × 10 ^-5 /% RH or less is more preferable, 10 × 10 ^-5 /% RH or less is most preferable. The hygroscopic expansion coefficient is preferably small, but usually 1.0 × 10 ^-5 /% RH or more.
The method for measuring the hygroscopic expansion coefficient is shown below. A sample having a width of 5 mm and a length of 20 mm was cut out from the produced polymer film (retardation plate), one end was fixed, and the sample was hung in an atmosphere of 25 ° C. and 20% RH (R0). A weight of 0.5 g was hung from the other end and left for 10 minutes to measure the length (L0). Next, the length (L1) was measured while maintaining the temperature at 25 ° C. and the humidity at 80% RH (R1). The hygroscopic expansion coefficient was calculated by the following equation. The measurement was performed 10 samples for the same sample, and the average value was adopted.
Hygroscopic expansion coefficient [/% RH] = {(L1-L0) / L0} / (R1-R0)
[0047]
It has been found that the dimensional change due to moisture absorption can 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 general method for reducing the residual solvent is to dry at a high temperature for a long time. However, if the time is too long, the productivity is naturally lowered. Accordingly, the amount of the residual solvent relative to the cellulose acylate 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%. The most preferable range is 0.05 mass%.
By controlling the amount of the residual solvent, a polarizing plate having optical compensation ability can be produced at low cost with high productivity.
[0048]
The amount of residual solvent means the amount of volatile matter with respect to solid mass, and is defined by the following formula.
Residual solvent amount (% by mass) = ((W−W0) / W0) × 100
W: Mass of sample buffy coat
W0: Sample mass after drying the sample buffy coat at 110 ° C. for 2 hours
The amount of residual solvent was measured using a gas chromatograph (GC18A, manufactured by Shimadzu Corporation) by dissolving a certain amount of sample in chloroform.
[0049]
In the solution casting method, a film is produced using a solution (dope) in which a polymer material is dissolved in an organic solvent. As will be described later, drying by the solution casting method is largely divided into drying on the drum (or band) surface and drying during film conveyance. When drying on the drum (or band) surface, it is preferable to dry slowly at a temperature that does not exceed the boiling point of the solvent being used (when the boiling point is exceeded, bubbles are formed).
In order to realize the cellulose acylate film of the present invention, it is important to warm the drum (or band) immediately after peeling. The heating temperature is preferably 110 ° C. to 160 ° C., more preferably 120 ° C. to 150 ° C.
Further, it is preferable that drying during film transportation is performed at a glass transition point of the polymer material ± 30 ° C., more preferably ± 20 ° C.
[0050]
Further, as another method for reducing the dimensional change due to moisture absorption, it is preferable to add a compound having a hydrophobic group. The material having a hydrophobic group is not particularly limited as long as it is a material having a hydrophobic group such as an alkyl group or a phenyl group in the molecule. Among the plasticizers and deterioration inhibitors added to the cellulose acylate film, In particular, the corresponding material is preferably used. Examples thereof 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, more preferably in the range of 0.1 to 5% by mass with respect to the solution (dope) to be adjusted. It is preferably in the range of 1 to 3% by mass.
[0051]
[Surface treatment of cellulose acylate film]
The cellulose acylate film is preferably subjected to a surface treatment. Specific examples include corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment, and ultraviolet irradiation treatment. It is also preferable to provide an undercoat layer (for example, described in JP-A-7-333433).
From the viewpoint of maintaining the flatness of the film, the temperature of the cellulose acylate film in these treatments is preferably Tg (glass transition temperature) or lower, specifically 150 ° C. or lower.
When used as a transparent protective film for a polarizing plate, it is particularly preferable to carry out acid treatment or alkali treatment, that is, saponification treatment for cellulose acylate, from the viewpoint of adhesiveness to the polarizing film.
The surface energy is preferably 55 mN / m or more, and more preferably 60 mN / m or more and 75 mN / m or less.
[0052]
Hereinafter, a particularly preferable alkali saponification treatment will be specifically described.
The alkali saponification treatment of the cellulose acylate film is preferably performed in a cycle in which the film surface is immersed in an alkali solution, neutralized with an acidic solution, washed with water and dried.
Examples of the alkaline solution include potassium hydroxide solution and 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 it is. 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.
[0053]
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 the cellulose acylate film of the present invention, the contact angle method is preferably used.
Specifically, two types of solutions having known surface energies are dropped on a cellulose acylate 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.
[0054]
The optical compensation sheet can be provided with an optically anisotropic layer formed from a liquid crystalline compound on the produced cellulose acylate film. An alignment film is preferably provided between the cellulose acylate film and the optically anisotropic layer provided thereon. The alignment film functions to align the liquid crystalline compound used in the present invention in a certain direction. Therefore, the alignment film is essential for producing the optical compensation sheet of the present invention. However, if the alignment state is fixed after aligning the liquid crystalline compound, the alignment film plays the role, and thus is not necessarily an essential component of the optical compensation sheet. That is, it is possible to produce an optical compensation sheet by transferring only the optically anisotropic layer on the alignment film in which the alignment state is fixed onto the cellulose acylate film.
[0055]
[Alignment film]
The alignment film has a function of defining the alignment direction of the liquid crystalline compound. 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. The alignment film is preferably formed by polymer rubbing treatment.
[0056]
The alignment film is preferably formed by polymer rubbing treatment. Polyvinyl alcohol is a preferred polymer. Particularly preferred is a modified polyvinyl alcohol to which a hydrophobic group is bonded.
The alignment film can be formed from one type of polymer, but is more preferably formed by rubbing a layer composed of two types of crosslinked polymers. As the at least one polymer, it is preferable to use either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent.
The alignment film is formed by reacting a polymer having a functional group or a polymer into which a functional group is introduced by polymerizing the polymer by light, heat, pH change, or the like; or a cross-linking agent that is a compound having high reaction activity Can be formed by introducing a linking group derived from a cross-linking agent between polymers to cross-link between the polymers.
[0057]
Such crosslinking is carried out by applying an alignment film coating solution containing the polymer or a mixture of a polymer and a crosslinking agent on a cellulose acylate film, followed by heating. Since it is only necessary to ensure the durability of the final product (optical compensation sheet), crosslinking may be performed at any stage after the alignment film is coated on the cellulose acylate film until the optical compensation sheet is obtained. .
Considering the orientation of the liquid crystal compound layer (optically anisotropic layer) formed on the alignment film, it is also preferable to sufficiently crosslink after aligning the liquid crystal compound.
In general, the alignment film is crosslinked by applying an alignment film coating solution on a cellulose acylate film and drying by heating. It is preferable that the heating temperature of the coating solution is set low so that the alignment film is sufficiently cross-linked at the stage of the heat treatment when forming the optically anisotropic layer described later.
[0058]
As the polymer used for the alignment film, either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent can be used. Of course, some polymers are possible. Examples of polymers include polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleimide copolymer, polyvinyl alcohol and modified polyvinyl alcohol, poly (N-methylol acrylamide), styrene / vinyl toluene copolymer, Mention may be made of chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, carboxymethyl cellulose, polyethylene, polypropylene and polycarbonate. . A silane coupling agent can be used in place of the polymer.
Preferred polymers are water-soluble polymers (eg, poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol, modified polyvinyl alcohol). Gelatin, polyvinyl alcohol and modified polyvinyl alcohol are preferred, and polyvinyl alcohol and modified polyvinyl alcohol are more preferred.
It is most preferable to use two types of polyvinyl alcohol or modified polyvinyl alcohol having different degrees of polymerization.
[0059]
Polyvinyl alcohol preferably has a saponification degree in the range of 70 to 100%. The saponification degree is more preferably in the range of 80 to 100%, and further preferably in the range of 85 to 95%. The polymerization degree of polyvinyl alcohol is preferably in the range of 100 to 3000.
Examples of the modified polyvinyl alcohol include polyvinyl alcohol modified by copolymerization, modification by chain transfer, or modification by block polymerization. Examples of modifying groups in the case of copolymerization modification include COONa, Si (OX) ₃ , N (CH ₃ ) ₃ ・ Cl, C ₉ H ₁₉ COO, SO ₃ Na, C ₁₂ H ₂₅ Is mentioned. Examples of modifying groups for modification by chain transfer include COONa, SH, C ₁₂ H ₂₅ Is mentioned. Examples of modifying groups in the case of modification by block polymerization include COOH, CONH ₂ , COOR, C ₆ H ₅ Is mentioned.
Unmodified or modified polyvinyl alcohol having a saponification degree in the range of 80 to 100% is preferred. More preferred are unmodified polyvinyl alcohol and modified polyvinyl alcohol having a saponification degree in the range of 85 to 95%.
[0060]
As the modified polyvinyl alcohol, it is particularly preferable to use a modified product of polyvinyl alcohol by a compound represented by the following general formula. Hereinafter, this modified polyvinyl alcohol is referred to as a specific modified polyvinyl alcohol.
[0061]
[Chemical 2]

[0062]
Where R ¹ Represents an alkyl group, an acryloylalkyl group, a methacryloylalkyl group, or an epoxyalkyl group; W represents a halogen atom, an alkyl group, or an alkoxy group; X represents an active ester, an acid anhydride, or an acid halide. Represents a group of atoms necessary to form; p represents 0 or 1; and n represents an integer of 0 to 4.
The specific modified polyvinyl alcohol is preferably a modified product of polyvinyl alcohol with a compound represented by the following general formula.
[0063]
[Chemical 3]

[0064]
Where X ¹ Represents an atomic group necessary to form an active ester, an acid anhydride, or an acid halide, and m represents an integer of 2 to 24.
[0065]
Examples of the polyvinyl alcohol used for reacting with the compounds represented by these general formulas include the above-mentioned unmodified polyvinyl alcohol and those modified by copolymerization, that is, modified by chain transfer, modified by block polymerization. A modified product of polyvinyl alcohol, such as those obtained. Preferred examples of specific modified polyvinyl alcohol are described in JP-A-9-152509.
Japanese Patent Application Laid-Open No. 8-338913 discloses a method for synthesizing these polymers, a method for measuring a visible absorption spectrum, a method for determining a modification group introduction rate, and the like.
[0066]
Examples of crosslinking agents include aldehydes, N-methylol compounds, dioxane derivatives, compounds that act by activating carboxyl groups, active vinyl compounds, active halogen compounds, isoxazoles, and dialdehyde starch. it can. Examples of aldehydes include formaldehyde, glyoxal, and glutaraldehyde. Examples of N-methylol compounds include dimethylol urea and methylol dimethyl hydantoin. Examples of dioxane derivatives 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). Can be mentioned. Examples of active vinyl compounds include 1,3,5-triacroyl-hexahydro-s-triazine, bis (vinylsulfone) methane, and N, N′-methylenebis- [β- (vinylsulfonyl) propionamide]. . An example of the active halogen compound is 2,4-dichloro-6-hydroxy-S-triazine. These can be used in combination.
These are preferable when used in combination with the above water-soluble polymer, particularly polyvinyl alcohol and modified polyvinyl alcohol (including the above-mentioned specific modified products). In view of productivity, it is preferable to use an aldehyde having a high reaction activity, particularly glutaraldehyde.
[0067]
The moisture resistance tends to be improved by adding more crosslinking agent. However, when the crosslinking agent is added in an amount of 50% by mass or more based on the polymer, the alignment ability as the alignment film is lowered. Accordingly, the amount of the crosslinking agent added to the polymer is preferably in the range of 0.1 to 20% by mass, and more preferably in the range of 0.5 to 15% by mass. The alignment film contains a certain amount of the crosslinking agent that has not reacted even after the crosslinking reaction is completed. The amount of the crosslinking agent is preferably 1.0% by mass or less in the alignment film. More preferably, it is 5 mass% or less. If the alignment film contains an unreacted crosslinking agent in an amount exceeding 1.0% by mass, sufficient durability cannot be obtained. That is, when used in a liquid crystal display device, reticulation may occur when used for a long time or when left in a high temperature and high humidity atmosphere for a long time.
[0068]
The alignment film can be formed by applying a solution containing the polymer or a solution containing the polymer and a crosslinking agent onto a cellulose acylate film, followed by drying by heating (crosslinking) and rubbing treatment. The cross-linking reaction may be performed at any time after the coating solution is applied on the cellulose acylate film.
When a water-soluble polymer such as polyvinyl alcohol is used as the alignment film forming material, the solvent for preparing the coating solution is an organic solvent such as methanol having a defoaming action, or a mixture of an organic solvent and water. It is preferable to use a solvent. When methanol is used as the organic solvent, the mass ratio of water: methanol is generally 0: 100 to 99: 1, and more preferably 0: 100 to 91: 9. Thereby, generation | occurrence | production of a bubble is suppressed and the defect of the surface of an alignment film and also an optical anisotropic layer reduces remarkably.
Examples of the coating method include a spin coating method, a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method, and an E type coating method. The E-type coating method is particularly preferable.
[0069]
The thickness of the alignment film is preferably in the range of 0.1 to 10 μm. The heat drying can be performed at a heating temperature in the range of 20 to 110 ° C. In order to form sufficient crosslinking, the heating temperature is preferably in the range of 60 to 100 ° C, and more preferably in the range of 80 to 100 ° C. The drying time can be 1 minute to 36 hours. Preferably it is 5 to 30 minutes. The pH is also preferably set to an optimum value for the cross-linking agent to be used. When glutaraldehyde is used, it is preferably in the range of pH 4.5 to 5.5, particularly preferably pH 5.
[0070]
For the rubbing treatment, a treatment method widely adopted as a liquid crystal alignment treatment process of the LCD can be used. That is, a method of obtaining alignment by rubbing the surface of the alignment film in a certain direction using paper, gauze, felt, rubber, nylon, polyester fiber or the like can be used. In general, it is carried out by rubbing several times using a cloth in which fibers having a uniform length and thickness are flocked on average.
[0071]
[Optically anisotropic layer]
An optically anisotropic layer formed from a liquid crystalline compound can be formed on an alignment film provided on a cellulose acylate film.
The liquid crystalline compound used for the optically anisotropic layer includes a rod-like liquid crystalline compound and a discotic liquid crystalline compound. The rod-like liquid crystal compound and the discotic liquid crystal compound may be a polymer liquid crystal or a low-molecular liquid crystal, and further include those in which the low-molecular liquid crystal is cross-linked and no longer exhibits liquid crystallinity.
The optically anisotropic layer can be formed by applying a liquid crystal compound and, if necessary, a coating liquid containing a polymerizable initiator and optional components on the alignment film.
[0072]
As a solvent used for adjusting 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, tetrachloroethane), 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.
The coating liquid can be applied by a known method (eg, wire bar coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).
The thickness of the optically anisotropic layer is preferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, and most preferably 1 to 10 μm.
[0073]
Examples of rod-like liquid crystalline compounds 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 compound includes a metal complex. Moreover, the liquid crystal polymer which contains a rod-shaped liquid crystalline compound in a repeating unit can also be used as a rod-shaped liquid crystalline compound. In other words, the rod-like liquid crystalline compound may be bonded to a (liquid crystal) polymer.
For rod-like liquid crystalline compounds, see Chapter 4, Chapter 7 and Chapter 11 of the Chemistry of the Quarterly Chemical Review Vol. 22 Liquid Crystal Chemistry (1994) edited by the Chemical Society of Japan, and the 142nd Committee of the Japan Society for the Promotion of Science. Described in Chapter 3.
The birefringence of the rod-like liquid crystalline compound is preferably in the range of 0.001 to 0.7.
The rod-like liquid crystalline compound preferably has a polymerizable group in order to fix its alignment state. Examples of the polymerizable group (Q) are shown below.
[0074]
[Formula 4]

[0075]
[Chemical formula 5]

[0076]
[Chemical 6]

[0077]
[Chemical 7]

[0078]
[Chemical 8]

[0079]
[Chemical 9]

[0080]
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).
The rod-like liquid crystalline compound preferably has a molecular structure that is substantially symmetrical with respect to the minor axis direction. For that purpose, it is preferable to have a polymerizable group at both ends of the rod-like molecular structure.
Below, the example of a rod-shaped liquid crystalline compound is shown.
[0081]
Embedded image

[0082]
Embedded image

[0083]
Embedded image

[0084]
Embedded image

[0085]
Embedded image

[0086]
Embedded image

[0087]
Embedded image

[0088]
Embedded image

[0089]
Embedded image

[0090]
Embedded image

[0091]
Embedded image

[0092]
Embedded image

[0093]
Embedded image

[0094]
Embedded image

[0095]
Embedded image

[0096]
Embedded image

[0097]
Embedded image

[0098]
Embedded image

[0099]
Embedded image

[0100]
Embedded image

[0101]
Embedded image

[0102]
Embedded image

[0103]
Embedded image

[0104]
Embedded image

[0105]
Embedded image

[0106]
Embedded image

[0107]
Embedded image

[0108]
Embedded image

[0109]
Embedded image

[0110]
Embedded image

[0111]
Embedded image

[0112]
Embedded image

[0113]
Embedded image

[0114]
Embedded image

[0115]
Embedded image

[0116]
Embedded image

[0117]
Embedded image

[0118]
Embedded image

[0119]
Embedded image

[0120]
Embedded image

[0121]
Embedded image

[0122]
Embedded image

[0123]
Embedded image

[0124]
Embedded image

[0125]
Embedded image

[0126]
Embedded image

[0127]
Embedded image

[0128]
The optically anisotropic layer is composed of a rod-like liquid crystalline compound or a polymerization initiator or an optional additive described later (eg, plasticizer, monomer, surfactant, cellulose ester, 1,3,5-triazine compound, chiral agent). It can form by apply | coating the liquid crystal composition (coating liquid) containing this on alignment film.
[0129]
Examples of discotic liquid crystalline compounds include C.I. Destrade et al., Mol. Cryst. 71, 111 (1981), benzene derivatives described in C.I. Destrade et al., Mol. Cryst. 122, 141 (1985), Physics lett, A, 78, 82 (1990); Kohne et al., Angew. Chem. 96, page 70 (1984) and the cyclohexane derivatives described in J. Am. M.M. Lehn et al. Chem. Commun. , 1794 (1985), J. Am. Zhang et al., J. Am. Chem. Soc. 116, 2655 (1994), and azacrown and phenylacetylene macrocycles. Furthermore, the discotic liquid crystalline compounds generally have a structure in which these are used as a mother nucleus at the center of a molecule, and a linear alkyl group, an alkoxy group, a substituted benzoyloxy group, etc. are radially substituted as the linear chain. Is also included and exhibits liquid crystallinity. In the present invention, the optically anisotropic layer formed from the discotic liquid crystalline compound does not necessarily need to be the final compound. For example, a low molecular weight discotic liquid crystalline compound is formed by heat or light. In other words, the polymer may be polymerized or cross-linked by reaction with heat, light or the like, resulting in high molecular weight and loss of liquid crystallinity. Preferred examples of the discotic liquid crystalline compound are described in JP-A-8-50206. The polymerization of the discotic liquid crystalline compound is described in JP-A-8-27284.
[0130]
In order to fix the discotic liquid crystalline compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline compound. 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. Therefore, the discotic liquid crystalline compound having a polymerizable group is preferably a compound represented by the following formula (III).
[0131]
(III) 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.
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).
[0132]
Embedded image

[0133]
Embedded image

[0134]
Embedded image

[0135]
Embedded image

[0136]
Embedded image

[0137]
Embedded image

[0138]
Embedded image

[0139]
Embedded image

[0140]
Embedded image

[0141]
In the formula (III), 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.
[0142]
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-
[0143]
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-
[0144]
The polymerizable group (Q) of the formula (III) is the same as the polymerizable group (Q) described for the rod-like liquid crystal compound.
In the formula (III), 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.
[0145]
When a discotic liquid crystalline compound is used, the optically anisotropic layer is a layer having negative birefringence, and the plane of the discotic structural unit is inclined with respect to the cellulose acylate film surface, and the discotic structural unit. It is preferable that the angle formed between this surface and the cellulose acylate film surface changes in the depth direction of the optically anisotropic layer.
[0146]
The surface angle (tilt angle) of the disk-like structural unit generally increases or decreases in the depth direction of the optically anisotropic layer and with an increase in the distance from the bottom surface of the optically anisotropic layer. The tilt angle preferably increases with increasing distance. In addition, changes in the inclination angle include continuous increase, continuous decrease, intermittent increase, intermittent decrease, change including continuous increase and continuous decrease, and intermittent change including increase and decrease. it can. The intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction. Even if the tilt angle includes a region where the tilt angle does not change, the tilt angle preferably increases or decreases as a whole. Further, the inclination angle is preferably increased as a whole, and particularly preferably continuously changed.
[0147]
The inclination angle of the disk-shaped unit on the support side can be adjusted by selecting a disk-shaped liquid crystalline compound or a material for the alignment film, or by selecting a rubbing treatment method. Further, the inclination angle of the disk-like unit on the surface side (air side) can be adjusted by selecting a discotic liquid crystalline compound or another compound used together with the discotic liquid crystalline compound. Examples of the compound used together with the discotic liquid crystalline compound include a plasticizer, a surfactant, a polymerizable monomer and a polymer. Further, the degree of change in the tilt angle can be adjusted by the same selection as described above.
[0148]
The plasticizer, surfactant, and polymerizable monomer used together with the discotic liquid crystalline compound are compatible with the discotic liquid crystalline compound and can change the tilt angle of the discotic liquid crystalline compound or can be aligned. Any compound can be used as long as it does not inhibit Among these, polymerizable monomers (eg, compounds having a vinyl group, a vinyloxy group, an acryloyl group, and a methacryloyl group) are preferable. The amount of the compound added is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the discotic liquid crystalline compound.
[0149]
As the polymer used together with the discotic liquid crystalline compound, any polymer can be used as long as it is compatible with the discotic liquid crystalline compound and can change the tilt angle of the discotic liquid crystalline compound. A cellulose ester can be mentioned as an example of a polymer. Preferred examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose, and cellulose acetate butyrate. In order not to inhibit the alignment of the discotic liquid crystalline compound, the amount of the polymer added is generally in the range of 0.1 to 10% by mass, and in the range of 0.1 to 8% by mass with respect to the discotic liquid crystalline compound. More preferably, it is in the range of 0.1 to 5% by mass.
[0150]
The optically anisotropic layer is generally formed by applying a solution obtained by dissolving a discotic liquid crystalline compound and other compounds in a solvent onto an alignment film, drying it, and then heating it to a discotic nematic phase formation temperature, and then aligning it (disco It can be obtained by cooling while maintaining the (tick nematic phase). Alternatively, the optically anisotropic layer is formed by applying a solution obtained by dissolving a discotic liquid crystalline compound and another compound (for example, a polymerizable monomer, a photopolymerization initiator) in a solvent onto the alignment film, and then drying, It is obtained by heating to a discotic nematic phase formation temperature, polymerizing (by irradiation with UV light or the like), and further cooling. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound is preferably 70 to 300 ° C, more preferably 70 to 170 ° C.
[0151]
[Fixation of alignment state of liquid crystalline compound]
The aligned liquid crystalline compound can be fixed while maintaining the alignment state. The immobilization is preferably performed by a polymerization reaction. 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 substitution 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 Patent No. 3549367), acridine and phenazine compounds (JP-A-60-105667, US Pat. No. 4,239,850) and oxadiazole compounds (US Pat. No. 4,221,970) are included. .
The amount of the photopolymerization initiator used is preferably in the range of 0.01 to 20% by mass, more preferably in the range of 0.5 to 5% by mass, based on the solid content of the coating solution.
Light irradiation for the polymerization of the liquid crystalline compound is preferably performed using ultraviolet rays.
Irradiation energy is 20mJ / cm ² ~ 50J / cm ² Is preferably in the range of 20 to 5000 mJ / cm. ² More preferably, it is in the range of 100 to 800 mJ / cm. ² It is most preferable that it exists in the range. 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.
[0152]
[Polarizer]
A polarizing plate consists of a polarizing film and two transparent protective films arrange | positioned at the both sides. As one protective film, the above optical compensation sheet can be used. A normal cellulose acetate film may be used for the other protective film.
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.
[0153]
It was also found that the moisture permeability of the protective film is important for the productivity of the polarizing plate. The polarizing film and the protective film are bonded together with a water-based adhesive, and the adhesive solvent is dried by diffusing in the protective film. The higher the moisture permeability of the protective film, the faster the drying and the higher the productivity. However, if the protective film is too high, moisture will enter the polarizing film depending on the usage environment (high humidity) of the liquid crystal display device. Polarization ability decreases.
The moisture permeability of the optical compensation sheet is determined by the thickness, free volume, hydrophilicity / hydrophobicity, etc. of the polymer film (and polymerizable liquid crystal compound).
When the optical compensation sheet is used as a protective film for a polarizing plate, the moisture permeability of the optical compensation sheet is 100 to 1000 (g / m ² ) / 24 hrs, preferably 300 to 700 (g / m ² ) / 24 hrs.
[0154]
The thickness of the optical compensation sheet can be adjusted by the lip flow rate and the line speed, or stretching and compression when the cellulose acylate film is formed. Since the moisture permeability varies depending on the main material to be used, it is possible to make a preferable range by adjusting the thickness.
In the case of film formation, the free volume of the optical compensation sheet can be adjusted by the drying temperature and time. Also in this case, moisture permeability varies depending on the main material to be used, so that a preferable range can be obtained by adjusting the free volume.
The hydrophilicity / hydrophobicity of the optical compensation film can be adjusted by an additive. Moisture permeability is increased by adding a hydrophilic additive in the free volume, and conversely, moisture permeability can be lowered by adding a hydrophobic additive.
By adjusting the moisture permeability of the optical compensation sheet, it becomes possible to produce a polarizing plate having optical compensation ability at low cost with high productivity.
[0155]
[Liquid Crystal Display]
A polarizing plate obtained by bonding an optical compensation sheet or an optical compensation sheet and a polarizing film is advantageously used for 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. A polarizing plate consists of a polarizing film and two transparent protective films arrange | positioned at the both sides. The liquid crystal cell carries a liquid crystal between two electrode substrates.
One optical compensation sheet of the present invention is disposed between the liquid crystal cell and one polarizing plate, or two optical compensation sheets are disposed between the liquid crystal cell and both polarizing plates.
The polarizing plate of the present invention may be used as at least one of the two polarizing plates arranged on both sides of the liquid crystal cell. In this case, the polarizing plate of the present invention is arranged so that the optical compensation sheet is on the liquid crystal cell side.
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.
[0156]
【Example】
[Example 1]
(Preparation of cellulose acylate film)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acylate solution.
[0157]
────────────────────────────────────
Cellulose acylate 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
295 parts by mass of methylene chloride (first solvent)
Methanol (second solvent) 68 parts by mass
1-butanol (third solvent) 2 parts by mass
───────────────────────────────────
[0158]
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.
[0159]
Embedded image

[0160]
A dope was prepared by mixing 474 parts by mass of the cellulose acylate solution with 25 parts by mass of the retardation increasing agent solution and stirring sufficiently. The addition amount of the retardation increasing agent was 3.5 parts by mass with respect to 100 parts by mass of cellulose acetate.
The obtained dope was cast using a drum casting machine. After the film surface temperature on the drum reaches 40 ° C, it is dried with warm air of 70 ° C for 1 minute, and the film is peeled off from the drum with the volatile content of 55%. Immediately after that, the film is dried at 140 ° C. Ring drying with wind for 1 minute, and further drying with 130 ° C. drying air for 15 minutes, a cellulose acylate film (thickness: 80 μm) having a residual solvent amount of 0.3 mass% was produced.
Optical characteristics of the produced cellulose acylate film (CAF-01) were measured. The results are shown in Table 1.
In addition, the optical property measured the Re retardation value and Rth retardation value in wavelength 550nm using the ellipsometer (M-150, JASCO Corporation make).
The produced cellulose acylate film was immersed in a 2.0N potassium hydroxide solution (25 ° C.) for 2 minutes, neutralized with sulfuric acid, washed with pure water and dried. The surface energy of this cellulose acylate film was determined by a contact angle method and found to be 63 mN / m.
[0161]
(Formation of alignment film)
On the produced cellulose acylate film, a coating solution having the following composition was 28 ml / m with a # 16 wire bar coater ² Applied. 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 parallel to the longitudinal direction of the cellulose acylate film.
[0162]
────────────────────────────────────
Alignment film coating solution composition
────────────────────────────────────
10 parts by mass of the following modified polyvinyl alcohol
371 parts by weight of water
119 parts by mass of methanol
Glutaraldehyde (crosslinking agent) 0.5 parts by mass
────────────────────────────────────
[0163]
Embedded image

[0164]
(Formation of optically anisotropic layer)
On the alignment film, 41.01 g of the following discotic liquid crystalline compound, 4.06 g of ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), cellulose acetate butyrate (CAB551-0. 2, Eastman Chemical Co.) 0.90 g, cellulose acetate butyrate (CAB531-1, Eastman Chemical Co.) 0.23 g, photopolymerization initiator (Irgacure 907, Ciba Geigy Co.) 1.35 g, sensitization A coating solution prepared by dissolving 0.45 g of an agent (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 102 g of methyl ethyl ketone was applied with a # 3.6 wire bar. This was heated in a constant temperature zone of 130 ° C. for 2 minutes to align the discotic liquid crystalline compound. Next, UV irradiation was performed for 1 minute using a 120 W / cm high pressure mercury lamp in an atmosphere of 60 ° C. to polymerize the discotic liquid crystalline compound. Then, it stood to cool to room temperature. Thus, an optically anisotropic layer was formed, and an optical compensation sheet (KH-01) was produced.
[0165]
Embedded image

[0166]
The Re retardation value of the optically anisotropic layer measured at a wavelength of 546 nm was 43 nm. The angle (tilt angle) between the disk surface and the transparent support (cellulose acylate film) surface was 42 ° on average.
[0167]
[Example 2]
(Preparation of cellulose acylate film)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acylate solution.
[0168]
────────────────────────────────────
Cellulose acylate solution composition
────────────────────────────────────
100 parts by mass of cellulose acetate having an acetylation degree of 60.7%
16 parts by mass of polyether urethane
(B-326, Sumitomo Bayer Urethane Co., Ltd., Desmocol 176)
290 parts by mass of methylene chloride (first solvent)
Methanol (second solvent) 73 parts by mass
1-butanol (third solvent) 2 parts by mass
────────────────────────────────────
[0169]
In another mixing tank, 16 parts by mass of the retardation increasing agent used in Example 1, 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.
A dope was prepared by mixing 484 parts by mass of the cellulose acylate solution with 15 parts by mass of the retardation increasing agent solution and stirring sufficiently. The addition amount of the retardation increasing agent was 2.0 parts by mass with respect to 100 parts by mass of cellulose acetate.
[0170]
The obtained dope was cast using a drum casting machine. After the film surface temperature on the drum reached 40 ° C., the film was dried with warm air of 65 ° C. for 1 minute, and the film having a residual solvent of 60% was peeled off from the drum. Next, while the film was stretched 20% in the width direction with a tenter, the film was dried with a drying air at 130 ° C. for 5 minutes to make the residual solvent amount 5% by mass. In this state, the film was stretched 18% in the longitudinal direction, and further dried at 140 ° C. for 10 minutes to produce a cellulose acylate film (thickness: 40 μm) having a residual solvent of 0.3% by mass.
The optical properties of the produced cellulose acylate film (CAF-02) were measured. The results are shown in Table 1.
In addition, the optical property measured the Re retardation value and Rth retardation value in wavelength 550nm using the ellipsometer (M-150, JASCO Corporation make).
In the same manner as in Example 1, the cellulose acylate film was subjected to a surface treatment to form an alignment film and an optically anisotropic layer, thereby producing an optical compensation sheet (KH-02).
[0171]
[Comparative Example 1]
(Preparation of cellulose acylate film)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acylate solution.
[0172]
────────────────────────────────────
Cellulose acylate 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
────────────────────────────────────
[0173]
This cellulose acylate solution was directly used as a dope and cast using a band casting machine. After the film surface temperature on the band reached 40 ° C., the film was dried with warm air of 40 ° C. for 1 minute, and the film was peeled off from the band with a volatile content of 30%. Next, the film was dried with a drying air at 100 ° C. for 30 minutes to produce a cellulose acylate film (thickness: 80 μm) having a residual solvent amount of 0.9% by mass.
The optical properties of the produced cellulose acylate film (CAF-H1) were measured. The results are shown in Table 1.
[0174]
[Table 1]

Note: The speed of sound was measured using an SST-2500 model manufactured by Nomura Corporation.
[0175]
[Example 4]
A polarizing film is prepared by adsorbing iodine to a stretched polyvinyl alcohol film, and the optical compensation sheet (KH-01) prepared in Example 1 is cellulose acylate film (CAF-01) using a polyvinyl alcohol-based adhesive. Is attached to one side of the polarizing film so that is on the polarizing film side. The transmission axis of the polarizing film and the slow axis of the optical compensation sheet (KH-01) were arranged in parallel.
A commercially available cellulose triacetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. In this way, a polarizing plate was produced.
[0176]
[Example 5]
A polarizing film is prepared by adsorbing iodine to a stretched polyvinyl alcohol film, and the optical compensation sheet (KH-02) prepared in Example 2 is cellulose acylate film (CAF-02) using a polyvinyl alcohol-based adhesive. Is attached to one side of the polarizing film so that is on the polarizing film side. The transmission axis of the polarizing film and the slow axis of the optical compensation sheet (KH-02) were arranged in parallel.
A commercially available cellulose triacetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. In this way, a polarizing plate was produced.
[0177]
[Comparative Example 2]
A polarizing film was prepared by adsorbing iodine to the stretched polyvinyl alcohol film, and the cellulose acylate film prepared in Comparative Example 1 was attached to one side of the polarizing film using a polyvinyl alcohol-based adhesive. The transmission axis of the polarizing film and the slow axis of the cellulose acylate film (CAF-H1) were arranged to be perpendicular.
A commercially available cellulose triacetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. In this way, a polarizing plate was produced.
[0178]
[Example 7]
A pair of polarizing plates provided in a liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN type liquid crystal cell is peeled off, and the polarizing plate produced in Example 4 is replaced with an optical compensation sheet (KH). One sheet was affixed to the viewer side and the backlight side through an adhesive so that -01) was on the liquid crystal cell side. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be orthogonal to each other.
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). The results are shown in Table 2.
[0179]
[Example 8]
A pair of polarizing plates provided in a liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN type liquid crystal cell is peeled off, and the polarizing plate produced in Example 5 is replaced with an optical compensation sheet (KH). -02) was pasted to the viewer side and the backlight side one by one through the adhesive so that the liquid crystal cell side would be. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be orthogonal to each other.
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). The results are shown in Table 2.
[0180]
[Comparative Example 3]
About a liquid crystal display device (6E-A3, manufactured by Sharp Corporation) using a TN liquid crystal cell, from a black display (L1) to a white display (L8) using a measuring device (EZ-Contrast 160D, manufactured by ELDIM) The viewing angle was measured in 8 stages. The results are shown in Table 2.
[0181]
[Table 2]

(Ii) Black-side gradation inversion: inversion between L1 and L2
[0182]
[Example 10]
A pair of polarizing plates provided in a 20-inch liquid crystal display device (LC-20V1, manufactured by Sharp Corporation) using a TN type liquid crystal cell is peeled off, and the polarizing plate produced in Example 4 is optically compensated instead. The sheets (KH-01) were attached to the observer side and the backlight side one by one through an adhesive so that the sheet (KH-01) was on the liquid crystal cell side. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be orthogonal to each other.
Under environmental conditions of a temperature of 25 ° C. and a relative humidity of 60%, the backlight was lit continuously for 5 hours, and the entire black display state was visually observed in a dark room to evaluate light leakage. As a result, no light leakage was observed on the display screen of the liquid crystal display device.
[0183]
[Example 11]
A polarizing plate was mounted on a liquid crystal display device in the same manner as in Example 10 except that the polarizing plate produced in Example 5 was used.
Light leakage was evaluated in the same manner as in Example 10. As a result, no light leakage was observed on the display screen of the liquid crystal display device.
[0184]
[Comparative Example 4]
A polarizing plate was mounted on a liquid crystal display device in the same manner as in Example 10 except that the polarizing plate prepared in Comparative Example 2 was used.
Light leakage was evaluated in the same manner as in Example 10. As a result, frame-like light leakage was observed on the display screen of the liquid crystal display device.

Claims (8)

An optical compensation sheet comprising a cellulose acylate film, wherein the cellulose acylate film has an in-plane retardation value in the range of 0 to 20 nm, a thickness in the range of 10 to 85 μm, and a range of 2.2 to 2.5 km / sec. The average of the minimum and maximum sound speeds measured in the film plane, and the ratio of the maximum value to the minimum sound speed measured in the film plane in the range of 1.01 to 1.12. Optical compensation sheet. An optical compensation sheet comprising an optically anisotropic layer formed of a cellulose acylate film and a liquid crystal compound, wherein the cellulose acylate film has an in-plane retardation value in the range of 0 to 20 nm and a range of 10 to 85 μm. Thickness, average of minimum and maximum sound speed measured in the film plane in the range of 2.2 to 2.5 km / sec, and sound speed measured in the film plane in the range of 1.01 to 1.12. An optical compensation sheet characterized by having a ratio of the maximum value to the minimum value. The optical compensation sheet according to claim 1 or 2, wherein the cellulose acylate film is a cellulose acetate film. The optical compensation sheet according to claim 2, wherein the liquid crystal compound is a discotic liquid crystal compound. A polarizing plate comprising a polarizing film and two transparent protective films disposed on both sides thereof, wherein one of the transparent protective films is the optical compensation sheet according to claim 1 or 2. . A liquid crystal display device comprising a liquid crystal cell and two polarizing plates disposed on both sides thereof, wherein the polarizing plate comprises a polarizing film and two transparent protective films disposed on both sides of the liquid crystal cell. 3. A liquid crystal display device, wherein at least one of the transparent protective films is the optical compensation sheet according to claim 1 or 2. The liquid crystal display device according to claim 6, wherein the liquid crystal cell is a TN mode liquid crystal cell. The cellulose acylate solution is cast on a metal substrate, peeled off from the metal substrate, and then dried. In the method for producing a cellulose acylate film, the residual volatile content of the cellulose acylate film after peeling is 45 to 70%. A method for producing a cellulose acylate film comprising drying for 10 to 1000 seconds with warm air of 100 to 160 ° C.