JP3995387B2 - Transparent film for protecting polarizing plate and polarizing plate using the same - Google Patents

Description

ここで、相溶ブレンドであるのでｆＡ ＝ｆＢ と仮定すると、（ｂ）式は以下のように書き表せる。
【００３８】
【数６】

次に表１に記すような仮想的な値を（ｃ）式に用いて、複屈折波長分散値について検討した。なお、表１ではΔｎ０ Ａ (450) 、Δｎ０ Ｂ (450) の代わりに、 高分子Ａ，Ｂ単独の複屈折分散値を記した。
【００３９】
【表１】

【００４０】
式（ｃ）は表１の値が与えられるとφＡの関数としてそれぞれ図２〜５のように表される。ケース１〜４はそれぞれ図２〜５に対応する。表１では正の屈折率異方性を有する高分子を高分子Ａ、負のそれを高分子Ｂとしているので、図２〜５に記した漸近線よりもφＡの少ない領域では、ブレンド高分子の光学異方性は負であり、一方、漸近線よりもφＢの多い領域は異方性は正である。
【００４１】
図２〜５より明らかなように、Δｎ(450) ／Δｎ(550) ＜１となるためには、表１のケース１，３のように、正の高分子の複屈折波長分散係数が負のそれよりも小さくかつ該透明フィルムの光学異方性が正であるか、または、ケース２，４のように高分子単独の複屈折波長分散係数が負のそれよりも大きくかつ該透明フィルムの光学異方性が負である必要がある。ここでは、代表的な波長として450, 550ｎｍを用いたが、他の波長を用いても同様に成立する。
【００４２】
なお、（ｃ）式より考察すると、正と負の高分子の複屈折波長分散係数が完全に等しい場合には、本発明の透明フィルムは得られない。
【００４３】
上記考察は、上記式（ａ）を基にした考察であるが、後述する実施例のように実際の系でもこの考え方は非常によく成り立つので、この考え方が正しいことは実施例でも証明される。例えば、後述する実施例においてフルオレン骨格を有するポリカーボネート共重合体では、Δｎ(450) ／Δｎ(550) ＜１となるときに、異方性は正であるので、厳密には値は異なるが表４のケース１、３に相当し、また、ポリスチレンとポリフェニレンオキサイドのブレンドの場合には、Δｎ(450) ／Δｎ(550) ＜１となるときに、異方性は負であるので、厳密には値は異なるが表４のケース２、４に相当するものと考えられる。
【００４４】
上記の考察は２成分について述べたが、３成分以上でも上記の考え方は成立する。例えば、正の光学異方性を有する成分が２成分と負の異方性を有する成分が１成分である系では、正の光学異方性を有する成分の複屈折率値及び複屈折分散値等を正の異方性の２成分間の体積分率等で補正し、この２成分を１成分と見なして上記式（ａ）以下の考察の考え方を適用することが可能である。
【００４５】
また、上記式（ａ）に基づく説明は高分子Ａ，Ｂのブレンドとして説明したが、高分子が異なるモノマー単位を含む共重合体の場合にも上述した考察の考え方は同様に成立し、第１のモノマー単位に基づく単独重合体（高分子Ａ）と第１のモノマー単位と異なる第２のモノマー単位に基づく単独重合体（高分子Ｂ）とから成ると見なして上記の考え方を適用すればよい。
【００４６】
さらに、単独重合体と共重合体との高分子ブレンドあるいは共重合体どうしの高分子ブレンドでも、上述した考察の考え方を同様に適用することができる。即ち、この場合には、高分子ブレンドの成分高分子を構成するモノマー単位に分けて、その高分子ブレンドをそれぞれのモノマー単位からなる単独重合体の集合体と見なし、この集合体を正の光学異方性を有する単独重合体の群からなる成分Ａと負の異方性を有する単独重合体の群からなる成分Ｂとの組合せと見なして、上記の考察を適用すればよい。
【００４７】
例えば、正の光学異方性を有する高分子Ｘ，Ｙと、負の光学異方性を有するモノマー単位ｘ，ｚの共重合体において、ｘが正の光学異方性を有し、ｚが負の光学異方性を有する場合には、正の光学異方性を有する成分は、Ｘ，Ｙ及びｘからなると考えて、これらの複屈折率値及び複屈折分散値等を正の異方性の３成分間の体積分率等で補正して、これらの３成分を１成分Ａとみなし、負の異方性を有する成分はモノマー単位ｚからなる重合体Ｂと見なして、成分Ａ及び成分Ｂについて、上記（ａ）以下の考察の考え方を適用すればよい。
【００４８】
なお、第１又は第２のモノマー単位に基づく単独高分子において、単独高分子がポリカーボネートの場合、ポリカーボネートは一般にジヒドロキシ化合物とホスゲンとの重縮合により得られるので、重合の観点からは、ビスフェノールからなるジヒドロキシ化合物とホスゲンがモノマーになる。このようにポリカーボネートの場合は、モノマー単位はビスフェノールに由来する部分をいい、ホスゲンに由来する部分は含まない。
【００４９】
一般に室温付近で測定された光学弾性係数と、何らかの高分子成形後、フィルム成形の場合には製膜や延伸工程後に発現する位相差を関連付けて議論することが多いが、実際は必ずしも対応するものではない。むしろ、位相差は複屈折とフィルム膜厚との積であり、また複屈折は固有複屈折と配向関数との積であるので、分子設計の立場からはこの固有複屈折と配向関数について考える必要がある。小さい位相差値を有している透明フィルムを生産性よく得る為には、まず、この固有複屈折を小さくすることが重要である。配向関数は高分子の配向に関する因子であるので、これは成形プロセスに依存すると考えられる。通常フィルムの成形工程として用いられる溶液キャスト製膜工程を考えた場合、固有複屈折が大きいものはプロセスにて配向関数を下げる必要があり、何らかの温度むらや張力むら等の外乱要因があった場合には、これが配向関数の不均一性に繋がり、結果として得られる透明フィルムは位相差の大きいものになる。一方、固有複屈折の小さいものであれば、配向関数に多少むらがあっても、位相差が小さくかつ均一なものが得られると予想される。本発明では固有複屈折が小さい材料を用いている。
【００５０】
【発明の実態の形態】
本発明における偏光板保護用透明フィルムは、吸水率１重量％以下の熱可塑性樹脂からなる１枚の透明フィルムからなり、上記式（１）〜（３）を同時に満足することを特徴としている。なお、上記式（１）について好ましくは｜R(550)｜≦１０ｎｍ、より好ましくは｜R(550)｜≦５ｎｍである。上記式（２）については、好ましくは｜K(550)｜≦２５ｎｍ、より好ましくは｜K(550)｜≦１０ｎｍである。上記式（１）、（２）では位相差を測定波長550ｎｍで定義しているが、可視光波長で測定して上記値を満足することが好ましい。
【００５１】
上記特性を透明フィルム１枚で満足するための材料に対する原理についてはすでに述べたので、以下具体的な材料について説明する。
【００５２】
本発明の偏光板保護用透明フィルムの吸水率は１重量％以下であることが必要である。透明フィルムの吸水率が１重量％を超えると偏光板用保護フィルムとして実用する上で特に高温高湿環境下においては問題が生じる場合がある。特に好ましくは０．５重量％以下の条件を満たすように選択すると、湿熱耐久性がより高まるのでよい。
【００５３】
さらに本発明の偏光板保護用透明フィルムは、ガラス転移点温度が１２０℃以上であることが好ましい。これ未満では、耐久試験時等に収縮等の変形の問題等が発生する場合がある。
【００５４】
本発明の偏光板保護用透明フィルムを構成する熱可塑性樹脂は特に限定されず、上記の条件をかかるフィルム１枚で満たす（共重合）ポリマー、それらのブレンド体であれば特に制限はない。例えば、耐熱性に優れ、光学性能が良好で、溶液製膜ができる材料、例えばポリアリレート、ポリエステル、ポリカーボネート、ポリオレフィン、ポリエーテル、ポリスルフィン系共重合体、ポリスルホン、ポリエーテルスルホンなどの熱可塑性ポリマーが好適である。
【００５５】
この熱可塑性ポリマーを用いた場合、上述したように、正の屈折率異方性を有する高分子と負の屈折率異方性を有する高分子とからなるブレンド高分子、正の屈折率異方性を有する高分子のモノマー単位と負の屈折率異方性を有する高分子のモノマー単位とからなる共重合体がより好適である。それらは２種類以上組合せてもよく、また１種類以上のブレンド高分子と１種類以上の共重合体とを組合せて用いてもよい。
【００５６】
ブレンド高分子であれば、光学的に透明である必要があることから相溶ブレンドまたは、各々の高分子の屈折率が略等しいことが好ましい。ブレンド高分子の具体的な組み合わせとしては、例えば負の光学異方性を有する高分子としてポリ（メチルメタクリレート）と、正の光学異方性を有する高分子としてポリ（ビニリデンフロライド）、ポリ（エチレンオキサイド）及びポリ（ビニリデンフロライド−コ−トリフルオロエチレン）からなる群から選ばれる少なくとも一種のポリマーとの組み合わせ、正の光学異方性を有する高分子としてポリ（フェニレンオキサイド）と、負の光学異方性を有する高分子としてポリスチレン、ポリ（スチレン−コ−ラウロイルマレイミド）、ポリ（スチレン−コ−シクロヘキシルマレイミド）及びポリ（スチレン−コ−フェニルマレイミド）からなる群から選ばれる少なくとも一種のポリマーとの組み合わせ、負の光学異方性を有するポリ（スチレン−コ−マレイン酸無水物）と正の光学異方性を有するポリカーボネートとの組み合わせ、正の光学異方性を有するポリ（アクリロニトリル−コ−ブタジエン）と負の光学異方性を有するポリ（アクリロニトリル−コ−スチレン）との組み合わせ、正の光学異方性を有するポリカーボネートと負の光学異方性を有するポリカーボネートとの組み合わせを好適に挙げることができるが、これらに限定されるものではない。特に透明性の観点から、ポリスチレンと、ポリ（２，６−ジメチル−１，４−フェニレンオキサイド）等のポリ（フェニレンオキサイド）とを組み合わたブレンドポリマー、正の光学異方性を有するポリカーボネートと負の光学異方性を有するポリカーボネートとを組み合わせたブレンド体が好ましい。前者の場合、該ポリスチレンの比率が全体の６７重量％以上７５重量％以下を占めることが好ましい。後者の場合、正の光学異方性を有するビスフェノールＡをジオール成分とするポリカーボネートと、ビスフェノールフルオレンをジオール成分とする、フルオレン骨格を主として有するポリカーボネートとを配合してなるものが好ましい。該ビスフェノールフルオレン成分のブレンド体全体における含有率は、３０〜９０モル％が好適である。
【００５７】
また、共重合体としては例えばポリ（ブタジエン−コ−ポリスチレン）、ポリ（エチレン−コ−ポリスチレン）、ポリ（アクリロニトリル−コ−ブタジエン）、ポリ（アクリロニトリル−コ−ブタジエン−コ−スチレン）、ポリカーボネート共重合体、ポリエステル共重合体、ポリエステルカーボネート共重合体、ポリアリレート共重合体等を用いることが出来る。特に、フルオレン骨格を有するセグメントは負の光学異方性となり得るため、フルオレン骨格を有するポリカーボネート共重合体、ポリエステル共重合体、ポリエステルカーボネート共重合体、ポリアリレート共重合体等はより好ましく用いられる。
【００５８】
上記高分子材料は、２種類以上の共重合体のブレンド体でもよく、１種以上の共重合体と上記ブレンド体または他のポリマーとからなるブレンド体であってもよく、２種類以上のブレンド体または共重合体または他のポリマーのブレンド体でもよい。これらの場合、該ビスフェノールフルオレン成分の全体における含有率は、３０〜９０モル％とすることが好適である。
【００５９】
ビスフェノール類とホスゲンあるいは炭酸ジフェニルなどの炭酸エステル形成性化合物と反応させて製造されるポリカーボネート共重合体は透明性、耐熱性、生産性に優れており特に好ましく用いることが出来る。ポリカーボネート共重合体としては、フルオレン骨格を有する構造を含む共重合体であることが好ましい。フルオレン骨格を有する成分は式（Ｉ）で表わされる繰返し単位であり、繰返し単位全体の１〜９９モル％含まれていることが好ましい。
【００６０】
具体的には、下記式（Ｉ）
【００６１】
【化８】

【００６２】
（上記式（I）において、Ｒ₁〜Ｒ₈はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜６の炭化水素基から選ばれる少なくとも一種であり、Ｘは
【００６３】
【化９】

【００６４】
である。）
で示される繰り返し単位を３０〜９０モル％と、下記式（II）
【００６５】
【化１０】

【００６６】
（上記式（II）において、Ｒ₉〜Ｒ₁₆はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜２２の炭化水素基から選ばれる少なくとも一種であり、Ｙは下記式群
【００６７】
【化１１】

【００６８】
（ここで、Ｙ中のＲ₁₇〜Ｒ₁₉、Ｒ₂₁及びＲ₂₂はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜２２の炭化水素基から、Ｒ₂₀及びＲ₂₃はそれぞれ独立に炭素数１〜２０の炭化水素基から選ばれ、Ａｒは炭素数６〜１０のアリール基から選ばれる少なくとも一種の基である。）
で示される繰り返し単位が全体の７０〜１０モル％を占めるポリカーボネート共重合体が挙げられる。
【００６９】
上記式（I）において、Ｒ₁〜Ｒ₈はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜６の炭化水素基から選ばれる。かかる炭素数１〜６の炭化水素基としては、メチル基、エチル基、イソプロピル基、シクロヘキシル基等のアルキル基、フェニル基等のアリール基が挙げられる。この中で、水素原子、メチル基が好ましい。
【００７０】
上記式（II）において、Ｒ₉〜Ｒ₁₆はそれぞれ独立に水素原子、ハロン原子及び炭素数１〜２２の炭化水素基から選ばれる。かかる炭素数１〜２２の炭化水素基としては、メチル基、エチル基、イソプロピル基、シクロヘキシル基等の炭素数１〜９のアルキル基、フェニル基、ビフェニル基、ターフェニル基等のアリール基が挙げられる。この中で、水素原子、メチル基が好ましい。
【００７１】
上記式（II）のＹにおいて、Ｒ₁₇〜Ｒ₁₉、Ｒ₂₁及びＲ₂₂はそれぞれ独立に水素原子、ハロゲン原子及び炭素数１〜２２の炭化水素基から選ばれる少なくとも一種の基である。かかる炭化水素基については、上記したものと同じものを挙げることができる。Ｒ₂₀及びＲ₂₃はそれぞれ独立に炭素数１〜２０の炭化水素基から選ばれ、かかる炭化水素基については、上記したものと同じものを挙げることができる。Ａｒはフェニル基、ナフチル基等の炭素数６〜１０のアリール基である。
【００７２】
本発明における透明フィルムは、フルオレン骨格を有するポリカーボネートを用いたものが好ましい。このフルオレン骨格を有するポリカーボネートとしては、例えば上記式（Ｉ）で表わされる繰り返し単位と上記式（II）で表わされる繰り返し単位とからなるポリカーボネート共重合体、上記式（I）で表わされる繰り返し単位からなるポリカーボネートと上記式（II）で表わされる繰り返し単位からなるポリカーボネートとのブレンド体がよく、上記式（I）の含有率、すなわち共重合体の場合共重合組成、ブレンド体の場合ブレンド組成比は、ポリカーボネート全体の３０〜９０モル％が好適である。かかる範囲を外れた場合には、小さい位相差値を有する位相差フィルムを均一に得ることが困難となる。上記式（Ｉ）の含有率は、ポリカーボネート全体の３５〜８５モル％が好ましく、５0〜８０モル％がより好ましい。
【００７３】
上記共重合体は、上記式（I）および（II）で表わされる繰り返し単位をそれぞれ２種類以上組み合わせたものでもよく、ブレンド体の場合も、上記繰り返し単位はそれぞれ２種類以上組み合わせてもよい。
【００７４】
ここで上記モル比は共重合体、ブレンド体に関わらず、透明フィルムを構成するポリカーボネートバルク全体で、例えば核磁気共鳴(NMR）装置により求めることができる。
【００７５】
上記フルオレン骨格を有するポリカーボネートとしては、下記式（III）
【００７６】
【化１２】

【００７７】
（上記式（III）において、Ｒ₂₄及びＲ₂₅はそれぞれ独立に水素原子およびメチル基から選ばれる少なくとも一種である。）
で示される繰り返し単位を３５〜８５モル％と、下記式（IV）
【００７８】
【化１３】

【００７９】
（上記式（IV）において、Ｒ₂₆及びＲ₂₇はそれぞれ独立に水素原子、メチル基から選ばれ、Ｚは下記式群
【００８０】
【化１４】

【００８１】
から選ばれる少なくとも一種の基である。）
が全体の６５〜１５モル％を占めるポリカーボネート共重合体及び/またはブレンド体を用いることが特に好ましい。
【００８２】
上記した共重合体及び／またはブレンド体は公知の方法によって製造し得る。ポリカーボネートはジヒドロキシ化合物とホスゲンとの重縮合による方法、溶融重縮合法等が好適に用いられる。ブレンド体の場合は、相溶性ブレンドが好ましいが、完全に相溶しなくても成分間の屈折率を合わせれば成分間の光散乱を抑え、透明性を向上させることが可能である。
【００８３】
上記ポリカーボネートの極限粘度は０．３〜２．０ｄl／ｇであることが好ましい。０．３未満では脆くなり機械的強度が保てないといった問題があり、３．０を超えると溶液粘度が上がりすぎるため溶液製膜においてダイラインの発生等の問題や、重合終了時の精製が困難になるといった問題がある。
【００８４】
本発明の偏光板保護用透明フィルムは透明性が高いことが必要で、具体的にはヘーズ値は３％以下、全光線透過率は測定波長３８０〜７８０ｎｍにおいて８０％以上、好ましくは８５％以上であることが好ましい。さらに無色透明であることが好ましいが、JISZ-8279に記載のＬ^*ａ^*ｂ^*表色系のうち、２度視野C光源を用いたｂ^*で定義するなら、１．３以下であることが好ましく、より好ましくは０．９以下である。
【００８５】
本発明の偏光板保護用透明フィルムは、さらに、フェニルサリチル酸、２−ヒドロキシベンゾフェノン、トリフェニルフォスフェート等の紫外線吸収剤や、色味を変えるためのブルーイング剤、酸化防止剤等を含有してもよい。
【００８６】
本発明の偏光板保護用透明フィルムの製造方法としては、公知の溶融押し出し法、溶液キャスト法等が用いられるが、膜厚むら、外観等の観点から溶液キャスト法がより好ましく用いられる。溶液キャスト法における溶剤としては、メチレンクロライド、ジオキソラン等が好適が用いられる。残留メチクロ量としては０．５重量％以下が好ましく、より好ましくは０．３重量％以下、さらに好ましくは０．１重量％以下である。
【００８７】
かくして得られた透明フィルムは、必要に応じて、所望の光学特性となるように、延伸等を行い高分子鎖を配向させてもよい。延伸方法としては、公知の延伸方法を使用し得るが、好ましくは縦一軸延伸である。この際、かかるフィルム中には延伸性を向上させる目的で、可塑剤を添加することができる。可塑剤等の添加剤は、位相差波長分散を変化させ得るが、添加量は、ポリマー固形分対比１０wt％以下が好ましく、３wt％以下がより好ましい。
【００８８】
本発明の偏光板保護用透明フィルムの膜厚としては、５μｍから ２００μｍであることが好ましく、より好ましくは１０〜１２０μｍである。
【００８９】
光学異方性を持った透明なフィルムには一般に斜めからの入射光に対しては、正面入射光と比較して異なる位相差値を与えることが知られている。ここで高分子材料の三次元屈折率とは、ｎｘ，ｎｙ，ｎｚで表され、それぞれの定義は、
ｎｘ：透明フィルム面内における主配向方向の屈折率
ｎｙ：透明フィルム面内における主配向方向に直交する方位の屈折率
ｎｚ：透明フィルム表面の法線方向の屈折率
とする。ここで、主配向方向とは例えばフィルムの流れ方向を意味しており、化学構造的には高分子主鎖の配向方向を指す。nx>nzのときを光学異方性が正、nx<nzのときを光学異方性が負であるとここでは呼ぶ。この三次元屈折率は、透明フィルムに偏光を入射して得られる出射光の偏光状態を解析する手法である偏光解析法により測定されるが、本発明では透明フィルムの光学異方性を屈折率楕円体と見なして公知の屈折率楕円体の式により求める方法によりこの三次元屈折率を求めている。この三次元屈折率は使用する光源の波長依存性があるので、使用する光源波長で定義することが好ましい。この三次元屈折率を用いて光学異方性を表記する方法として下記式（８）
【００９０】
【数７】
Ｎｚ＝（ｎｘ−ｎｚ）／（ｎｘ−ｎｙ） （８）
があるが、これを用いて三次元屈折率を定義するならば、 Nzが０．３〜１．５の範囲にあるとき、非常に位相差値の入射角依存性が小さくなる。特にNz=0.5のときは位相差値の入射角依存性が実質的に無くなり、どの角度から光が入っても同じ位相差値を与える。
【００９１】
なお、上記定義によれば、正の光学異方性を有する透明フィルムの遅相軸はnx,進相軸はnyとなる。
【００９２】
本発明の偏光板保護用透明フィルムとして用いられる透明フィルムの位相差を短波長ほど小さくするためには、先述の通り特定の化学構造を有することが必須条件であり、位相差波長分散はかなりの部分がその化学構造で決まるが、添加剤、製膜条件、ブレンド状態、分子量等によっても変動することに留意されるべきである。
【００９３】
本発明の偏光板保護用透明フィルムを用いてなる偏光板の構成としては、該透明フィルムが偏光層の両側または片側に設置されているもので、偏光層と透明フィルム間の接着は接着剤または粘着剤が用いられる。該透明フィルムが偏光層の両側に設置されてなる偏光板の概略断面図を図１に記す。この接着を良好なものするために、透明フィルム上にコーテイング層やコロナ処理、親水処理等を行なっても良い。また、本発明の偏光板保護用透明フィルムが例えば、表示装置の最表面に設置される場合には、ハードコート層、反射防止層、防眩処理等を行なっても良い。偏光層とは、この場合無偏光から偏光を発生させる層をいい、例えば、ポリビニルアルコール等高分子にヨウ素や二色性色素を分散配向させたもの、二色性を有する高分子、ポリアセチレンを配向させたもの等を指す。
【００９４】
【発明の効果】
以上説明したように、本発明により吸水率１重量％以下の熱可塑性樹脂からなる透明フィルム１枚で光学異方性が小さくかつ位相差が短波長ほど小さい偏光板保護用透明フィルムを量産性良く提供することが出来るので、これを偏光板に用いることにより例えば耐久性と偏光性能に優れた偏光板が実現できる。
【００９５】
【実施例】
以下に実施例を挙げて本発明をより詳細に説明するが、本発明はこれらに限定されるものではない。
（評価法）
本明細書中に記載の材料特性値等は以下の評価法によって得られたものである。
（１）位相差値（R＝Δn・d(nm)）、K値の測定
偏光板用保護フィルムの複屈折Δnと膜厚ｄの積である位相差R値及びK値は、分光エリプソメータである日本分光（株）製の商品名『Ｍ１５０』により測定した。R値は入射光線とフィルム表面が直交する状態で測定した。また、K値(nm)は入射光線とフィルム表面の角度を変えることにより、各角度での位相差値を測定し、公知の屈折率楕円体の式でカーブフィッチングすることにより三次元屈折率であるnx,ny,nzを求め、下記式（７）に代入することにより求めた。
【００９６】
【数８】
Ｋ＝（ｎｚ−（ｎｘ＋ｎｙ）／２）＊ｄ （７）
【００９７】
（２）吸水率の測定
乾燥させたフィルムの状態で膜厚を 130±50μｍとした以外は、JIS K 7209記載の『プラスチックの吸水率及び沸騰吸水率試験方法』に準拠して測定した。試験片の大きさは50mm正方形で、水温25℃、24時間サンプルを浸水させた後、重量変化を測定した。いわゆる飽和吸水量であり単位は重量％である。
【００９８】
（３）高分子のガラス転移点温度（Tg）の測定
TA Instruments社製『DSC2920 Modulated DSC 』により測定した。フィルム成形後ではなく、樹脂重合後、フレークスまたはチップの状態で測定した。
【００９９】
（４）フィルム膜厚測定
アンリツ社製の電子マイクロで測定した。
【０１００】
（５）高分子共重合比の測定
日本電子社製『JNM-alpha600』のプロトンNMRにより測定した。特にビスフェノールＡとビスクレゾールフルオレンの共重合体の場合には、溶媒として重ベンゼンを用い、それぞれのメチル基のプロトン強度比から算出した。
【０１０１】
（６）透過率の測定
日立製作所製の分光光度計である商品名『U-3500』を用いた。測定波長は３８０〜７８０ｎｍとしたが、実施例では測定波長５５０ｎｍに代表させて記載している。
【０１０２】
また、以下の実施例、比較例で用いたポリカーボネートのモノマー構造を以下に記す。
【０１０３】
【化１５】

【０１０４】
［実施例１］
攪拌機、温度計及び還流冷却器を備えた反応槽に水酸化ナトリウム水溶液及びイオン交換水を仕込み、これに上記構造を有するモノマー[A]と[F]を表２のモル比で溶解させ、少量のハイドロサルファイトを加えた。次にこれに塩化メチレンを加え、２０℃でホスゲンを約６０分かけて吹き込んだ。さらに、p-tert-ブチルフェノールを加えて乳化させた後、トリエチルアミンを加えて３０℃で約３時間攪拌して反応を終了させた。反応終了後有機相分取し、塩化メチレンを蒸発させてポリカーボネート共重合体を得た。得られた共重合体の組成比はモノマー仕込み量比とほぼ同様であった。
【０１０５】
この共重合体をメチレンクロライドに溶解させ、固形分濃度２０重量％のドープ溶液を作製した。このドープ溶液からキャストフィルムを作製し透明フィルムを得た。
【０１０６】
表２に測定結果をまとめる。このフィルムは、R、K値ともに小さく、また、１ｍ幅のフィルムで幅方向を測定してR（５５０）のばらつきの範囲は±０．５ｎｍであった。測定波長４００〜７００ｎｍにおいて短波長ほど位相差が小さくなり、かつ、屈折率異方性は正であることを確認した。偏光板保護用フィルムとして好適であることが分かった。
【０１０７】
［実施例２］
表２記載のモノマーを使った以外は実施例１と同様の方法にてポリカーボネート共重合体を得た。得られた共重合体の組成比はモノマー仕込み量比とほぼ同様であった。実施例１と同様に製膜し透明フィルムを得た。表２に測定結果をまとめる。また測定波長４００〜７００ｎｍにおいて短波長ほど位相差が小さくなりかつ、屈折率異方性は正であることを確認した。
【０１０８】
［実施例３］
表２記載のモノマーを使った以外は実施例１と同様の方法にてポリカーボネート共重合体を得た。得られた共重合体の組成比はモノマー仕込み量比とほぼ同様であった。実施例１と同様に製膜し透明フィルムを得た。表２に測定結果をまとめる。また測定波長４００〜７００ｎｍにおいて短波長ほど位相差が小さくなりかつ、屈折率異方性は正であることを確認した。
【０１０９】
［実施例４］
表２記載のモノマーを使った以外は実施例１と同様の方法にてポリカーボネート共重合体を得た。得られた共重合体の組成比はモノマー仕込み量比とほぼ同様であった。実施例１と同様に製膜し透明フィルムを得た。表２に測定結果をまとめる。また測定波長４００〜７００ｎｍにおいて短波長ほど位相差が小さくなりかつ、屈折率異方性は正であることを確認した。
【０１１０】
［実施例５］
表２記載のモノマーを使った以外は実施例１と同様の方法にてポリカーボネート共重合体を得た。得られた共重合体の組成比はモノマー仕込み量比とほぼ同様であった。実施例１と同様に製膜し透明フィルムを得た。表２に測定結果をまとめる。また測定波長４００〜７００ｎｍにおいて短波長ほど位相差が小さくなりかつ、屈折率異方性は正であることを確認した。
【０１１１】
［実施例６］
表２記載のモノマーを使った以外は実施例１と同様の方法にてポリカーボネート共重合体を得た。得られた共重合体の組成比はモノマー仕込み量比とほぼ同様であった。実施例１と同様に製膜し透明フィルムを得た。表２に測定結果をまとめる。また測定波長４００〜７００ｎｍにおいて短波長ほど位相差が小さくなりかつ、屈折率異方性は正であることを確認した。
【０１１２】
［実施例７］
負の屈折率異方性を有する高分子としてポリスチレン（和光純薬工業（株））、正の屈折率異方性を有する高分子としてポリフェニレンオキサイド（ポリ（２，６−ジメチル １，４−フェニレンオキサイド）和光純薬工業（株））を、それぞれ70, 30重量％の比率でクロロホルムに溶解させ、固形分濃度18重量％のドープ溶液を作製した。このドープ溶液からキャストフィルムを作製し透明フィルムを得た。
【０１１３】
表２に光学特性測定結果をまとめる。このフィルムは、測定波長４００〜７００ｎｍにおいて短波長ほど位相差が小さくなりかつ、屈折率異方性は負であることを確認した。偏光板保護用透明フィルムとして好適であることが分かった。
【０１１４】
参考として、ポリスチレン、ポリフェニレンオキサイドのブレンド比率を変えた際の複屈折波長分散係数とポリフェニレンオキサイドの体積分率との関係を図６に記す。ポリフェニレンオキサイドの少ない領域では、光学異方性は負であり、複屈折波長分散係数が１より小さくなる領域が存在することが分かる。一方、ポリフェニレンオキサイドの多い屈折率異方性が正の領域ではその値は１より大きい。
【０１１５】
次に、前述の式（ｃ）を用いて計算した図６のような体積分率と複屈折波長分散係数との関係を図７に記す。図７はポリスチレン、ポリフェニレンオキサイドの波長 550ｎｍにおける固有複屈折をそれぞれ、−0.10, 0.21 (D. Lefebvre, B. Jasse and L. Monnerie, Polymer 23 706-709 (1982)を参考）、また、それぞれのR(450)/R(550)の値を、１．０６，１．１５として計算した。図６と図７の一致は良いといえる。ポリスチレン、ポリフェニレンオキサイドの密度はそれぞれ、1.047, 1.060ｇ／cm³とした。
【０１１６】
【表２】

【０１１７】
［比較例１］
市販のビスフェノールＡとホスゲンとの重縮合からなる市販のポリカーボネート（帝人化成製『パンライトC1400』）を用いて、実施例１と同様に製膜し透明フィルムを得た。表３に測定結果をまとめる。Ｋ値が負に大きく、また、測定波長が短波長ほど位相差が大きく、本発明で目的としているところの偏光板保護用フィルムとしては好ましくないことが分かった。
【０１１８】
［比較例２］
市販のノルボルネン樹脂であるJSR製の『ARTON』を用いて、実施例１と同様に製膜した。表３に測定結果をまとめる。K値が負に大きく、また、測定波長が短波長ほど位相差が大きく、本発明で目的としているところの偏光板保護用フィルムとしては好ましくないことが分かった。
【０１１９】
［比較例３］
トリアセチルセルロース樹脂（和光純薬工業（株）、極限粘度[η]１．３３５、アセチル化度２．９１７）を用いて、溶媒を塩化メチレン/メタノール（重量比９／１）とした以外は実施例１と同様に製膜した。表３に測定結果をまとめる。Ｋ値が正に大きく、また、測定波長が短波長ほど絶対値で位相差が大きく、また、吸水率は４重量％であり、本発明で目的としているところの偏光板保護用フィルムとしては好ましくないことが分かった。
【０１２０】
【表３】

【図面の簡単な説明】
【図１】本発明の偏光板保護用透明フィルムを用いた偏光板の一例の概略断面図である。
【図２】表１のケース１に対応する二成分ブレンド高分子の複屈折の波長分散と体積分率φAの関係を示すグラフである。
【図３】表１のケース２に対応する二成分ブレンド高分子の複屈折の波長分散と体積分率φAの関係を示すグラフである。
【図４】表１のケース３に対応する二成分ブレンド高分子の複屈折の波長分散と体積分率φAの関係を示すグラフである。
【図５】表１のケース４に対応する二成分ブレンド高分子の複屈折の波長分散と体積分率φAの関係を示すグラフである。
【図６】ポリスチレンとポリフェニレンオキサイドのブレンドにおけるポリフェニレンオキサイドの体積分率とR(450)/R(550)の関係を示すグラフである。（実測値）
【図７】ポリスチレンとポリフェニレンオキサイドのブレンドにおけるポリフェニレンオキサイドの体積分率とR(450)/R(550)の関係を示すグラフである。（計算値）
【符号の説明】
１：本発明の偏光板保護用透明フィルム
２：接着層
３：偏光層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transparent film for protecting a polarizing plate used for a polarizing plate and a polarizing plate using the same.
[0002]
[Prior art]
The polarizing plate is used in sunglasses, antireflection films, liquid crystal display devices and the like, and is mainly used as an optical element that extracts polarized light from non-polarized light. In particular, as a member that expresses the polarizing function of a polarizing plate used in a liquid crystal display device, iodine or a dichroic dye is oriented and held in stretched polyvinyl alcohol, or linear such as polyacetylene. An oriented polymer in which a large number of conjugated double bonds are arranged in the main chain or side chain is used. In general, these polarizing members may have practical problems in terms of scratch resistance, mechanical strength, durability, etc., so a protective film is interposed on one or both sides of the adhesive or adhesive. It is usually installed.
[0003]
As a protective film for polarizing plates widely used in liquid crystal display devices, there is a triacetyl cellulose film.
[0004]
[Problems to be solved by the invention]
Properties required for a protective film for a polarizing plate used in a liquid crystal display device include wet heat durability, transparency, low optical anisotropy, and the like. Good wet heat durability is an essential item especially for a polarizing plate used in a liquid crystal display device used in an automobile, and specifically, a high glass transition temperature and a low water absorption are preferred. In particular, a polarizing plate for a liquid crystal display device used in an automobile is required to have environmental resistance at 100 ° C. or higher. Therefore, it is necessary that the glass transition temperature is high, and at the same time, the water absorption is high. Due to the molecular motion of water in the molecule, deformation such as shrinkage and swelling may occur even at a temperature below the glass transition temperature, and a lower water absorption rate is preferred.
[0005]
Moreover, it is preferable that the protective film of the polarizing plate used for a liquid crystal display device is excellent in transparency, and has small optical anisotropy, and in particular, small three-dimensional refractive index anisotropy. In particular, recent liquid crystal display devices have improved viewing angle characteristics, and the viewing angle characteristics of polarizing plates that are not accompanied by the viewing angle characteristics can be problematic.
[0006]
In particular, a triacetyl cellulose film widely used as a protective film for a polarizing plate for a liquid crystal display device has a high water absorption rate of 4% by weight or more, and problems such as deformation may occur under high temperature and high humidity. In addition, the film can have transparency and in-plane retardation (R (550)) of 10 nm or less, and has excellent properties with small optical anisotropy in two dimensions, but is viewed in three dimensions. Optical anisotropy is large.
[0007]
In contrast to the triacetyl cellulose film having such a problem, a film using another resin has been proposed, but a transparent film made of a thermoplastic resin that has been generally studied has R (550) of, for example, absolute Although a value of 10 nm or less can be realized, the three-dimensional refractive index anisotropy is generally large, and it is particularly difficult to increase productivity. For example, in a case where a polycarbonate having a unit obtained by polycondensation of commercially available bisphenol A is formed into a film by a solution cast film forming method or a melt extrusion method, R (550) can be made to be 10 nm or less. The direction is very large. Even if you try to reduce the three-dimensional refractive index anisotropy forcibly, there are problems such as unevenness in the film plane and extreme deterioration of productivity, which can be obtained in practice, It was very difficult to obtain a transparent film having a small refractive index anisotropy.
[0008]
The large three-dimensional refractive index anisotropy is usually because the refractive index in the film thickness direction is greatly different from the refractive index in the in-plane direction. In the case of solution cast film formation, it is mainly necessary to apply tension to the film in order to eliminate wrinkles of the film in the flow orientation immediately after casting and the subsequent drying process. It seems to be the cause. However, there is a limit to reducing optical anisotropy by improving these film forming processes, and other characteristics such as surface flatness, film thickness unevenness, optical unevenness, etc. are difficult to be compatible. Problems such as extremely low productivity occur.
[0009]
The optical anisotropy described above is expressed by a phase difference (nm), but this phase difference can generally be expressed by an angle. At this time, the conversion formula between the phase difference R1 expressed in angle and the phase difference R2 in the unit of nm is expressed as R1 (degree) = (R2 (nm) / λ) × 360 (λ is a phase difference measurement wavelength) ). The magnitude of the retardation R1 possessed by the protective film for the polarizing plate affects the degree of polarization of the polarizing plate, that is, the image quality such as the contrast of the liquid crystal display device when used in a liquid crystal display device. That is, even when the retardation measurement wavelength used by R2 is always a constant value, R1 increases as the wavelength becomes shorter, and the retardation of the protective film increases as the wavelength becomes shorter. Deteriorates the polarization degree of the polarizing plate. That is, the phase difference represented by R2 is preferably smaller as the wavelength is shorter. For example, if the influence of the retardation of the protective film on the polarization degree of the polarizing plate is to be the same in the visible light range, it is preferable that the change of R2 with respect to wavelength λ approaches the change of wavelength λ. It will be said. This means that the phase difference represented by R2 is preferably smaller as the wavelength is shorter. However, any transparent film made of a normal polymer material usually becomes large when R2 has a short wavelength or is constant at best, so that it is excellent in heat resistance and water resistance, and can withstand practical use. There was no film with such properties. Unless otherwise specified, the phase difference in this specification refers to the unit of nm.
[0010]
  The present invention solves the above problems and reduces in-plane and three-dimensional optical anisotropy.The smaller the wavelength, the smaller the phase differenceAnd it aims at providing the protective film for polarizing plates excellent in wet heat durability.
[0011]
[Means for Solving the Problems]
The present inventors considered that the structure of the polymer is very important for fundamentally reducing the three-dimensional refractive index anisotropy of the protective film.
[0012]
  And in order to solve the said subject, paying attention to the polymer structure etc. of the protective film for polarizing plates, especially a transparent film suitable as a protective film of the polarizing plate of a display apparatus regardless of light emission and non-light emissionInAs a result of intensive studies, a thermoplastic resin capable of giving a transparent film excellent in productivity, optical uniformity, flatness, etc. is selected, and is a single transparent film having a water absorption of 1% by weight or less. The present invention has been achieved by finding a transparent film having extremely high isotropic properties and in-plane and three-dimensional refractive index anisotropy of a specific value or less.
[0013]
  That is, the present invention is a single transparent film made of a thermoplastic resin and having a water absorption of 1% by weight or less,The transparent film has the following condition A or B:
[Condition A]
(I) Polymer monomer unit having positive refractive index anisotropy (hereinafter referred to as first monomer unit) and polymer monomer unit having negative refractive index anisotropy (hereinafter referred to as second monomer) A film composed of a polymer including:
( ii ) R (450) / R (550) of the polymer based on the first monomer unit is smaller than R (450) / R (550) of the polymer based on the second monomer unit, and
( iii ) Having positive refractive index anisotropy,
[Condition B]
(I) A monomer unit that forms a polymer having positive refractive index anisotropy (hereinafter referred to as a first monomer unit) and a monomer unit that forms a polymer having negative refractive index anisotropy (hereinafter referred to as “first monomer unit”). A second monomer unit)) and a polymer composed of a polymer.
( ii ) R (450) / R (550) of the polymer based on the first monomer unit is greater than R (450) / R (550) of the polymer based on the second monomer unit, and
( iii ) Has negative refractive index anisotropy,
A transparent film satisfying any one ofA transparent film for protecting a polarizing plate, characterized in that a retardation at wavelengths of 450 nm and 550 nm simultaneously satisfies the following formulas (1) to (3):Is.
[0014]
[Expression 2]
| R (550) | ≦ 15 nm (1)
| K (550) | ≦ 35 nm (2)
R (450) / R (550) <1 (3)
(Where R (450) and R (550) are in-plane retardations of the transparent film at wavelengths of 450 nm and 550 nm, respectively, and K (550) is K = [nz− (nx + ny) / 2] × d (where nx, ny, and nz are the three-dimensional refractive indexes of the transparent film, which are the refractive indexes in the x-axis, y-axis, and z-axis directions, respectively, and d is the thickness of the film). Value.)
[0015]
In the present invention, the optical anisotropy of the polarizing plate protective transparent film is to satisfy the above (1) and (2), and the retardation of the polarizing plate protective film is smaller as the wavelength is shorter. "Naru" means that the above (3) is satisfied.
[0016]
It is preferable that the retardation of the transparent film is smaller as the wavelength is shorter at a measurement wavelength of 400 to 700 nm. Further, from a practical viewpoint, the retardation of the transparent film at wavelengths of 450 nm, 550 nm, and 650 nm is expressed by the following formula (4) and (5):
[0017]
[Equation 3]
0 <R (450) / R (550) <0.95 (4)
1.02 <R (650) / R (550)> 1.5 (5)
[Wherein, R (650) is the in-plane retardation of the transparent film at a wavelength of 650 nm. ]
It is preferable to satisfy.
[0018]
Here, in the present invention, the retardation and K value of the transparent film at wavelengths of 450, 550, and 650 nm are R (450), R (550), R (650), and K (450), K (550), respectively. , K (650).
[0019]
The retardation of a transparent film (retardation) refers to the phase difference based on the difference in the traveling speed (refractive index) of light in the direction perpendicular to the film orientation direction when light passes through a film of thickness d. It is known that this is expressed by the product Δn · d of the difference Δn in refractive index between the orientation direction and the direction perpendicular thereto and the thickness d of the film.
[0020]
Since the phase difference Δn · d is proportional to the birefringence Δn if the transparent film is the same, the wavelength dispersion (wavelength dependence) of the phase difference can be expressed by the wavelength dispersion (wavelength dependence) of the birefringence Δn.
[0021]
The case where the refractive index in the orientation direction in the plane of the transparent film is larger than the refractive index in the direction perpendicular thereto is referred to as positive optical anisotropy, and the opposite case is referred to as negative optical anisotropy. Here, the orientation direction of the transparent film is, for example, when the film is uniaxially stretched under the condition of the glass transition temperature Tg (Tg ± 20 ° C.) which is a known retardation film production condition. In the case of biaxial stretching, it refers to the direction of stretching so as to increase the orientation.
[0022]
In the present invention, the term “phase difference” means the absolute value of the phase difference. When the optical anisotropy is negative, the phase difference is negative, but in the present invention, the sign of positive and negative is ignored unless otherwise stated.
[0023]
In addition, the measurement optical wavelength used to determine whether the optical anisotropy is positive or negative is 550 nm.
[0024]
According to the present invention, it has been found that a transparent film having a smaller optical anisotropy and a smaller retardation as a wavelength can be obtained by a transparent film that satisfies the following condition (A) or (B).
[0025]
(A) (i) Polymer monomer unit having positive refractive index anisotropy (hereinafter referred to as first monomer unit) and polymer monomer unit having negative refractive index anisotropy (hereinafter referred to as second monomer unit) )) Comprising a polymer,
(ii) R (450) / R (550) of the polymer based on the first monomer unit is smaller than R (450) / R (550) of the polymer based on the second monomer unit, and
(iii) Having positive refractive index anisotropy,
Transparent film.
[0026]
(B) (i) A monomer unit forming a polymer having positive refractive index anisotropy (hereinafter referred to as a first monomer unit) and a monomer unit forming a polymer having negative refractive index anisotropy (hereinafter referred to as a second monomer unit). Comprising a polymer containing a monomer unit of
(ii) R (450) / R (550) of the polymer based on the first monomer unit is greater than R (450) / R (550) of the polymer based on the second monomer unit, and
(iii) Has negative refractive index anisotropy,
Transparent film.
[0027]
  Above (A)OrAs an example of an embodiment that satisfies the condition (B), there is one that satisfies the following conditions (C) and (D).
[0028]
(C) (i) Blend polymer composed of a polymer having a positive refractive index anisotropy and a polymer having a negative refractive index anisotropy and / or a monomer unit of a polymer having a positive refractive index anisotropy and a negative A film composed of a copolymer composed of polymer monomer units having refractive index anisotropy,
(ii) R (450) / R (550) of the polymer having positive refractive index anisotropy is smaller than R (450) / R (550) of the polymer having negative refractive index anisotropy, And
(iii) Having positive refractive index anisotropy,
Transparent film.
[0029]
(D) (i) Blend polymer composed of a polymer having a positive refractive index anisotropy and a polymer having a negative refractive index anisotropy and / or a monomer unit of a polymer having a positive refractive index anisotropy and a negative A film composed of a copolymer composed of polymer monomer units having refractive index anisotropy,
(ii) R (450) / R (550) of the polymer having positive refractive index anisotropy is larger than R (450) / R (550) of the polymer having negative refractive index anisotropy, And
(iii) Has negative refractive index anisotropy,
Transparent film.
[0030]
Here, the polymer having positive or negative refractive index anisotropy refers to a polymer that gives a transparent film having positive or negative refractive index anisotropy.
[0031]
The reason why this transparent film is a necessary condition that the retardation becomes smaller as the measurement wavelength is shorter will be described below.
[0032]
In general, it is known that the birefringence Δn of a polymer blend composed of two components of polymer A and polymer B is expressed as follows. (H. Saito and T. Inoue, J. Pol. Sci. Part B, 25, 1629 (1987))
[0033]
[Expression 4]
Δn = Δn0 A fA φA + Δn0 B fB φB + ΔnF (a)
Where Δn0 A is the intrinsic birefringence of polymer A, Δn0 B is the intrinsic birefringence of polymer B, fA is the orientation function of polymer A, fB is the orientation function of polymer B, and φA is the volume of polymer A. Fraction, φB: volume fraction of polymer B (= 1−φA), ΔnF: structural birefringence. In general, the birefringence Δn is represented by Δn = fΔn0. Δn0 can be obtained by combining dichroic infrared spectroscopy and phase difference measurement.
[0034]
In the equation (a), the change in polarizability due to the electronic interaction between the polymers A and B is completely ignored, but this assumption is also adopted below. Further, in the retardation film application as in the present invention, since it is required to be optically transparent, the blend is preferably a compatible blend. In this case, ΔnF is very small and ignored. I can do it.
[0035]
Next, regarding a transparent film in which birefringence decreases as the measurement wavelength becomes shorter, only 450 and 550 nm are considered here as the measurement wavelength. If the birefringence of the retardation film at these wavelengths is Δn (450) and Δn (550), respectively, it can be expressed as Δn (450) / Δn (550) <1. Needless to say, a retardation film made of a normal polymer film satisfies Δn (450) / Δn (550)> 1, for example, Δn (450) / Δn (550) of a polycarbonate obtained by polymerization of bisphenol A and phosgene. Is about 1.08, and it is about 1.01 even for polyvinyl alcohol, which is said to have low birefringence wavelength dispersion.
[0036]
When Δn (450) / Δn (550) is a birefringence wavelength dispersion coefficient, it is expressed as follows using equation (a).
[0037]
[Equation 5]

Here, since it is a compatible blend, assuming fA = fB, equation (b) can be written as follows.
[0038]
[Formula 6]

Next, hypothetical values as shown in Table 1 were used in the equation (c) to examine the birefringence wavelength dispersion value. In Table 1, instead of Δn0 A (450) and Δn0 B (450), the birefringence dispersion values of the polymers A and B alone are shown.
[0039]
[Table 1]

[0040]
The expression (c) is expressed as a function of φA as shown in FIGS. Cases 1 to 4 correspond to FIGS. In Table 1, since the polymer having positive refractive index anisotropy is polymer A and the polymer having negative refractive index is polymer B, in the region where φA is smaller than the asymptote shown in FIGS. The optical anisotropy is negative, while the region with more φB than the asymptote has positive anisotropy.
[0041]
As is apparent from FIGS. 2 to 5, in order to satisfy Δn (450) / Δn (550) <1, the birefringence wavelength dispersion coefficient of the positive polymer is negative as in cases 1 and 3 of Table 1. And the transparent film has a positive optical anisotropy, or the birefringence wavelength dispersion coefficient of the polymer alone is larger than that of the negative film as in cases 2 and 4, and the transparent film The optical anisotropy needs to be negative. Here, 450 and 550 nm are used as typical wavelengths, but the same holds true when other wavelengths are used.
[0042]
In consideration of the formula (c), when the birefringence wavelength dispersion coefficients of the positive and negative polymers are completely equal, the transparent film of the present invention cannot be obtained.
[0043]
The above consideration is based on the above formula (a), but this idea is very well established in an actual system as in the example described later, and it is proved in the example that this idea is correct. . For example, in the polycarbonate copolymer having a fluorene skeleton in the examples described later, the anisotropy is positive when Δn (450) / Δn (550) <1, so the values are strictly different. In case of a blend of polystyrene and polyphenylene oxide, the anisotropy is negative when Δn (450) / Δn (550) <1. Although the values are different, they are considered to correspond to cases 2 and 4 in Table 4.
[0044]
Although the above discussion has been described with respect to two components, the above concept is valid even with three or more components. For example, in a system in which the component having positive optical anisotropy is two components and the component having negative anisotropy is one component, the birefringence value and the birefringence dispersion value of the component having positive optical anisotropy Etc. can be corrected by a volume fraction between two components having positive anisotropy, etc., and these two components can be regarded as one component, and the concept of the following consideration of the above formula (a) can be applied.
[0045]
In addition, the explanation based on the above formula (a) has been explained as a blend of the polymers A and B. However, the concept of the above-mentioned consideration holds true also in the case of a copolymer containing different monomer units. If the above-mentioned concept is applied by assuming that it is composed of a homopolymer based on one monomer unit (polymer A) and a homopolymer based on a second monomer unit different from the first monomer unit (polymer B) Good.
[0046]
Furthermore, the concept of the above consideration can be similarly applied to a polymer blend of a homopolymer and a copolymer or a polymer blend of copolymers. That is, in this case, the polymer blend is divided into the monomer units constituting the component polymer, and the polymer blend is regarded as an aggregate of homopolymers composed of the respective monomer units. The above consideration may be applied by regarding the combination of Component A consisting of a group of homopolymers having anisotropy and Component B consisting of a group of homopolymers having negative anisotropy.
[0047]
For example, in a copolymer of polymers X and Y having positive optical anisotropy and monomer units x and z having negative optical anisotropy, x has positive optical anisotropy and z is In the case of having negative optical anisotropy, the component having positive optical anisotropy is considered to be composed of X, Y and x, and the birefringence value and birefringence dispersion value are positively anisotropic. These three components are regarded as one component A, and the component having negative anisotropy is regarded as a polymer B composed of the monomer unit z. For the component B, the concept of the above consideration (a) may be applied.
[0048]
In the single polymer based on the first or second monomer unit, when the single polymer is a polycarbonate, the polycarbonate is generally obtained by polycondensation of a dihydroxy compound and phosgene. Therefore, from the viewpoint of polymerization, it is composed of bisphenol. Dihydroxy compound and phosgene become monomers. Thus, in the case of polycarbonate, the monomer unit refers to a portion derived from bisphenol and does not include a portion derived from phosgene.
[0049]
In general, the optical elastic modulus measured near room temperature is often discussed in relation to the phase difference that occurs after film formation or stretching process in the case of film formation after some polymer molding, but in reality it is not always the case. Absent. Rather, retardation is the product of birefringence and film thickness, and birefringence is the product of intrinsic birefringence and orientation function. From the standpoint of molecular design, it is necessary to consider this intrinsic birefringence and orientation function. There is. In order to obtain a transparent film having a small retardation value with high productivity, it is important to first reduce this intrinsic birefringence. Since the orientation function is a factor related to the orientation of the polymer, it is believed to depend on the molding process. When considering the solution cast film forming process normally used as a film forming process, it is necessary to lower the orientation function in the process when the intrinsic birefringence is large, and there are disturbance factors such as uneven temperature and uneven tension. This leads to non-uniformity of the orientation function, and the resulting transparent film has a large retardation. On the other hand, if the intrinsic birefringence is small, it is expected that a uniform and uniform phase difference can be obtained even if the orientation function is somewhat uneven. In the present invention, a material having a small intrinsic birefringence is used.
[0050]
[Form of the present invention]
The transparent film for protecting a polarizing plate in the present invention comprises a single transparent film made of a thermoplastic resin having a water absorption of 1% by weight or less, and satisfies the above formulas (1) to (3) at the same time. In the above formula (1), preferably, | R (550) | ≦ 10 nm, more preferably | R (550) | ≦ 5 nm. In the above formula (2), preferably, | K (550) | ≦ 25 nm, more preferably | K (550) | ≦ 10 nm. In the above formulas (1) and (2), the phase difference is defined at a measurement wavelength of 550 nm, but it is preferable that the above value is satisfied by measurement at a visible light wavelength.
[0051]
Since the principle of the material for satisfying the above characteristics with one transparent film has already been described, specific materials will be described below.
[0052]
The water absorption of the transparent film for protecting a polarizing plate of the present invention is required to be 1% by weight or less. When the water absorption rate of the transparent film exceeds 1% by weight, there may be a problem in practical use as a protective film for a polarizing plate, particularly in a high temperature and high humidity environment. Particularly preferably, when the selection is made so as to satisfy the condition of 0.5% by weight or less, the wet heat durability may be further improved.
[0053]
Furthermore, the transparent film for protecting a polarizing plate of the present invention preferably has a glass transition temperature of 120 ° C. or higher. If it is less than this, there may be a problem of deformation such as shrinkage during the durability test.
[0054]
The thermoplastic resin constituting the transparent film for protecting a polarizing plate of the present invention is not particularly limited, and is not particularly limited as long as it is a polymer (copolymerization) satisfying the above conditions with one sheet of the film, or a blend thereof. For example, materials having excellent heat resistance, good optical performance, and capable of forming a solution film, such as thermoplastic polymers such as polyarylate, polyester, polycarbonate, polyolefin, polyether, polysulfine copolymer, polysulfone, and polyethersulfone Is preferred.
[0055]
When this thermoplastic polymer is used, as described above, a blend polymer composed of a polymer having a positive refractive index anisotropy and a polymer having a negative refractive index anisotropy, a positive refractive index anisotropic A copolymer composed of a high molecular weight monomer unit and a high molecular weight monomer unit having negative refractive index anisotropy is more preferable. Two or more kinds thereof may be combined, or one or more kinds of blend polymers and one or more kinds of copolymers may be used in combination.
[0056]
Since blend polymers need to be optically transparent, it is preferable that the blends are compatible or the refractive indices of the respective polymers are approximately equal. As specific combinations of blend polymers, for example, poly (methyl methacrylate) as a polymer having negative optical anisotropy, poly (vinylidene fluoride), poly ( A combination with at least one polymer selected from the group consisting of (ethylene oxide) and poly (vinylidene fluoride-co-trifluoroethylene), poly (phenylene oxide) as a polymer having positive optical anisotropy, and negative At least one polymer selected from the group consisting of polystyrene, poly (styrene-co-lauroylmaleimide), poly (styrene-co-cyclohexylmaleimide) and poly (styrene-co-phenylmaleimide) as the polymer having optical anisotropy In combination with poly (s) with negative optical anisotropy (Lene-co-maleic anhydride) and a polycarbonate having positive optical anisotropy, poly (acrylonitrile-co-butadiene) having positive optical anisotropy and poly (acrylic-co-butadiene) having negative optical anisotropy A combination of (acrylonitrile-co-styrene) and a combination of a polycarbonate having a positive optical anisotropy and a polycarbonate having a negative optical anisotropy can be suitably exemplified, but the invention is not limited thereto. In particular, from the viewpoint of transparency, blend polymers obtained by combining polystyrene and poly (phenylene oxide) such as poly (2,6-dimethyl-1,4-phenylene oxide), polycarbonate having positive optical anisotropy, and negative A blend obtained by combining a polycarbonate having optical anisotropy of 5 is preferred. In the former case, it is preferable that the ratio of the polystyrene occupies 67% by weight or more and 75% by weight or less. In the latter case, it is preferable to blend a polycarbonate having bisphenol A having positive optical anisotropy as a diol component and a polycarbonate mainly having a fluorene skeleton having bisphenol fluorene as a diol component. The content of the bisphenol fluorene component in the entire blend is preferably 30 to 90 mol%.
[0057]
Examples of the copolymer include poly (butadiene-co-polystyrene), poly (ethylene-co-polystyrene), poly (acrylonitrile-co-butadiene), poly (acrylonitrile-co-butadiene-co-styrene), and polycarbonate. A polymer, a polyester copolymer, a polyester carbonate copolymer, a polyarylate copolymer, or the like can be used. In particular, since a segment having a fluorene skeleton can have negative optical anisotropy, a polycarbonate copolymer, a polyester copolymer, a polyester carbonate copolymer, a polyarylate copolymer, and the like having a fluorene skeleton are more preferably used.
[0058]
The polymer material may be a blend of two or more types of copolymers, or may be a blend of one or more types of copolymers and the blend or other polymer, or two or more types of blends. Or a blend of other polymers or copolymers. In these cases, the total content of the bisphenolfluorene component is preferably 30 to 90 mol%.
[0059]
A polycarbonate copolymer produced by reacting a bisphenol with a carbonate ester-forming compound such as phosgene or diphenyl carbonate is excellent in transparency, heat resistance and productivity, and can be particularly preferably used. The polycarbonate copolymer is preferably a copolymer having a structure having a fluorene skeleton. The component having a fluorene skeleton is a repeating unit represented by the formula (I), and is preferably contained in an amount of 1 to 99 mol% of the entire repeating unit.
[0060]
Specifically, the following formula (I)
[0061]
[Chemical 8]

[0062]
(In the above formula (I), R₁~ R₈Are each independently at least one selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 6 carbon atoms, and X is
[0063]
[Chemical 9]

[0064]
It is. )
30 to 90 mol% of a repeating unit represented by the following formula (II)
[0065]
[Chemical Formula 10]

[0066]
(In the above formula (II), R₉~ R₁₆Are each independently at least one selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 22 carbon atoms, and Y represents the following group of formulas
[0067]
Embedded image

[0068]
(Where R in Y₁₇~ R₁₉, R_{twenty one}And R_{twenty two}Are each independently a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 22 carbon atoms, R₂₀And R_{twenty three}Are each independently selected from hydrocarbon groups having 1 to 20 carbon atoms, and Ar is at least one group selected from aryl groups having 6 to 10 carbon atoms. )
A polycarbonate copolymer in which the repeating unit represented by occupies 70 to 10 mol% of the whole is exemplified.
[0069]
In the above formula (I), R₁~ R₈Are independently selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 6 carbon atoms. Examples of the hydrocarbon group having 1 to 6 carbon atoms include alkyl groups such as a methyl group, an ethyl group, an isopropyl group, and a cyclohexyl group, and an aryl group such as a phenyl group. Among these, a hydrogen atom and a methyl group are preferable.
[0070]
In the above formula (II), R₉~ R₁₆Are independently selected from a hydrogen atom, a halon atom, and a hydrocarbon group having 1 to 22 carbon atoms. Examples of the hydrocarbon group having 1 to 22 carbon atoms include alkyl groups having 1 to 9 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, and a cyclohexyl group, and aryl groups such as a phenyl group, a biphenyl group, and a terphenyl group. It is done. Among these, a hydrogen atom and a methyl group are preferable.
[0071]
In Y of the above formula (II), R₁₇~ R₁₉, R_{twenty one}And R_{twenty two}Are each independently at least one group selected from a hydrogen atom, a halogen atom, and a hydrocarbon group having 1 to 22 carbon atoms. Examples of the hydrocarbon group include the same ones as described above. R₂₀And R_{twenty three}Are each independently selected from hydrocarbon groups having 1 to 20 carbon atoms, and examples of such hydrocarbon groups include those described above. Ar is an aryl group having 6 to 10 carbon atoms such as a phenyl group or a naphthyl group.
[0072]
The transparent film in the present invention preferably uses a polycarbonate having a fluorene skeleton. Examples of the polycarbonate having a fluorene skeleton include a polycarbonate copolymer comprising a repeating unit represented by the above formula (I) and a repeating unit represented by the above formula (II), and a repeating unit represented by the above formula (I). A blend of the polycarbonate and the polycarbonate composed of the repeating unit represented by the above formula (II) is good. The content of the above formula (I), that is, the copolymer composition in the case of the copolymer, 30 to 90 mol% of the whole polycarbonate is preferable. If it is out of this range, it is difficult to uniformly obtain a retardation film having a small retardation value. The content of the above formula (I) is preferably from 35 to 85 mol%, more preferably from 50 to 80 mol%, based on the whole polycarbonate.
[0073]
The copolymer may be a combination of two or more repeating units represented by the above formulas (I) and (II). In the case of a blend, two or more of the repeating units may be combined.
[0074]
Here, the molar ratio can be determined for the entire polycarbonate bulk constituting the transparent film, for example, by a nuclear magnetic resonance (NMR) apparatus, regardless of the copolymer or blend.
[0075]
As the polycarbonate having the fluorene skeleton, the following formula (III)
[0076]
Embedded image

[0077]
(In the above formula (III), R_{twenty four}And R_{twenty five}Are each independently at least one selected from a hydrogen atom and a methyl group. )
35 to 85 mol% of a repeating unit represented by the following formula (IV)
[0078]
Embedded image

[0079]
(In the above formula (IV), R₂₆And R₂₇Are each independently selected from a hydrogen atom and a methyl group, and Z is a group of the following formulae:
[0080]
Embedded image

[0081]
Is at least one group selected from the group consisting of )
It is particularly preferable to use a polycarbonate copolymer and / or a blend in which 65 to 15% of the total.
[0082]
The above copolymer and / or blend can be produced by a known method. As the polycarbonate, a method by polycondensation of a dihydroxy compound and phosgene, a melt polycondensation method or the like is preferably used. In the case of a blend, a compatible blend is preferable, but even if it is not completely compatible, light scattering between components can be suppressed and transparency can be improved by adjusting the refractive index between components.
[0083]
The intrinsic viscosity of the polycarbonate is preferably 0.3 to 2.0 dl / g. If it is less than 0.3, there is a problem that it becomes brittle and the mechanical strength cannot be maintained, and if it exceeds 3.0, the solution viscosity becomes too high, so problems such as die line formation in solution casting, and purification at the end of polymerization are difficult. There is a problem of becoming.
[0084]
The transparent film for protecting a polarizing plate of the present invention needs to have high transparency. Specifically, the haze value is 3% or less, and the total light transmittance is 80% or more, preferably 85% or more at a measurement wavelength of 380 to 780 nm. It is preferable that Further, it is preferably colorless and transparent, but L described in JISZ-8279^*a^*b^*Of the color system, b using a 2 ° visual field C light source^*Is preferably 1.3 or less, more preferably 0.9 or less.
[0085]
The transparent film for protecting a polarizing plate of the present invention further contains an ultraviolet absorber such as phenyl salicylic acid, 2-hydroxybenzophenone, triphenyl phosphate, a bluing agent for changing the color, an antioxidant, and the like. Also good.
[0086]
As a method for producing a transparent film for protecting a polarizing plate of the present invention, a known melt extrusion method, solution casting method and the like are used, but the solution casting method is more preferably used from the viewpoint of film thickness unevenness, appearance and the like. As the solvent in the solution casting method, methylene chloride, dioxolane and the like are preferably used. The amount of residual methyl chloride is preferably 0.5% by weight or less, more preferably 0.3% by weight or less, and still more preferably 0.1% by weight or less.
[0087]
The transparent film thus obtained may be stretched or the like to orient the polymer chain so as to have desired optical properties as necessary. As the stretching method, a known stretching method can be used, but longitudinal uniaxial stretching is preferred. At this time, a plasticizer can be added to the film for the purpose of improving stretchability. Additives such as plasticizers can change the retardation wavelength dispersion, but the addition amount is preferably 10 wt% or less, more preferably 3 wt% or less with respect to the polymer solid content.
[0088]
The film thickness of the polarizing plate protecting transparent film of the present invention is preferably 5 μm to 200 μm, more preferably 10 to 120 μm.
[0089]
It is known that a transparent film having optical anisotropy generally gives different phase difference values to incident light from an oblique angle as compared to front incident light. Here, the three-dimensional refractive index of the polymer material is represented by nx, ny, nz, and the respective definitions are as follows:
nx: refractive index in the main orientation direction in the transparent film plane
ny: Refractive index in the direction perpendicular to the main orientation direction in the transparent film plane
nz: refractive index in the normal direction of the transparent film surface
And Here, the main orientation direction means, for example, the flow direction of the film, and refers to the orientation direction of the polymer main chain in terms of chemical structure. Here, the optical anisotropy is called positive when nx> nz and the optical anisotropy is negative when nx <nz. This three-dimensional refractive index is measured by ellipsometry, which is a technique for analyzing the polarization state of outgoing light obtained by making polarized light incident on a transparent film. In the present invention, the optical anisotropy of the transparent film is determined by the refractive index. The three-dimensional refractive index is obtained by a method of obtaining an ellipsoid by a known refractive index ellipsoid formula. Since this three-dimensional refractive index is dependent on the wavelength of the light source to be used, it is preferably defined by the light source wavelength to be used. As a method of expressing optical anisotropy using this three-dimensional refractive index, the following formula (8)
[0090]
[Expression 7]
Nz = (nx-nz) / (nx-ny) (8)
However, if the three-dimensional refractive index is defined using this, when Nz is in the range of 0.3 to 1.5, the dependency of the retardation value on the incident angle becomes very small. In particular, when Nz = 0.5, the dependency of the phase difference value on the incident angle substantially disappears, and the same phase difference value is given no matter what angle the light enters.
[0091]
According to the above definition, the slow axis of a transparent film having positive optical anisotropy is nx and the fast axis is ny.
[0092]
In order to reduce the retardation of a transparent film used as a transparent film for protecting a polarizing plate of the present invention as a short wavelength, it is an indispensable condition to have a specific chemical structure as described above, and the retardation wavelength dispersion is considerable. It should be noted that the portion is determined by its chemical structure, but will also vary depending on the additive, film forming conditions, blend state, molecular weight, and the like.
[0093]
As a configuration of the polarizing plate using the transparent film for protecting a polarizing plate of the present invention, the transparent film is installed on both sides or one side of the polarizing layer, and adhesion between the polarizing layer and the transparent film is an adhesive or An adhesive is used. A schematic cross-sectional view of a polarizing plate in which the transparent film is installed on both sides of the polarizing layer is shown in FIG. In order to improve the adhesion, a coating layer, a corona treatment, a hydrophilic treatment or the like may be performed on the transparent film. Moreover, when the transparent film for polarizing plate protection of this invention is installed in the outermost surface of a display apparatus, you may perform a hard-coat layer, an antireflection layer, a glare-proof process, etc., for example. In this case, the polarizing layer refers to a layer that generates polarized light from non-polarized light.For example, a polymer obtained by dispersing and aligning iodine or a dichroic dye in a polymer such as polyvinyl alcohol, a polymer having dichroism, or a polyacetylene is aligned. It refers to things that have been made.
[0094]
【The invention's effect】
As described above, according to the present invention, a transparent film for protecting a polarizing plate having a small optical anisotropy and a smaller retardation as the wavelength becomes shorter with a single transparent film made of a thermoplastic resin having a water absorption of 1% by weight or less has high mass productivity. For example, a polarizing plate excellent in durability and polarization performance can be realized by using this for a polarizing plate.
[0095]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
(Evaluation method)
The material characteristic values and the like described in the present specification are obtained by the following evaluation methods.
(1) Measurement of phase difference value (R = Δn · d (nm)), K value
The retardation R value and K value, which are products of the birefringence Δn and the film thickness d of the protective film for polarizing plate, were measured by a trade name “M150” manufactured by JASCO Corporation, which is a spectroscopic ellipsometer. The R value was measured with the incident light beam and the film surface orthogonal. The K value (nm) is determined by changing the angle between the incident light beam and the film surface, measuring the phase difference value at each angle, and curve fitting with a known refractive index ellipsoid equation to obtain a three-dimensional refractive index. Nx, ny, and nz were obtained and substituted into the following equation (7).
[0096]
[Equation 8]
K = (nz− (nx + ny) / 2) * d (7)
[0097]
(2) Measurement of water absorption
Except that the film thickness was 130 ± 50 μm in the dried film state, the measurement was performed in accordance with “Test method for water absorption and boiling water absorption of plastics” described in JIS K 7209. The size of the test piece was 50 mm square, and the weight change was measured after the sample was immersed for 24 hours at a water temperature of 25 ° C. This is the so-called saturated water absorption, and the unit is% by weight.
[0098]
(3) Measurement of glass transition temperature (Tg) of polymer
It was measured by “DSC2920 Modulated DSC” manufactured by TA Instruments. It was measured in the state of flakes or chips after resin polymerization, not after film formation.
[0099]
(4) Film thickness measurement
Measurement was performed with an electronic micro manufactured by Anritsu.
[0100]
(5) Measurement of the copolymerization ratio
It was measured by proton NMR of “JNM-alpha600” manufactured by JEOL Ltd. In particular, in the case of a copolymer of bisphenol A and biscresol fluorene, heavy benzene was used as a solvent, and calculation was performed from the proton intensity ratio of each methyl group.
[0101]
(6) Measurement of transmittance
The product name “U-3500”, a spectrophotometer manufactured by Hitachi, Ltd. was used. The measurement wavelength is 380 to 780 nm, but in the examples, the measurement wavelength is 550 nm.
[0102]
Moreover, the monomer structure of the polycarbonate used by the following example and the comparative example is described below.
[0103]
Embedded image

[0104]
[Example 1]
A reaction vessel equipped with a stirrer, a thermometer and a reflux condenser is charged with an aqueous sodium hydroxide solution and ion-exchanged water, and the monomers [A] and [F] having the above structure are dissolved in the molar ratio shown in Table 2 and a small amount. Of hydrosulfite was added. Next, methylene chloride was added thereto, and phosgene was blown in at about 20 ° C. over about 60 minutes. Further, p-tert-butylphenol was added for emulsification, and then triethylamine was added and stirred at 30 ° C. for about 3 hours to complete the reaction. After completion of the reaction, the organic phase was collected, and methylene chloride was evaporated to obtain a polycarbonate copolymer. The composition ratio of the obtained copolymer was almost the same as the monomer charge ratio.
[0105]
This copolymer was dissolved in methylene chloride to prepare a dope solution having a solid concentration of 20% by weight. A cast film was produced from this dope solution to obtain a transparent film.
[0106]
Table 2 summarizes the measurement results. The R and K values of this film were small, and the width direction was measured with a 1 m wide film, and the range of variation in R (550) was ± 0.5 nm. It was confirmed that the shorter the wavelength in the measurement wavelength range of 400 to 700 nm, the smaller the phase difference and the positive refractive index anisotropy. It turned out that it is suitable as a polarizing plate protective film.
[0107]
[Example 2]
A polycarbonate copolymer was obtained in the same manner as in Example 1 except that the monomers listed in Table 2 were used. The composition ratio of the obtained copolymer was almost the same as the monomer charge ratio. A film was formed in the same manner as in Example 1 to obtain a transparent film. Table 2 summarizes the measurement results. Further, it was confirmed that the shorter the wavelength in the measurement wavelength range of 400 to 700 nm, the smaller the phase difference and the positive the refractive index anisotropy.
[0108]
[Example 3]
A polycarbonate copolymer was obtained in the same manner as in Example 1 except that the monomers listed in Table 2 were used. The composition ratio of the obtained copolymer was almost the same as the monomer charge ratio. A film was formed in the same manner as in Example 1 to obtain a transparent film. Table 2 summarizes the measurement results. Further, it was confirmed that the shorter the wavelength in the measurement wavelength range of 400 to 700 nm, the smaller the phase difference and the positive the refractive index anisotropy.
[0109]
[Example 4]
A polycarbonate copolymer was obtained in the same manner as in Example 1 except that the monomers listed in Table 2 were used. The composition ratio of the obtained copolymer was almost the same as the monomer charge ratio. A film was formed in the same manner as in Example 1 to obtain a transparent film. Table 2 summarizes the measurement results. Further, it was confirmed that the shorter the wavelength in the measurement wavelength range of 400 to 700 nm, the smaller the phase difference and the positive the refractive index anisotropy.
[0110]
[Example 5]
A polycarbonate copolymer was obtained in the same manner as in Example 1 except that the monomers listed in Table 2 were used. The composition ratio of the obtained copolymer was almost the same as the monomer charge ratio. A film was formed in the same manner as in Example 1 to obtain a transparent film. Table 2 summarizes the measurement results. Further, it was confirmed that the shorter the wavelength in the measurement wavelength range of 400 to 700 nm, the smaller the phase difference and the positive the refractive index anisotropy.
[0111]
[Example 6]
A polycarbonate copolymer was obtained in the same manner as in Example 1 except that the monomers listed in Table 2 were used. The composition ratio of the obtained copolymer was almost the same as the monomer charge ratio. A film was formed in the same manner as in Example 1 to obtain a transparent film. Table 2 summarizes the measurement results. Further, it was confirmed that the shorter the wavelength in the measurement wavelength range of 400 to 700 nm, the smaller the phase difference and the positive the refractive index anisotropy.
[0112]
[Example 7]
Polystyrene (Wako Pure Chemical Industries, Ltd.) as a polymer having negative refractive index anisotropy, and polyphenylene oxide (poly (2,6-dimethyl 1,4-phenylene) as a polymer having positive refractive index anisotropy Oxide) Wako Pure Chemical Industries, Ltd.) was dissolved in chloroform at a ratio of 70 and 30% by weight, respectively, to prepare a dope solution having a solid content concentration of 18% by weight. A cast film was produced from this dope solution to obtain a transparent film.
[0113]
Table 2 summarizes the optical characteristic measurement results. This film was confirmed to have a smaller phase difference and a negative refractive index anisotropy as the wavelength was shorter at a measurement wavelength of 400 to 700 nm. It turned out that it is suitable as a transparent film for polarizing plate protection.
[0114]
For reference, FIG. 6 shows the relationship between the birefringence wavelength dispersion coefficient and the volume fraction of polyphenylene oxide when the blend ratio of polystyrene and polyphenylene oxide is changed. It can be seen that there is a region where the optical anisotropy is negative and the birefringence wavelength dispersion coefficient is smaller than 1 in the region where the polyphenylene oxide is small. On the other hand, the value is larger than 1 in a region where the refractive index anisotropy is large in polyphenylene oxide.
[0115]
Next, FIG. 7 shows the relationship between the volume fraction and the birefringence wavelength dispersion coefficient as shown in FIG. 6 calculated using the above-described equation (c). Figure 7 shows the intrinsic birefringence of polystyrene and polyphenylene oxide at a wavelength of 550 nm, −0.10, 0.21 (see D. Lefebvre, B. Jasse and L. Monnerie, Polymer 23 706-709 (1982)), and The value of R (450) / R (550) was calculated as 1.06 and 1.15. It can be said that FIG. 6 and FIG. 7 agree well. The densities of polystyrene and polyphenylene oxide are 1.047 and 1.060 g / cm, respectively.^ThreeIt was.
[0116]
[Table 2]

[0117]
[Comparative Example 1]
Using a commercially available polycarbonate made of polycondensation of commercially available bisphenol A and phosgene (“Panlite C1400” manufactured by Teijin Chemicals), a film was formed in the same manner as in Example 1 to obtain a transparent film. Table 3 summarizes the measurement results. It was found that the K value was negatively large and the shorter the measurement wavelength, the greater the phase difference, which was not preferable as the polarizing plate protective film intended in the present invention.
[0118]
[Comparative Example 2]
A film was formed in the same manner as in Example 1 using “ARTON” manufactured by JSR, which is a commercially available norbornene resin. Table 3 summarizes the measurement results. It was found that the K value was negatively large and the shorter the measurement wavelength, the larger the phase difference, which was not preferable as the polarizing plate protective film intended in the present invention.
[0119]
[Comparative Example 3]
A triacetyl cellulose resin (Wako Pure Chemical Industries, Ltd., intrinsic viscosity [η] 1.335, acetylation degree 2.917) was used, except that the solvent was methylene chloride / methanol (weight ratio 9/1). A film was formed in the same manner as in Example 1. Table 3 summarizes the measurement results. The K value is positively large, the shorter the measurement wavelength is, the larger the absolute value and the phase difference are, and the water absorption is 4% by weight, which is preferable as the polarizing plate protective film intended in the present invention. I found that there was no.
[0120]
[Table 3]

[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an example of a polarizing plate using a transparent film for protecting a polarizing plate of the present invention.
2 is a graph showing the relationship between birefringence wavelength dispersion and volume fraction φA of a two-component blend polymer corresponding to case 1 in Table 1. FIG.
FIG. 3 is a graph showing the relationship between birefringence wavelength dispersion and volume fraction φA of a two-component blend polymer corresponding to case 2 in Table 1.
4 is a graph showing the relationship between birefringence wavelength dispersion and volume fraction φA of a two-component blend polymer corresponding to Case 3 in Table 1. FIG.
FIG. 5 is a graph showing the relationship between birefringence wavelength dispersion and volume fraction φA of a two-component blend polymer corresponding to Case 4 in Table 1.
FIG. 6 is a graph showing the relationship between the volume fraction of polyphenylene oxide and R (450) / R (550) in a blend of polystyrene and polyphenylene oxide. (Actual value)
FIG. 7 is a graph showing the relationship between the volume fraction of polyphenylene oxide and R (450) / R (550) in a blend of polystyrene and polyphenylene oxide. (Calculated values)
[Explanation of symbols]
1: Transparent film for protecting polarizing plate of the present invention
2: Adhesive layer
3: Polarizing layer

Claims (9)

A transparent film made of a thermoplastic resin and having a water absorption of 1% by weight or less, wherein the transparent film has the following condition A or B:
[Condition A]
(I) Polymer monomer unit having positive refractive index anisotropy (hereinafter referred to as first monomer unit) and polymer monomer unit having negative refractive index anisotropy (hereinafter referred to as second monomer) A film composed of a polymer including:
( Ii ) R (450) / R (550) of the polymer based on the first monomer unit is smaller than R (450) / R (550) of the polymer based on the second monomer unit, and
( Iii ) having positive refractive index anisotropy,
[Condition B]
(I) A monomer unit that forms a polymer having positive refractive index anisotropy (hereinafter referred to as a first monomer unit) and a monomer unit that forms a polymer having negative refractive index anisotropy (hereinafter referred to as “first monomer unit”). A second monomer unit)) and a polymer composed of a polymer.
( Ii ) R (450) / R (550) of the polymer based on the first monomer unit is larger than R (450) / R (550) of the polymer based on the second monomer unit, and
( Iii ) having negative refractive index anisotropy,
A transparent film for protecting a polarizing plate, characterized in that the retardation at wavelengths of 450 nm and 550 nm simultaneously satisfies the following formulas (1) to (3):

(Where R (450) and R (550) are in-plane retardations of the transparent film at wavelengths of 450 nm and 550 nm, respectively, and K (550) is K = [nz− (nx + ny) / 2] × d (where nx, ny, and nz are the three-dimensional refractive indexes of the transparent film, which are the refractive indexes in the x-axis, y-axis, and z-axis directions, respectively, and d is the thickness of the film). Value.)   The transparent film for polarizing plate protection according to claim 1, wherein the retardation of the transparent film is smaller as the wavelength is shorter at a wavelength of 400 to 700 nm. Transparent film for polarizing plate protective according to any one of claims 1-2 glass transition temperature of 120 ° C. or more of said transparent film. The transparent film for polarizing plate protection according to claim 1, wherein the transparent film contains a polycarbonate having a fluorene skeleton. Polycarbonate having a fluorene skeleton is represented by the following formula (I)

(In the above formula (I), R _{1 to} R ₈ are each independently at least one selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 6 carbon atoms, and X is

It is. )
30 to 90 mol% of a repeating unit represented by the following formula (II)

(In the above formula (II), R _{9 to} R ₁₆ are each independently at least one selected from a hydrogen atom, a halogen atom, and a hydrocarbon group having 1 to 22 carbon atoms, and Y represents the following group of formulas:

(Here, R _{17 to} R ₁₉ , R ₂₁ and R ₂₂ in Y are each independently at least one selected from a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 22 carbon atoms, and R ₂₀ and R _23. Are each independently at least one selected from hydrocarbon groups having 1 to 20 carbon atoms, and Ar is at least one group selected from aryl groups having 6 to 10 carbon atoms.)
The transparent film for protecting a polarizing plate according to claim 4 , wherein the repeating unit represented by the formula (1) is a polycarbonate copolymer and / or a blend that accounts for 70 to 10 mol% of the whole. A polycarbonate having a fluorene skeleton is represented by the following formula (III)

(In the above formula (III), R ₂₄ and R ₂₅ are each independently at least one selected from a hydrogen atom and a methyl group.)
35 to 85 mol% of a repeating unit represented by the following formula (IV)

(In the above formula (IV), R ₂₆ and R ₂₇ are each independently selected from a hydrogen atom and a methyl group;

Is at least one group selected from the group consisting of )
The transparent film for protecting a polarizing plate according to claim 5 , wherein the repeating unit represented by the formula (1) is a polycarbonate copolymer and / or a blend that accounts for 65 to 15 mol% of the whole. The transparent film is a blend of a polymer having a positive refractive index anisotropy and a polymer having a negative refractive index anisotropy, and the polymer having a positive refractive index anisotropy is poly (2 , 6-dimethyl-1,4-phenylene oxide), according to claim 1, wherein the polymer having a refractive index anisotropy of the negative is and and polystyrene content is 67 wt% to 75 wt% polystyrene Transparent film for polarizing plate protection. The transparent film for polarizing plate protection according to any one of claims 1 to 7 , wherein the transparent film is produced by a solution cast film forming method. A polarizing plate characterized by using a transparent film of any of claims 1-8.

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