JP4105331B2 - Low birefringence optical resin material, production method thereof and application thereof - Google Patents

Description

【００２６】
また文献（３）は、散乱理論および有効媒質理論を基に、球状粒体における分布複屈折性を表す式として下記の式２、並びに当該式２中のＮ（ｒ′）に関する式として下記の式３を提案している。
各式において、ｒは粒体の半径、ｖは分散粒体の体積分率、ｎ_h は粒体分布が疎となる方向の屈折率または粒体分布が密となる方向の屈折率、ｎ₁ は粒体の屈折率、ｎ₂ は媒質の屈折率、Ｌ_h は粒体分布が密となる方向の復極係数または粒体分布が疎となる方向の復極係数、δは分散である。
【００２７】
【数２】

【００２８】
上記の各式における復極係数が実質的に分散粒体間の距離に対応し、従って分散粒体の疎密に対応している。ここで、式１および式２は、後者がより精密であるという点を別にすれば、その意味するところは実質的に同じであると言える。そこで、より簡易な式１に用いて説明すると、この式１において分布複屈折値を与える左辺の項（ｎ_e ² −ｎ_o ² ）の符号は、右辺の項（Ｌ_e −Ｌ_o ）の符号で定まること、換言すれば、粒体分布が密となる方向の復極係数Ｌ_e と、粒体分布が疎となる方向の復極係数Ｌ₀ との大小関係で定まることが分かる。すなわち、分布複屈折は、媒質の屈折率と分散粒体の屈折率との間の大小関係とは無関係に定まり、粒体分布の密となる方向における屈折率が、粒体分布の疎となる方向における屈折率よりも大きくなるように生じる。
【００２９】
また式１から明らかなように、媒質の屈折率ｎ₂ と粒体の屈折率ｎ₁ との差が大きいほど、分布複屈折値が大きくなる。
一方、式２から、粒体のサイズ（半径ｒ）が大きいほど、分布複屈折値が大きくなることが導かれる。
ただし、この場合の復極係数（Ｌ_e およびＬ_o ）、つまり分布による屈折率の異方性には粒体自体の分極異方性も関係している。例えば、粒体が楕円形である場合に、その形状に応じて、その短軸方向よりも長軸方向の屈折率が大きくなるような分極異方性を有していれば、これが分布複屈折に影響を与えることとなる。すなわち、粒体が均一に分散されている或る媒質に外力などが作用されて粒体に疎密分布が生じる場合には、一般的に、形状的異方性を有する粒体は、その分布が疎になる方向にその長軸方向を平行にする状態をとることになり、そのために、長軸方向の相対的に大きな屈折率が、粒体分布の密な方向（長軸方向に直交する方向）における大きな屈折率を相殺するように働く。
【００３０】
すなわち、一般的には、粒体に形状異方性を伴う分極異方性（複屈折性）があると、これにより分布複屈折の発現が抑えられることになる。従って、分布複屈折を効果的に発現させるためには、粒体が分極に関して等方性を有するものであるか、または形状に関して等方性を有することが望ましい。
この場合の形状的等方性は、上記の説明から理解されるように、もし粒体が分極に関して異方性を有する場合には、当該分極異方性を全体として発現させるような規則性のある配向を生じることのない程度に形状に等方性があるということを意味する。そのような等方性の形状の典型的な例は、球形および正多角形である。
【００３１】
而して、本発明の光学樹脂材料は、補償用粒体が均一に混入され分散された状態の高分子樹脂であり、この粒体が混入された高分子樹脂に外力などが加えられてポリマー鎖に配向が生じると、補償用粒体もポリマー鎖の配向運動の影響を受けて必然的にその分布に変化を生じ、しかもこの分布変化の結果、当該補償用粒体は、ポリマー鎖の配向方向に疎で、これと交差する方向に密となる分布で存在する状態となり、従ってこれにより発現される分布複屈折性は、ポリマー鎖の配向方向に関して、常に負となるものとなる。
【００３２】
このような高分子樹脂に対してその分布複屈折性を低減化するような、補償的な分布複屈折が発現されるためには、上記の説明から明らかなように、
（１）補償用粒体のサイズが光の波長よりも小さいこと、すなわち、補償用粒体が、高分子樹脂の透明性を実質的に低下させるような散乱を生じないサイズのものであること、並びに
（２）分極に関して等方性を有する物質よりなる粒体であるか、あるいは形状に関して等方性を有する粒体であること、
が必要である。
【００３３】
補償用粒体のサイズに関係する光の波長は、得られる光学樹脂材料が用いられる光学機器に適用される光の波長を基準として考慮されればよく、可視光またはその近辺の光が用いられる場合には、補償用粒体のサイズは、数百ナノメータ以下であることが必要である。
実際上、このようなサイズレベルの粒体は、その入手が比較的容易である。また、分極に関して等方性を有する粒体も、また形状に関しても等方性を有する粒体も容易に得ることができる。
しかも、このような粒体は、実質的にあらゆる高分子樹脂に補償用粒体として適用することが可能であり、従って、本発明の光学樹脂材料に用いられる高分子樹脂についての選択の自由度はきわめて大きい。その上、このような粒体は、高分子樹脂の有する複屈折性以外の光学的特性に実質的な影響を与えることがなく、また機械的特性などに与える影響も小さい。
【００３４】
以上の説明から理解されるように、本発明は、マトリックスを構成する高分子樹脂中に或る種の物質を添加することにより、当該高分子樹脂において発現される配向複屈折性を低減化しまたは補償する点では、従来の技術と同様であるが、そのような高分子樹脂の配向複屈折性を低減化する複屈折性を発現させるためのメカニズムが全く異なっている。すなわち、従来技術にあっては、添加される低分子物質が高分子樹脂における配向複屈折性とは逆の符号の複屈折性を示すことを利用して、両者の相殺関係により全体として低複屈折性あるいは低異方性を達成するものであるが、本発明では、構造複屈折の一種である分布複屈折を利用するものである。
【００３５】
本発明において、マトリックスを構成するための高分子樹脂は、光学樹脂材料としての用途から、或る程度以上の透明性を有することが必要であるが、基本的に、この高分子樹脂は、これに混入される補償用粒体との関係によって特に制約を受けることがなく、従って当該高分子樹脂の選択の自由度がきわめて大きい。実際には、光学樹脂材料としての一般的な適性を有している高分子樹脂を用いることが好ましく、特に具体的な用途に応じて好適な特性、例えば優れた耐熱性や機械強度などを有するものを用いることが好ましい。
この高分子樹脂に必要とされる透明性の程度は、目的とする光学部品などの用途、あるいは要求される光学特性などによって定まり、特に限定されるものではない。当該高分子樹脂は、それ自体が示す複屈折性の符号が正であっても、負であってもよい。
【００３６】
本発明において用いられる高分子樹脂の具体例としては、ポリエチレン、ポリプロピレンなどのポリオレフィン類、ポリスチレンなどの芳香族ビニルポリマー類、ポリメチルメタクリレートなどのポリ（メタ）アクリル酸エステル類、ポリフェニレンオキサイド、ポリカーボネート類、ポリビニルクロライド、ポリエチレンテレフタタレート、ポリアリレート、ポリエーテルスルフオン、ポリエチレンナフタレート、ポリメチルペンテン−１、脂環式ポリオレフィン類（例えばジシクロペンタジエン系ポリオレフィンやノルボルネン系ポリオレフィンなどの環状オレフィンの開環（共）重合体、その水素添加（共）重合体、環状オレフィンと不飽和二重結合含有化合物との飽和共重合体など）、例えばトリシクロデカニルメタクリレート、シクロヘキシルメタクリレート、イソボルニルメタクリレートなどの脂環式（メタ）アクリレートとメチルメタクリレートなどの（メタ）アクリル酸エステルとの共重合体、ポリスルホン、ポリエーテルイミド、非晶性ポリアミド、ポリフェニレンエーテル、並びに環状オレフィン、シクロペンタジエン、芳香族ビニル化合物のカチオン（共）重合体の水素添加重合体、その他を挙げることができる。
以上のうち、好ましい光学特性を有するものとしては、例えばポリメチルメタクリレート、或る種のポリカーボネート、並びに脂環式ポリオレフィン系重合体を挙げることができる。
【００３７】
以上の高分子樹脂のうち、単独での配向複屈折性の程度が大きい重合体では、補償用粒体を多量に添加することが必要となり、その結果、得られる光学樹脂材料の透明性が低下する場合がある。
然るに、脂環式ポリオレフィン系重合体は、通常、小さな正の複屈折性を示す重合体であるために混入すべき補償用粒体の量が少なくてよく、従って、高い透明性、耐熱性に加えて低複屈折性を兼ね備えた光学樹脂材料が得られるので、きわめて好ましい。
【００３８】
脂環式ポリオレフィン系重合体の好ましい例としては、下記一般式（１）に示すノルボルネン誘導体よりなるモノマー若しくはこのモノマーおよびこれと共重合可能な共重合性モノマーを開環重合させて得られる開環重合体、またはこのような開環重合体を更に水素添加して得られる水素添加重合体を挙げることができる。このようなモノマーの開環重合反応は、通常、メタセシス重合触媒によって行われる。
【００３９】
【化１】

〔式中ＡおよびＢは水素原子または炭素数１〜１０の炭化水素基であり、ＸおよびＹは水素原子または一価の有機基を示し、ｍは０または１である。〕
【００４０】
このようなノルボルネン環を有するモノマーのうち、上記一般式（１）におけるＸまたはＹが式−（ＣＨ₂ ）_n ＣＯＯＲ¹ で表わされるカルボン酸エステル基であるモノマーは、得られる開環重合体が、高いガラス転移温度と低い吸湿性を有するものとなる点で好ましい。このカルボン酸エステル基よりなる極性置換基は、モノマーの１分子当たりに１個含有されることが、得られる開環重合体の吸湿性が低くなる点で好ましい。
【００４１】
また、式−（ＣＨ₂ ）_n ＣＯＯＲ¹ で示されるカルボン酸エステル基のうち、ｎの値が小さいものほど、得られる開環重合体のガラス転移温度が高くなるので好ましく、更にｎが０であるモノマーは、その合成が容易である点で、また、得られる開環重合体に良好な特性が得られる点で好ましい。
上記の式において、Ｒ¹ は炭素数１〜２０の炭化水素基であるが、炭素数が多くなるほど得られる重合体の吸湿性が小さくなる点では好ましい。しかし、得られる重合体のガラス転移温度とのバランスの点から、炭素数が１〜４の鎖状アルキル基または炭素数が５以上の（多）環状アルキル基であることが好ましく、特にメチル基であることが好ましい。
更に、カルボン酸エステル基が結合した炭素原子に、同時に炭素数１〜１０の炭化水素基が置換基として結合されているモノマーは、得られる重合体のガラス転移温度を低下させずに吸湿性を低下させるので好ましい。そして、特にこの置換基がメチル基であるモノマーは、その合成が容易な点で好ましい。
上記のモノマーのうちでは、一般式（１）においてｍが１であるテトラシクロドデセン誘導体が、ガラス転移点の高い重合体が得られる点で好ましい。
【００４２】
上記の一般式（１）で示されるもののうち、好ましい化合物の例としては、８−カルボキシメチルテトラシクロ［4.4.0.1^2,5.1^7,10］−３−ドデセン、８−メチル−８−カルボキシメチルテトラシクロ［4.4.0.1^2,5.1^7,10］−３−ドデセン、５−カルボキシメチル−ビシクロ［2.2.1 ］−２−ヘプテンなどを挙げることができる。
【００４３】
上記のモノマーは、これと共重合可能なモノマーとを開環共重合させることができ、そのような共重合体を用いることもできる。
上記の開環重合体が水素添加される場合においては、水素添加率は高いことが好ましく、少なくとも９０モル％以上、特に実質上１００モル％であることが望ましい。
上記の開環重合体またはその水素添加重合体の分子量は、ポリスチレン換算による重量平均分子量で２００００〜５０００００であることが好ましい。
【００４４】
本発明において、補償用粒体としては、上記の条件を満たす粒体であれば、広範な材料の中から自由に選択することができる。
補償用粒体のサイズは、既述のように、当該光学樹脂材料による光学部品または光学要素に適用される光の波長より小さいサイズであればよく、例えば当該光が可視光である場合には数百ナノメータ以下のサイズ、例えば５０〜３００ｎｍ程度であればよい。また、適用される光がレーザ光である場合には、その波長に応じたサイズの補償用粒体を用いればよい。補償用粒体のサイズが過大である場合には、得られる光学樹脂材料は、補償用粒体の存在によって透明性が低下したものとなる。
【００４５】
また補償用粒体は、分極に関して等方性を有する物質よりなるものであるか、分極に関して等方性を有しない物質よりなる場合には、形状に関して等方性を有する粒体であることが必要である。
分極に関して等方性を有する物質の具体例としては、アダマンタン、デンドリマーなどの等方性有機化合物を挙げることができる。
【００４６】
一方、形状に関して等方性を有する粒体とは、典型的には、例えば球状や正多角形のような等方性の形状を有するものであるが、実質的に等方性の形状を有するものであればよく、その程度は、その長径に対する短径の比が例えば１／１０以上であればよい。
このような粒体の物質の具体例としては、例えばシリカ、酸化アルミニウム、酸化チタン、酸化鉄、酸化セリウム、酸化イットリウム、酸化マンガン、酸化ジルコニウム、コバルトブルー、酸化インジウム、酸化マグネシウム、酸化ネオジウム、酸化ホルミウム、酸化銅、酸化アルミニウムと酸化マグネシウムの複合酸化物などの無機化合物の粒体を挙げることができる。
これらの無機化合物は、光の波長よりも小さいサイズの粒体とすることが可能であって、しかも形状が等方性を有する粒体を得ることが可能である。
【００４７】
高分子樹脂に対する補償用粒体の混入割合は、高分子樹脂の配向複屈折性の低減化に有効な割合であればよく、特に限定されるものではないが、通常、高分子樹脂に対して０．００１〜２０重量％であり、例えば０．０１〜１０重量％の範囲である。この補償用粒体の混入割合は、目的とする効果が得られるのであれば少ないことが望ましく、補償用粒体の混入割合が高くなると、得られる光学樹脂材料の透明性、機械的強度、耐熱性などの当該高分子樹脂の有する固有の特性が低下するおそれがある。
【００４８】
本発明の低複屈折性光学樹脂材料を製造するためには、重合反応によって透明性を有する高分子樹脂を生成するモノマーまたはその組成物を用意し、この重合性材料の重合反応を開始する前の段階で補償用粒体を混入し、十分に分散させ、適宜の重合開始剤、連鎖移動剤などを添加した後、加熱あるいは紫外線照射などのエネルギーの供給を行なうことによって重合反応を開始させて進行させ、これにより光学樹脂材料を得る方法を採用することができる。
【００４９】
ここに、重合開始剤や連鎖移動剤の種類および量は、通常の重合反応の場合と同様の基準に従って選択すればよい。例えば、熱重合による場合においては、熱重合開始剤としてべンゾイルパーオキサイドなどの過酸化物を使用することができる。また、紫外線照射による場合には、紫外線ラジカル重合開始剤であるべンゾインメチルエーテルなどを使用することができる。連鎖移動剤としては、いずれの場合にも、ノルマルブチルメルカプタンなどを使用することができる。
この製造方法によれば、重合反応の完了によって、補償用粒体が混入された高分子樹脂を直接的に製造することができる点で有利である。
【００５０】
また、高分子樹脂を生成するモノマーまたはその組成物の重合反応の開始後でかつ完了前の段階において、すなわち重合反応が或る程度遂行されて重合性のオリゴマーが存在する状態の重合反応系に補償用粒体を混入して十分に分散させ、その後、重合反応を完結する方法であってもよい。
この製造方法においても、重合反応の完了によって、補償用粒体が混入された高分子樹脂を直接的に製造することができる。
【００５１】
以上の方法においては、補償用粒体は、当該モノマーまたはその組成物あるいは生成される高分子樹脂に対して親和性の高い表面処理剤（バインダー）によって予め表面処理が施されていることが好ましく、これにより、当該補償用粒体の、マトリックスを構成する高分子樹脂における分散性を高いものとすることができる。この表面処理剤による処理は、重合反応と一連の工程として行うことも可能である。
【００５２】
また、本発明においては、重合反応によって透明性を有する高分子樹脂を製造し、これを加熱溶融させてこれに補償用粒体を添加して混練する方法により、高分子樹脂中に補償用粒体が均一に分散されてなる低複屈折性光学樹脂材料を製造することができる。
【００５３】
あるいは、高分子樹脂を適当な溶媒中に溶解させて得られる溶液中に補償用粒体を添加して均一に分散させ、その後溶媒を蒸発処理などによって除去する方法によっても、目的とする光学樹脂材料を製造することができる。
このような高分子樹脂の溶液に補償用粒体を混入する方法によれば、微粉末状の補償用粒体を十分に均一に分散させることが容易であり、しかも、高分子樹脂を加熱する必要がないためにその熱劣化が生ずることがなく、また、当該高分子樹脂の有する光学特性および機械的特性が損なわれないために、結果として良好な特性の光学樹脂材料が得られる。また、補償用粒体が分散された溶液を、そのままの状態でフィルムなどの製品の製造に供することも可能である。
また、これらの方法においても、補償用粒体は、適宜の表面処理剤によって予め表面処理が施されているものを用いることが好ましい。
【００５４】
以上のような方法によって得られる補償用粒体が混入された光学樹脂材料は、そのままの状態では、通常、高分子樹脂のポリマー鎖が配向されていないために複屈折性を示さないものである。
そして、この補償用粒体が混入された光学樹脂材料は、各種の光学部品や光学材料のための原料として用いられるが、通常の光学樹脂材料の場合と同様に、実用性のある製品の製造に供するために、適当な手段によってぺレット化されることが好ましい。このペレット化された光学樹脂材料は、射出成形あるいは押し出し成形などの、量産性に優れた通常の成形技術によって所望の形状に成形加工されて製品とされる。
【００５５】
このような成形製品を形成する高分子樹脂のマトリックスにおいては、成形工程における外力の作用などによってそのポリマー鎖が特定の方向に配向し、従って配向複屈折性が生じるが、同時に、当該高分子樹脂に混入されている補償用粒体が、当該高分子樹脂体のポリマー鎖の配向方向に疎で当該配向方向と交差する方向に密となる分布で存在する状態となる結果、当該補償用粒体による分布複屈折性が生じ、この分布複屈折性によって高分子樹脂における配向複屈折性が補償されるため、当該光学樹脂材料全体としての複屈折性は、高分子樹脂に固有の配向複屈折性が低減化されたものとなる。
【００５６】
例えば、射出成形工程においては、金型の壁面付近や金型のゲート付近で高分子樹脂に高剪断応力が発生するためにポリマー鎖の配向が生じ、また、押出し成形工程においては、押出し時や引き取り時などに高分子樹脂のポリマー鎖に配向が生じるが、これらのポリマー鎖の配向による配向複屈折性が補償的に低減化される。
また、補償用粒体が混入された高分子樹脂よりなるフィルムを延伸処理する場合にも、当該高分子樹脂のポリマー鎖の配向が生ずるため、補償用粒体が含有されないときは配向複屈折性が発現されるようになるが、補償用粒体が混入されていることにより、得られる延伸フィルムは低複屈折性のものとなる。
【００５７】
すなわち、以上のようにして得られる成形された光学樹脂材料や延伸処理された光学樹脂材料は、複屈折性がきわめて低いものであり、その程度は、補償用粒体の含有割合や配向の程度、その他の条件によって異なるが、事実上複屈折性を示さない非複屈折性の場合もある。
また、高分子樹脂中に補償用粒体が存在することにより、当該高分子樹脂の流動性が高くなる場合があり、この場合には、成形加工や延伸処理における高分子樹脂のポリマー鎖の配向が抑制されるために、結果として、当該高分子樹脂の配向複屈折性が抑制される効果が得られ、これによっても、光学樹脂材料は低複屈折性のものとなる。
なお、この明細書において、単に「低複屈折性」というときは、非複屈折性である場合が包含されるものとする。
【００５８】
以上のような本発明による光学樹脂材料は、上記の特性を活かして、各種の光学部品の材料として利用することができ、これらの光学部品は各種の光学機器に利用することができる。
具体的に説明すると、本発明による光学樹脂材料は、特に液晶素子用の部材として高い有用性を有する。その具体例は、例えば液晶層と偏光板との間に介在するよう配置される液晶素子用基板である。すなわち、本発明による光学樹脂材料によって形成された基板は、複屈折性がなくあるいは複屈折性が小さいために十分に液晶素子用基板として用いることができ、従来から使用されているガラス系基板と比較したとき、光学樹脂材料であることの利点が有効に活用され、良好な性能を有する液晶デバイスを有利に提供することができる。
【００５９】
また液晶素子用の偏光板は、偏光子の両面に透明樹脂シートを接合させて形成されるが、この透明樹脂シートとして、本発明による光学樹脂材料よりなるシートを用いることができ、液晶素子用基板の場合と同様に、良好な性能を有する液晶デバイスを有利に提供することができる。
【００６０】
更に、液晶素子を形成する各構成要素を接着させるための接着剤として、本発明による光学樹脂材料を用いることができる。このような接着剤は、それ自体が低複屈折性であることにより、また構成要素の材料の選択において大きな自由度が得られる点で、好ましいものである。すなわち、従来においては、低複屈折性の樹脂よりなる接着剤が提供されていないため、例えばモノクロタイプのように或る程度の複屈折性が許容される場合を除いて、各構成要素の接合が粘着剤によって行われているが、この粘着剤に代わるものとして本発明による光学樹脂材料よりなる接着剤を用いることができ、これにより、耐久性や耐熱性などの点で液晶素子の性能を向上させることができる。
【００６１】
図３は、液晶素子の構成の一例を示す説明用断面図である。この例において、１０は液晶層、１１ａ、１１ｂは液晶層の上下に配置された基板、１２ａ、１２ｂはそれぞれ基板１１ａ、１１ｂの外面上に配置された偏光板であって、偏光板１２ａ、１２ｂの各々は、偏光子１３の両面に透明樹脂シート１４が接合されて構成されている。
このような構成の液晶素子においては、基板１１ａ、１１ｂおよび透明樹脂シート１４を本発明による光学樹脂材料によって形成することができ、また、基板１１ａ、１１ｂと各偏光板ｌ２ａ、１２ｂとの接合のために、本発明による光学樹脂材料を原材料とする接着剤を用いることができる。
【００６２】
図４は、液晶素子の他の構成例を示す説明用断面図である。この例において、１０は液晶層、１５ａ、１５ｂは液晶層の上下に配置された基板であり、偏光板１６ａ、１６ｂは、それぞれ、当該基板１５ａ、１５ｂと、その外面上に配置された偏光子１３と、この偏光子１３の外面上に接合された透明樹脂シート１４とが積層された構成とされている。すなわち、各基板１５ａ、１５ｂが、図３の構成における液晶層１０側の透明樹脂シート１４を兼ねた構成であり、各偏光板１６ａ、１６ｂが各基板１５ａ、１５ｂと一体化されている。
このような構成の液晶素子においても、基板１５ａ、１５ｂおよび透明樹脂シート１４を本発明による光学樹脂材料によって形成することができ、また、接合のために、本発明による光学樹脂材料を原材料とする接着剤を用いることができる。
【００６３】
また、既述の一般式（１）に示すノルボルネン誘導体より得られる開環重合体またはその水素添加重合体を高分子樹脂として用い、これに補償用粒体を混入したものは、高い透明性と優れた耐熱性を有し、しかも低複屈折性を有する光学樹脂材料であり、特に光ディスクの製造に有利である。
【００６４】
【実施例】
以下、本発明の実施例を説明するが、本発明はこれによって限定されるものではない。
＜実施例１＞
この実施例においては、高分子樹脂として、メチルメタクリレートとベンジルメタクリレートとをモル比で７８：２２の割合で共重合させて得られる、屈折率が１．５２の共重合体を用い、補償用粒体として、屈折率が１．４９のアダマンタンよりなる最大粒径が１００ｎｍの粒体を用いた。このアダマンタンは、分極に関して等方性を有する低分子量物質である。
そして、上記の高分子樹脂を加熱溶融させ、これに、当該高分子樹脂に対する割合が５重量％となる量の補償用粒体を添加して十分に混練することにより、光学樹脂材料を調製し、これを押し出し成形することにより、厚さが１００μｍののフィルムを製造した。これを「試料１」とする。
【００６５】
この試料１のフィルムに対して、延伸温度８０℃、延伸速度４ｍｍ／ｍｉｎ、延伸倍率３．５倍の条件で１軸延伸処理を施し、得られた延伸フィルムの複屈折値Δｎを求めたところ、−３．１１×１０^-6であった。
また、試料１のフィルムに対して、延伸処理の条件を種々に変更して１軸延伸処理を施し、得られた延伸フィルムの複屈折値Δｎを求めた。結果は表１に示すとおりである。
【００６６】
一方、補償用粒体を添加せずに高分子樹脂をそのまま用いた他は、試料１と同様にして参照用フィルムを製造した。これを「参照試料１」とする。
この参照試料１のフィルムに対して、延伸温度９０℃、延伸速度４ｍｍ／ｍｉｎ、延伸倍率３．０倍の条件で１軸延伸処理を施し、得られた延伸フィルムの複屈折値Δｎを求めたところ、１．２３×１０^-5であった。
また、試料１のフィルムに対して、延伸処理の条件を変更して１軸延伸処理を施し、得られた延伸フィルムの複屈折値Δｎを求めた。結果は表１に示すとおりである。
【００６７】
【表１】

【００６８】
表１の結果から、先ず、試料１の場合も、また参照試料１の場合も、延伸処理条件が異なれば、得られるフィルムの複屈折値Δｎが異なることから、延伸処理によって配向複屈折性が発現していることが理解される。
そして、高分子樹脂中に補償用粒体が含有されていない参照試料１の場合にはいずれの延伸処理条件においても複屈折値Δｎは正であるのに対し、補償用粒体が含有された場合には、フィルム全体の複屈折値Δｎが負となっており、このことから、適当な条件で延伸処理を行なうことにより、複屈折性が変化して低複屈折性の光学樹脂材料が得られることが理解される。
これは、延伸処理の程度によって、高分子樹脂のポリマー鎖の配向の程度が異なり、その結果、当該高分子樹脂の配向複屈折性および補償用粒体による分布複屈折性の程度がそれぞれ変化し、後者によって補償された後のフィルム全体の複屈折性が異なったものとなるからであると考えられる。
以上のことから、透明性を有する高分子樹脂に、適当な屈折率の粒体を補償用粒体として適宜の割合で混入することにより、低複屈折性の光学樹脂材料が得られることが明らかである。
【００６９】
＜実施例２＞
下記の構造式（１）で示される８−メチル−８−カルボキシメチルテトラシクロ［4.4.0.1^2,5.1^7,10］−３−ドデセンの２５０重量部と、１−ヘキセン４１部と、トルエン７５０重量部とを、窒素ガスで置換した反応容器内に仕込み、６０℃に加熱した。これに、トリエチルアルミニウム（１．５モル／ｌ）のトルエン溶液０．６２重量部と、ｔ−ブタノール／メタノールで変性した六塩化タングステン溶液（濃度０．０５モル／ｌ、ｔ−ブタノール：メタノール：タングステン＝０．３５：０．３：１）３．７重量部を触媒として加え、８０℃で３時間加熱攪拌することにより、開環重合体溶液（ａ）を得た。
この重合反応における重合転化率は９７％であった。また、得られた重合体の固有粘度（η_inh ）は０．４５ｄｌ／ｇ (クロロホルム中、３０℃、濃度０．５ｇ／ｄｌ）であった。
【００７０】
【化２】

【００７１】
このようにして得られた開環重合体溶液（ａ）の４０００重量部をオートクレーブに入れ、これに水素添加触媒を加え、水素ガス圧１００ｋｇ／ｃｍ² 、反応温度１６５℃の条件で３時間加熱して水素添加を行った。
こうして得られた水素添加重合体を大量のメタノール中に注いで重合体を凝固させた。ここに得られた水素添加重合体の水素添加率は実質上１００モル％であった。
【００７２】
上記の水素添加重合体のトルエン溶液に、平均粒子径が約７ｎｍで実質的に球形のシリカ微粉末「アエロジル３００」（日本アエロジル（株）製）を、重合体に対して０．１重量％の割合で添加して、シリカ分散溶液を調製した。
このシリカ分散溶液を用い、溶液キャスト法により乾燥後の厚さが１００μｍのフィルムを作製した。これを試料２とする。
この試料２のフィルムに対して、延伸温度１７０℃、延伸速度８ｍｍ／ｍｉｎ、延伸倍率３．０倍の条件で延伸処理を行なった。そして、得られた延伸フィルムの複屈折値Δｎを求めたところ、１．３２×１０^-3であった。
一方、シリカ微粉末を添加しない溶液を用いたほかは、上記と同様にしてフィルムを作製し、これを参照試料２として同様の延伸処理を行ない、得られた延伸フィルムの複屈折値Δｎを求めたところ、１．９２×１０^-3であった。
このことから、試料２に係る延伸フィルムでは、シリカ微粉末が存在していることにより、複屈折性が低減化されていることが明らかである。
【００７３】
【発明の効果】
本発明によれば、マトリックスを構成する高分子樹脂が、それ単独では複屈折性を示すものであっても、特定の条件を具えた複屈折性補償用粒体が混入されて分布していることによって生じる分布複屈折性により、高分子樹脂の有する複屈折性が補償され、複屈折性が低減化された光学樹脂材料が得られる。
特に、高分子樹脂のポリマー鎖が配向されている場合において、複屈折性補償用粒体の分布が、当該高分子樹脂体のポリマー鎖の配向方向に疎で当該配向方向と交差する方向に密である分布であることにより、高分子樹脂における配向複屈折性が、複屈折性補償用粒体によって生じる分布複屈折性により補償され、従って確実に低複屈折性が得られる。
【００７４】
そして、高分子樹脂は基本的に制約を受けることなく、従ってそれ自体の複屈折性の符号が正であっても負であっても、確実に低複屈折性の光学樹脂材料を提供することができる。また、その結果、高分子樹脂を、広い範囲のものから自由に選択することができるので、目的とする用途に応じて好適な特性を有する高分子樹脂を用いて低複屈折性の光学樹脂材料を得ることができ、従って、例えば優れた光学特性、機械的特性、あるいは特に高い耐熱性を有する低複屈折性の光学樹脂材料を有利に提供することが可能となる。
【００７５】
また、本発明の低複屈折性光学樹脂材料を用いることにより、低複屈折性の各種の光学部品を形成することができ、複屈折性が影響する光学要素を含む機器、例えば液晶デバイスの構成要素を有利に提供することができ、また各種性能を向上させることが可能となる。
【図面の簡単な説明】
【図１】高分子樹脂の配向されたポリマー鎖の状態と、発現される複屈折性についての説明図である。
【図２】屈折率楕円体についての説明図である。
【図３】液晶素子の構成の一例を示す説明用断面図である。
【図４】液晶素子の他の構成例を示す説明用断面図である。
【符号の説明】
１ 結合単位
２ 楕円マーク
３ 屈折率楕円体
１０ 液晶層
１１ａ、１１ｂ 基板
１２ａ、１２ｂ 偏光板
１３ 偏光子
１４ 透明樹脂シート
１５ａ、１５ｂ 基板
１６ａ、１６ｂ 偏光板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical resin material having a low birefringence, and more specifically, the birefringence is reduced so that the birefringence is not substantially exhibited, or the birefringence is low, but the degree is low The present invention relates to a manufacturing method and its application.
[0002]
[Prior art]
In general, in an optical resin material, birefringence is generated according to the actual processing method, as is widely known including its cause. That is, in almost all of the polymer resins usually used as optical resin materials, the monomers forming the polymer have optical anisotropy due to the refractive index. Anisotropy is manifested in an optical resin material made of a polymer arranged or oriented in a certain direction, resulting in birefringence.
[0003]
Specifically, the polymer resin as it is produced by the polymerization reaction does not exhibit birefringence. This is because the polymer chains are randomly entangled and the polymer chains are not oriented. That is, in this state, since the optical anisotropy of each monomer cancels each other, birefringence is not expressed as a polymer resin.
However, when such a polymer resin undergoes a molding process such as injection molding or extrusion molding, the resulting polymer resin is oriented as a result of orientation of random polymer chains due to external forces applied at that time. It exhibits birefringence.
[0004]
FIG. 1 is an explanatory diagram of the state of the polymer chain in which the polymer resin is oriented and the birefringence exhibited thereby. As shown in this figure, the polymer resin that has undergone the molding step is usually in a state in which a large number of bond units 1 that form the polymer chain are volume-bound along a specific orientation direction. Here, the bond unit is a unit of one molecule of monomer, and is represented by a rectangular figure in the figure, and the orientation direction is the left-right direction of the figure.
As described above, in almost all polymer resins used as the optical resin material, each bonding unit 1 has optical anisotropy with respect to the refractive index. That is, the refractive index n regarding the polarization component in the direction parallel to the orientation direction_prAnd the refractive index n related to the polarization component in the direction perpendicular to the orientation direction (vertical direction in the figure)_vtIs in a different state.
[0005]
Such optical anisotropy can be expressed by a refractive index ellipsoid as well known. In FIG. 1, the ellipse mark 2 written in each coupling unit 1 follows the notation system.
For example, in the case of polymethyl methacrylate (PMMA), a bonding unit [—CH₂-C (CH_Three) (COOCH_Three)-] Has a relatively small refractive index in the alignment direction and relatively large in the direction perpendicular to the alignment direction._pr<N_vtTherefore, as shown in FIG. 2, the refractive index ellipsoid 3 when viewed on a macro scale is a vertically long one.
Thus, the refractive index n regarding the polarization component in the direction parallel to the alignment direction_prAnd the refractive index n related to the polarization component in the direction perpendicular to the orientation direction._vtIs the difference Δn (= n_pr-N_vt) Is called the birefringence value.
[0006]
The birefringence value Δn of a typical polymer resin used as an optical resin material is −0.100 for polystyrene, −0.0043 for polymethyl methacrylate, +0.210 for polyphenylene oxide, +0.106 for polycarbonate, and polyvinyl chloride. Is 0.027, polyethylene terephthalate is +0.105, and polyethylene is +0.044.
In this specification, the birefringence resulting from the orientation of the polymer chain is referred to as orientation birefringence. When the birefringence value Δn has a positive sign (Δn> 0), the birefringence sign is positive. The sign of the refraction value Δn being negative (Δn <0) is expressed as “the sign of birefringence is negative”.
[0007]
Such orientation birefringence is a major problem when polarization characteristics are involved in the application or application of optical resin materials. A typical example is an optical component in, for example, a write / erase type magneto-optical disk apparatus. In this write / erase type magneto-optical disk apparatus, a polarized beam is used as a read beam or a write beam. If the optical element disposed in the optical path, for example, the disk itself or the lens exhibits birefringence, the reading or writing accuracy is adversely affected.
[0008]
In addition, there is a liquid crystal element in which the birefringence in the optical element used has an important influence. This liquid crystal element has a structure in which transmission / non-transmission of light is controlled by rotating a polarization plane of polarized light by a liquid crystal layer between a polarizer having a crossed Nicol or a parallel Nicol and an analyzer. Therefore, in the liquid crystal element, the birefringence of each of the constituent elements becomes a big problem. For this reason, the selection range of the optical resin material used as the material of the constituent elements of the liquid crystal element is narrow and extremely limited.
[0009]
Conventionally, various contrivances for reducing the orientation birefringence in the optical resin material have been made, and a representative one is disclosed in International Publication No. WO96 / 06370. This technology adds a low-molecular substance that can be aligned in the same direction as the alignment direction of the bond chain to the matrix made of a transparent polymer resin when the polymer chain of the polymer resin in the matrix is aligned by external force. The birefringence of the low molecular weight material counteracts the orientation birefringence of the polymer resin.
[0010]
Specifically, in this technique, the polymer resin forming the matrix has an orientation birefringence having a positive or negative sign, but the low molecular weight substance added thereto is a polymer resin. The birefringence having a sign opposite to that of the orientation birefringence in FIG. 2 is obtained, and the low birefringence optical resin material is obtained by utilizing the birefringence of the two being offset.
In other words, in this optical resin material, the polymer chain undergoes orientation when subjected to an action such as stress from the outside in a process such as molding, and at that time, the added low-molecular substance is also oriented to the polymer chain. The major axis direction of the refractive index ellipsoid in the low molecular weight substance that is oriented in accordance with the orientation of the polymer chain is perpendicular to the major axis direction of the refractive index ellipsoid in the polymer resin. By utilizing this, the birefringence of the polymer resin is reduced in an offset manner, and the low birefringence is realized as a whole.
[0011]
Such technology has many advantages. For example, by adjusting the addition amount of the latter with respect to the former according to the types of the high molecular resin and the low molecular substance to be combined, one having an overall birefringence close to zero can be obtained. Moreover, in principle, this technology can be applied to any polymer resin, and a low-molecular substance does not substantially participate in the polymerization reaction of the matrix polymer resin. Since there is no reactivity with the monomer that gives the resin, there are relatively few restrictions on the combination of the polymer resin and the low-molecular substance, and thus a relatively large degree of freedom in selecting the polymer resin for the optical resin material. It is done.
Furthermore, a low molecular weight substance generally has a larger optical anisotropy with respect to the refractive index than each unit molecule forming a polymer resin, and therefore, a desired effect can be achieved with a relatively small addition amount. Therefore, the characteristics of the matrix polymer resin can be effectively utilized in the optical resin material.
[0012]
However, in the technique of reducing the birefringence of the optical resin material by adding a low molecular substance, for example, the low molecular substance to be added is naturally in the selection range in relation to the polymer resin for the matrix. There is a limit.
A particularly important problem is that it is actually difficult to obtain a low molecular weight substance exhibiting negative orientation birefringence. That is, among polymer resins widely used as optical resin materials, this applies to polymer resins having a positive birefringence, in addition to polymethyl methacrylate and polystyrene having a negative birefringence. The range of low molecular weight materials that have negative birefringence to be made is narrow, and this method may not be applicable in practice. Specific examples of the polymer resin having a positive birefringence include polyethylene (Δn: +0.044) and norbornene-based resin (Δn: eg +0.0192).
[0013]
[Problems to be solved by the invention]
The present invention has been made in the background as described above, and is an optical resin material made of a polymer resin. The polymer resin can be duplicated without sacrificing the properties of the polymer resin. An object of the present invention is to provide a low-birefringence optical resin material and a method for producing the same, in which the refractive index is reliably reduced regardless of the sign.
Another object of the present invention is to provide various useful optical parts and other articles or materials by applying the above low birefringence optical resin material.
[0014]
[Means for Solving the Problems]
  The low birefringence optical resin material of the present invention is a polymer resin having transparency mixed with birefringence compensation particles having a size smaller than the wavelength of light. , Particles made of a material having isotropic properties with respect to polarization, or particles having isotropic properties with respect to shapeAnd
  The polymer resinThe polymer chain is oriented by external force, and the distribution of the birefringence compensating particles in the polymer resin body is sparse in the polymer chain orientation direction of the polymer resin body and intersects the orientation direction The birefringence in the polymer resin is compensated by the distributed birefringence generated by the birefringence compensating particles.It is characterized by that.
  In the above, the polymer resin can be a ring-opening polymer of a norbornene derivative, and the birefringence compensating granules can be granules made of adamantane or spherical silica.
[0015]
  The method for producing the low birefringence optical resin material of the present invention includes:Birefringence compensation granulesIt can be set as the method which has the process of extending | stretching the high molecular resin which has transparency mixed.
[0016]
The optical component of the present invention is characterized by comprising the above-mentioned low birefringence optical resin material.
An optical apparatus according to the present invention is characterized by using the above optical component as an optical element.
The adhesive for optical parts of the present invention is made of the above-mentioned low birefringence optical resin material, and is used for joining optical parts or optical elements.
[0017]
The substrate for a liquid crystal element of the present invention is made of the above low birefringence optical resin material, and is interposed between the liquid crystal layer and the polarizing plate in the liquid crystal element.
The polarizing plate for a liquid crystal element of the present invention is characterized in that a sheet made of the above low birefringence optical resin material is bonded to both surfaces of a polarizer for a liquid crystal element.
The adhesive for liquid crystal elements of the present invention is made of the above-mentioned low birefringence optical resin material, and is used for joining elements that form liquid crystal elements.
The optical disk of the present invention is characterized in that it is composed of the above-mentioned low birefringence optical resin material, in which the polymer resin is a ring-opening polymer of a norbornene derivative.
[0018]
[Action]
According to the above configuration, even if the polymer resin constituting the matrix is birefringent by itself, particles for birefringence compensation having specific conditions are mixed and distributed. The birefringence of the polymer resin is compensated by the distributed birefringence generated by the optical resin material, thereby obtaining an optical resin material with reduced birefringence.
In particular, when the polymer chain of the polymer resin is oriented, the distribution of the birefringence compensating granules is sparse in the polymer chain orientation direction of the polymer resin body and dense in the direction intersecting the orientation direction. The distribution birefringence in the polymer resin is compensated by the distribution birefringence generated by the birefringence compensating particles.
And since the said optical resin material is low birefringence, favorable performance is obtained by forming various optical components and optical products.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The low birefringence optical resin material of the present invention is obtained by mixing a birefringence compensating granule (hereinafter simply referred to as “compensation granule”) in a polymer resin having transparency. .
In the present invention, the polymer resin constituting the matrix of the optical resin material basically has transparency necessary for the intended use as the optical resin material and has other necessary characteristics. As long as it is not particularly limited, any polymer resin may be used.
On the other hand, the compensation particles mixed in the polymer resin are required to have a size smaller than the wavelength of the applied light, and are made of a material having an isotropic property with respect to polarization. Or a granule that is isotropic in terms of shape.
[0020]
In one embodiment of the low birefringence optical resin material of the present invention, the polymer resin constituting the matrix is in a state in which the polymer chain is oriented in a specific direction. The distribution is sparse in the orientation direction of the polymer chain in the resin and dense in the direction intersecting the orientation direction, and is present in the polymer resin.
Here, the state in which the polymer chain is oriented in a specific direction in the polymer resin is usually caused by an external force acting in a specific direction in a process such as molding or stretching treatment. The cause of orientation or the reason for orienting the polymer chain is not limited.
In another aspect of the present invention, the polymer resin constituting the matrix does not have a specific orientation direction, and the compensation particles are simply present in a uniform distribution in the polymer resin. May be. In this case, for example, the orientation birefringence generated when the orientation state is obtained by a subsequent treatment is reduced.
[0021]
In the optical resin material of the above aspect, when the compensation particles are present in a specific state in the polymer resin in which the polymer chain is in an oriented state, such a compensation particle does not exist. In comparison, the birefringence is reduced. This is because, for the following reasons, the orientation birefringence expressed in the resin material composed solely of the polymer resin is compensated by the distributed birefringence generated by the compensating particles.
[0022]
That is, in a system of a certain substance, an optical phenomenon called structural birefringence occurs when a specific condition regarding the structure is satisfied. One of the structural birefringence is a phenomenon called distributed birefringence. . The present invention utilizes this.
More specifically, distributed birefringence is a dispersion of particles in a transparent medium in which particles having a refractive index different from that of the medium and having a size smaller than the wavelength of light are dispersed. Is a phenomenon that exhibits inherent birefringence as a dispersion system by taking a non-uniform dispersion state.
[0023]
It is already known that such a phenomenon of distributed birefringence itself exists, and for example, there are the following reports.
(1) M. Born and E. Wolf, “Prinsiples of Optics”
(2) T. Takamori and M. Tomozawa, “Treatise on materials science and technology”, 12, Glass 1. 123, Academic Press, New York (1977)
(3) Ce-Wen Nan and D.M.Smith, “A new theoretical description for anomalous birefringence of phase-separated glasses”, J. Non-Crystalline Solids, 130 293 (1991)
[0024]
For example, in the above-mentioned document (2), the following formula 1 is proposed as a formula representing distributed birefringence when the dispersed particles are spherical and isotropic with respect to polarization. Where n_eIs the refractive index in the direction in which the particle distribution is sparse, n_oIs the refractive index in the direction of dense particle distribution, n₁Is the refractive index of the particle, n₂Is the refractive index of the medium, f is the volume fraction of the dispersed particles, and L_eIs the depolarization coefficient in the direction of dense particle distribution, L_oIs the depolarization coefficient in the direction in which the particle distribution is sparse.
[0025]
[Expression 1]

[0026]
Reference (3) is based on the scattering theory and the effective medium theory. The following formula 2 represents the distributed birefringence in the spherical particles, and the following formula for N (r ′) in the formula 2 Equation 3 is proposed.
In each equation, r is the radius of the particle, v is the volume fraction of the dispersed particle, and n_hIs the refractive index in the direction in which the particle distribution is sparse or the refractive index in the direction in which the particle distribution is dense, n₁Is the refractive index of the particle, n₂Is the refractive index of the medium, L_hIs the repolarization coefficient in the direction in which the particle distribution is dense or depolarization coefficient in the direction in which the particle distribution is sparse, and δ is the dispersion.
[0027]
[Expression 2]

[0028]
The depolarization coefficient in each of the above equations substantially corresponds to the distance between the dispersed particles, and therefore corresponds to the density of the dispersed particles. Here, it can be said that the expressions 1 and 2 mean substantially the same except that the latter is more precise. Therefore, using the simpler expression 1, the term (n on the left side) that gives the distributed birefringence value in expression 1 will be described._e ²-N_o ²) Is the right-hand side term (L_e-L_o), In other words, the depolarization factor L in the direction in which the particle distribution becomes dense._eAnd the repolarization coefficient L in the direction in which the particle distribution is sparse₀It can be seen that it is determined by the size relationship. That is, the distributed birefringence is determined regardless of the magnitude relationship between the refractive index of the medium and the refractive index of the dispersed particles, and the refractive index in the direction in which the particle distribution is dense becomes sparse. It occurs to be larger than the refractive index in the direction.
[0029]
As is clear from Equation 1, the refractive index n of the medium₂And the refractive index n of the particles₁The larger the difference between the two, the larger the distributed birefringence value.
On the other hand, from Formula 2, it is derived that the distribution birefringence value increases as the size of the granule (radius r) increases.
However, the depolarization factor (L_eAnd L_o), That is, the anisotropy of the refractive index due to the distribution is also related to the polarization anisotropy of the particles themselves. For example, if the particles are elliptical, depending on their shape, if they have polarization anisotropy that increases the refractive index in the major axis direction rather than the minor axis direction, this is distributed birefringence. Will be affected. That is, when an external force or the like is applied to a medium in which particles are uniformly dispersed to generate a dense distribution in the particles, in general, particles having shape anisotropy have a distribution of the particles. The major axis direction becomes parallel to the sparse direction. Therefore, a relatively large refractive index in the major axis direction is a dense direction of particle distribution (a direction perpendicular to the major axis direction). ) To cancel out the large refractive index.
[0030]
That is, generally, if there is polarization anisotropy (birefringence) accompanied by shape anisotropy in a granular material, this will suppress the expression of distributed birefringence. Therefore, in order to effectively exhibit distributed birefringence, it is desirable that the particles have isotropic properties with respect to polarization, or have isotropic properties with respect to shape.
As is understood from the above description, the shape isotropy in this case is a regularity that causes the polarization anisotropy as a whole if the grains have anisotropy with respect to the polarization. It means that the shape is isotropic to the extent that no orientation occurs. Typical examples of such isotropic shapes are spherical and regular polygons.
[0031]
Thus, the optical resin material of the present invention is a polymer resin in which the compensation particles are uniformly mixed and dispersed, and an external force or the like is applied to the polymer resin in which the particles are mixed. When orientation occurs in the chain, the compensation particles are also affected by the orientation movement of the polymer chain, and the distribution inevitably changes in the distribution, and as a result of this distribution change, the compensation granule is aligned with the orientation of the polymer chain. Therefore, the distribution birefringence exhibited by this is always negative with respect to the orientation direction of the polymer chain.
[0032]
In order to develop a compensating birefringence that reduces the distribution birefringence of such a polymer resin, as is apparent from the above description,
(1) The size of the particles for compensation is smaller than the wavelength of light, that is, the particles for compensation are of a size that does not cause scattering that substantially reduces the transparency of the polymer resin. , And
(2) It is a granule made of a material having isotropicity with respect to polarization, or a granule having isotropicity with respect to shape,
is required.
[0033]
The wavelength of light related to the size of the compensation particles need only be considered on the basis of the wavelength of light applied to an optical device in which the obtained optical resin material is used, and visible light or light in the vicinity thereof is used. In some cases, the size of the compensation granules needs to be several hundred nanometers or less.
In practice, granules of such a size level are relatively easy to obtain. Further, it is possible to easily obtain a granule having isotropicity with respect to polarization and a granule having isotropic property with respect to the shape.
Moreover, such a granule can be applied as a compensation granule to virtually any polymer resin, and thus the degree of freedom in selecting the polymer resin used in the optical resin material of the present invention. Is extremely large. In addition, such particles do not substantially affect the optical properties other than the birefringence of the polymer resin, and have little influence on the mechanical properties.
[0034]
As understood from the above description, the present invention reduces the orientation birefringence expressed in the polymer resin by adding a certain substance in the polymer resin constituting the matrix, or In terms of compensation, the mechanism is the same as that of the prior art, but the mechanism for developing the birefringence for reducing the orientation birefringence of such a polymer resin is completely different. In other words, in the prior art, the low-molecular substance added exhibits a birefringence having a sign opposite to the orientation birefringence in the polymer resin, and as a whole, the low-compound In order to achieve refraction or low anisotropy, the present invention uses distributed birefringence, which is a type of structural birefringence.
[0035]
In the present invention, the polymer resin for constituting the matrix is required to have a certain degree of transparency for use as an optical resin material. There is no particular restriction due to the relationship with the compensation particles mixed in the resin, and therefore the degree of freedom in selecting the polymer resin is extremely large. Actually, it is preferable to use a polymer resin having general aptitude as an optical resin material, and particularly has suitable characteristics according to a specific application, such as excellent heat resistance and mechanical strength. It is preferable to use one.
The degree of transparency required for the polymer resin is determined by the intended use of the optical component or the required optical characteristics, and is not particularly limited. The polymer resin may have a positive or negative birefringence sign.
[0036]
Specific examples of the polymer resin used in the present invention include polyolefins such as polyethylene and polypropylene, aromatic vinyl polymers such as polystyrene, poly (meth) acrylates such as polymethyl methacrylate, polyphenylene oxide, and polycarbonates. , Polyvinyl chloride, polyethylene terephthalate, polyarylate, polyether sulfone, polyethylene naphthalate, polymethylpentene-1, alicyclic polyolefins (for example, ring opening of cyclic olefins such as dicyclopentadiene polyolefin and norbornene polyolefin) (Co) polymers, hydrogenated (co) polymers thereof, saturated copolymers of cyclic olefins and unsaturated double bond-containing compounds), such as tricyclodecanyl methacrylate, Copolymers of alicyclic (meth) acrylates such as rohexyl methacrylate and isobornyl methacrylate and (meth) acrylic acid esters such as methyl methacrylate, polysulfone, polyetherimide, amorphous polyamide, polyphenylene ether, and cyclic Mention may be made of hydrogenated polymers of cationic (co) polymers of olefins, cyclopentadiene, aromatic vinyl compounds and others.
Among these, examples of preferable optical characteristics include polymethyl methacrylate, certain types of polycarbonates, and alicyclic polyolefin-based polymers.
[0037]
Of the above polymer resins, a polymer having a high degree of orientation birefringence alone needs to add a large amount of particles for compensation, and as a result, the transparency of the resulting optical resin material decreases. There is a case.
However, since the alicyclic polyolefin-based polymer is usually a polymer exhibiting a small positive birefringence, the amount of compensation particles to be mixed may be small, and therefore, high transparency and heat resistance can be achieved. In addition, an optical resin material having low birefringence can be obtained, which is extremely preferable.
[0038]
Preferred examples of the alicyclic polyolefin-based polymer include ring-opening polymerization obtained by ring-opening polymerization of a monomer comprising a norbornene derivative represented by the following general formula (1) or a copolymerizable monomer copolymerizable therewith. A polymer or a hydrogenated polymer obtained by further hydrogenating such a ring-opening polymer can be mentioned. Such a ring-opening polymerization reaction of the monomer is usually performed by a metathesis polymerization catalyst.
[0039]
[Chemical 1]

[Wherein, A and B are a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, X and Y are a hydrogen atom or a monovalent organic group, and m is 0 or 1. ]
[0040]
Among the monomers having such a norbornene ring, X or Y in the general formula (1) is represented by the formula — (CH₂)_nCOOR¹Is preferable in that the resulting ring-opening polymer has a high glass transition temperature and a low hygroscopicity. It is preferable that one polar substituent composed of the carboxylic acid ester group is contained per molecule of the monomer because the resulting ring-opening polymer has low hygroscopicity.
[0041]
And the formula-(CH₂)_nCOOR¹Among the carboxylic acid ester groups represented by the formula (1), the smaller the value of n, the higher the glass transition temperature of the resulting ring-opening polymer, and the more preferable the monomer having n of 0 is easy to synthesize. Moreover, it is preferable at the point from which a favorable characteristic is acquired by the ring-opening polymer obtained.
In the above formula, R¹Is a hydrocarbon group having 1 to 20 carbon atoms, and is preferable in that the hygroscopicity of the polymer obtained decreases as the carbon number increases. However, from the viewpoint of the balance with the glass transition temperature of the polymer obtained, it is preferably a chain alkyl group having 1 to 4 carbon atoms or a (poly) cyclic alkyl group having 5 or more carbon atoms, particularly a methyl group. It is preferable that
Furthermore, a monomer in which a hydrocarbon group having 1 to 10 carbon atoms is simultaneously bonded as a substituent to a carbon atom to which a carboxylic acid ester group is bonded has a hygroscopic property without lowering the glass transition temperature of the resulting polymer. Since it reduces, it is preferable. In particular, a monomer in which the substituent is a methyl group is preferable in terms of easy synthesis.
Among the above monomers, a tetracyclododecene derivative in which m is 1 in the general formula (1) is preferable in that a polymer having a high glass transition point is obtained.
[0042]
Among the compounds represented by the general formula (1), examples of preferable compounds include 8-carboxymethyltetracyclo [4.4.0.1^2,5.1^7,10] -3-dodecene, 8-methyl-8-carboxymethyltetracyclo [4.4.0.1^2,5.1^7,10] -3-dodecene, 5-carboxymethyl-bicyclo [2.2.1] -2-heptene, and the like.
[0043]
The above monomer can be ring-opening copolymerized with a monomer copolymerizable therewith, and such a copolymer can also be used.
When the above ring-opening polymer is hydrogenated, the hydrogenation rate is preferably high, preferably at least 90 mol% or more, and particularly substantially 100 mol%.
The molecular weight of the ring-opening polymer or the hydrogenated polymer is preferably 20,000 to 500,000 in terms of weight average molecular weight in terms of polystyrene.
[0044]
In the present invention, the compensating particles can be freely selected from a wide range of materials as long as they satisfy the above conditions.
As described above, the size of the compensation particles may be smaller than the wavelength of light applied to the optical component or optical element made of the optical resin material. For example, when the light is visible light The size may be several hundred nanometers or less, for example, about 50 to 300 nm. Further, when the applied light is laser light, a compensation particle having a size corresponding to the wavelength may be used. When the size of the compensation granules is excessive, the resulting optical resin material has reduced transparency due to the presence of the compensation granules.
[0045]
In addition, the compensation particles are made of a material having isotropic property with respect to polarization, or when the particles are made of a material having no isotropic property with respect to polarization, the particles may have isotropic properties with respect to the shape. is necessary.
Specific examples of the substance having isotropic property regarding polarization include isotropic organic compounds such as adamantane and dendrimer.
[0046]
On the other hand, a particle having an isotropic shape typically has an isotropic shape such as a spherical shape or a regular polygon, but has a substantially isotropic shape. What is necessary is just to be a thing, and the ratio should just have the ratio of the minor axis with respect to the major axis to 1/10 or more.
Specific examples of such granular materials include silica, aluminum oxide, titanium oxide, iron oxide, cerium oxide, yttrium oxide, manganese oxide, zirconium oxide, cobalt blue, indium oxide, magnesium oxide, neodymium oxide, and oxide. Examples thereof include particles of inorganic compounds such as holmium, copper oxide, and a composite oxide of aluminum oxide and magnesium oxide.
These inorganic compounds can be made into a granule having a size smaller than the wavelength of light, and a granule having an isotropic shape can be obtained.
[0047]
The mixing ratio of the compensation particles to the polymer resin is not particularly limited as long as it is a ratio effective for reducing the orientation birefringence of the polymer resin. 0.001 to 20% by weight, for example, 0.01 to 10% by weight. The mixing ratio of the compensation particles is preferably small if the desired effect is obtained. When the mixing ratio of the compensation particles is increased, the transparency, mechanical strength, and heat resistance of the resulting optical resin material are increased. Intrinsic properties of the polymer resin such as property may be deteriorated.
[0048]
In order to produce the low birefringence optical resin material of the present invention, a monomer or a composition for producing a transparent polymer resin by a polymerization reaction is prepared, and before the polymerization reaction of the polymerizable material is started. In this stage, the compensation particles are mixed and sufficiently dispersed, and after adding an appropriate polymerization initiator, chain transfer agent, etc., the polymerization reaction is started by supplying energy such as heating or ultraviolet irradiation. It is possible to adopt a method of proceeding and thereby obtaining an optical resin material.
[0049]
Here, the kind and amount of the polymerization initiator and chain transfer agent may be selected according to the same criteria as in the case of a normal polymerization reaction. For example, in the case of thermal polymerization, a peroxide such as benzoyl peroxide can be used as a thermal polymerization initiator. In the case of ultraviolet irradiation, benzoin methyl ether, which is an ultraviolet radical polymerization initiator, can be used. As the chain transfer agent, normal butyl mercaptan or the like can be used in any case.
This production method is advantageous in that a polymer resin mixed with compensation particles can be produced directly upon completion of the polymerization reaction.
[0050]
In addition, after the start of the polymerization reaction of the monomer that forms the polymer resin or the composition thereof and before the completion of the polymerization reaction, that is, in a state where the polymerization reaction is performed to some extent and a polymerizable oligomer exists. It may be a method in which the compensation granules are mixed and sufficiently dispersed, and then the polymerization reaction is completed.
Also in this manufacturing method, the polymer resin mixed with the compensation particles can be directly manufactured by completing the polymerization reaction.
[0051]
In the above method, it is preferable that the compensation granule has been surface-treated in advance with a surface treatment agent (binder) having a high affinity for the monomer or the composition thereof or the generated polymer resin. Thereby, the dispersibility in the high molecular resin which comprises the matrix of the said particle | grains for compensation can be made high. The treatment with the surface treatment agent can be performed as a polymerization reaction and a series of steps.
[0052]
In the present invention, a polymer resin having transparency is produced by a polymerization reaction, and this is heated and melted, and then the compensation granules are added to the kneading and kneaded. A low birefringence optical resin material in which the body is uniformly dispersed can be produced.
[0053]
Alternatively, the target optical resin can also be obtained by a method in which the compensation particles are added and uniformly dispersed in a solution obtained by dissolving the polymer resin in an appropriate solvent, and then the solvent is removed by evaporation or the like. The material can be manufactured.
According to such a method of mixing the compensation particles into the polymer resin solution, it is easy to sufficiently uniformly disperse the fine powdery compensation particles, and the polymer resin is heated. Since it is not necessary, the thermal degradation does not occur, and the optical properties and mechanical properties of the polymer resin are not impaired. As a result, an optical resin material having good properties can be obtained. It is also possible to use the solution in which the compensation particles are dispersed in the production of a product such as a film as it is.
Also in these methods, it is preferable to use a compensation granule that has been surface-treated in advance with an appropriate surface treatment agent.
[0054]
The optical resin material mixed with the compensation particles obtained by the method as described above usually does not exhibit birefringence because the polymer chain of the polymer resin is not oriented as it is. .
The optical resin material in which the compensation particles are mixed is used as a raw material for various optical components and optical materials. However, as in the case of ordinary optical resin materials, production of practical products is possible. In order to use for this, it is preferable to pelletize by an appropriate means. The pelletized optical resin material is molded into a desired shape by a normal molding technique excellent in mass productivity such as injection molding or extrusion molding to obtain a product.
[0055]
In the matrix of the polymer resin forming such a molded product, the polymer chain is oriented in a specific direction due to the action of external force in the molding process, and thus orientation birefringence occurs. As a result, the compensation granules mixed in are present in a distribution that is sparse in the orientation direction of the polymer chain of the polymer resin body and dense in the direction intersecting the orientation direction. The birefringence of the optical resin material as a whole is compensated for by the distribution birefringence of the optical resin material. Is reduced.
[0056]
For example, in the injection molding process, polymer chains are oriented because high shear stress is generated in the polymer resin near the wall of the mold or near the gate of the mold, and in the extrusion molding process, Although orientation occurs in the polymer chain of the polymer resin during take-up or the like, the orientation birefringence due to the orientation of these polymer chains is reduced in a compensatory manner.
In addition, when a film made of a polymer resin mixed with compensation particles is stretched, the orientation of the polymer chain of the polymer resin occurs, so that when the compensation particles are not contained, orientation birefringence However, when the compensation granules are mixed, the stretched film obtained has low birefringence.
[0057]
That is, the molded optical resin material and the stretched optical resin material obtained as described above have extremely low birefringence, and the extent thereof is the content of the compensation particles and the degree of orientation. Depending on other conditions, there may be non-birefringence that does not exhibit birefringence in nature.
In addition, the presence of the compensation particles in the polymer resin may increase the fluidity of the polymer resin. In this case, the orientation of the polymer chain of the polymer resin in the molding process or the stretching process As a result, the effect of suppressing the orientation birefringence of the polymer resin is obtained, and this also makes the optical resin material low birefringent.
In this specification, the term “low birefringence” simply includes the case of non-birefringence.
[0058]
The optical resin material according to the present invention as described above can be used as a material for various optical components by taking advantage of the above characteristics, and these optical components can be used for various optical devices.
If it demonstrates concretely, the optical resin material by this invention will have high usefulness especially as a member for liquid crystal elements. A specific example thereof is a liquid crystal element substrate disposed so as to be interposed between a liquid crystal layer and a polarizing plate, for example. That is, the substrate formed of the optical resin material according to the present invention has no birefringence or low birefringence, and can be sufficiently used as a substrate for a liquid crystal element. When compared, the advantage of being an optical resin material is effectively utilized, and a liquid crystal device having good performance can be advantageously provided.
[0059]
The polarizing plate for a liquid crystal element is formed by bonding a transparent resin sheet on both sides of a polarizer. As the transparent resin sheet, a sheet made of the optical resin material according to the present invention can be used. As in the case of the substrate, a liquid crystal device having good performance can be advantageously provided.
[0060]
Furthermore, the optical resin material according to the present invention can be used as an adhesive for adhering each component forming the liquid crystal element. Such an adhesive is preferable in that it has a low birefringence per se and a great degree of freedom can be obtained in the selection of the constituent materials. That is, conventionally, an adhesive made of a resin having low birefringence has not been provided. Therefore, except for cases where a certain degree of birefringence is allowed, such as a monochrome type, bonding of each component is not possible. However, an adhesive made of the optical resin material according to the present invention can be used as an alternative to this adhesive, which improves the performance of the liquid crystal element in terms of durability and heat resistance. Can be improved.
[0061]
FIG. 3 is a cross-sectional view for explaining an example of the configuration of the liquid crystal element. In this example, 10 is a liquid crystal layer, 11a and 11b are substrates disposed above and below the liquid crystal layer, and 12a and 12b are polarizing plates disposed on the outer surfaces of the substrates 11a and 11b, respectively. Each of these comprises a transparent resin sheet 14 bonded to both surfaces of a polarizer 13.
In the liquid crystal element having such a configuration, the substrates 11a and 11b and the transparent resin sheet 14 can be formed of the optical resin material according to the present invention, and the substrates 11a and 11b and the polarizing plates l2a and 12b can be joined. Therefore, an adhesive using the optical resin material according to the present invention as a raw material can be used.
[0062]
FIG. 4 is an explanatory cross-sectional view showing another configuration example of the liquid crystal element. In this example, 10 is a liquid crystal layer, 15a and 15b are substrates disposed above and below the liquid crystal layer, and polarizing plates 16a and 16b are the substrates 15a and 15b and polarizers disposed on the outer surface thereof, respectively. 13 and a transparent resin sheet 14 bonded on the outer surface of the polarizer 13 are laminated. That is, each substrate 15a, 15b is the structure which served as the transparent resin sheet 14 by the side of the liquid crystal layer 10 in the structure of FIG. 3, and each polarizing plate 16a, 16b is integrated with each substrate 15a, 15b.
Also in the liquid crystal element having such a configuration, the substrates 15a and 15b and the transparent resin sheet 14 can be formed of the optical resin material according to the present invention, and the optical resin material according to the present invention is used as a raw material for bonding. An adhesive can be used.
[0063]
In addition, a ring-opening polymer obtained from the norbornene derivative represented by the general formula (1) described above or a hydrogenated polymer thereof as a polymer resin, in which compensation particles are mixed, has high transparency. This optical resin material has excellent heat resistance and low birefringence, and is particularly advantageous for the production of optical disks.
[0064]
【Example】
Examples of the present invention will be described below, but the present invention is not limited thereto.
<Example 1>
In this embodiment, as a polymer resin, a copolymer having a refractive index of 1.52 obtained by copolymerizing methyl methacrylate and benzyl methacrylate in a molar ratio of 78:22 is used. As the body, a grain having a maximum particle diameter of 100 nm made of adamantane having a refractive index of 1.49 was used. This adamantane is a low molecular weight substance that is isotropic with respect to polarization.
Then, the above-mentioned polymer resin is heated and melted, and an optical resin material is prepared by adding the compensation particles in an amount such that the ratio to the polymer resin is 5% by weight and kneading sufficiently. The film having a thickness of 100 μm was manufactured by extrusion molding. This is designated as “Sample 1”.
[0065]
The film of sample 1 was subjected to uniaxial stretching treatment under conditions of a stretching temperature of 80 ° C., a stretching speed of 4 mm / min, and a stretching ratio of 3.5 times, and the birefringence value Δn of the obtained stretched film was obtained. , -3.11 × 10^-6Met.
Further, the film of Sample 1 was subjected to uniaxial stretching treatment by variously changing the stretching treatment conditions, and the birefringence value Δn of the obtained stretched film was obtained. The results are as shown in Table 1.
[0066]
On the other hand, a reference film was produced in the same manner as Sample 1, except that the polymer resin was used as it was without adding any compensation granules. This is referred to as “reference sample 1”.
The film of the reference sample 1 was subjected to uniaxial stretching treatment under conditions of a stretching temperature of 90 ° C., a stretching speed of 4 mm / min, and a stretching ratio of 3.0 times, and a birefringence value Δn of the obtained stretched film was obtained. However, 1.23 × 10^-FiveMet.
Further, the film of sample 1 was subjected to uniaxial stretching treatment while changing the stretching treatment conditions, and the birefringence value Δn of the obtained stretched film was determined. The results are as shown in Table 1.
[0067]
[Table 1]

[0068]
From the results of Table 1, first, in the case of Sample 1 and Reference Sample 1, the birefringence value Δn of the obtained film is different if the stretching treatment conditions are different. It is understood that it is expressed.
And in the case of the reference sample 1 in which no compensation granule is contained in the polymer resin, the birefringence value Δn is positive under any stretching condition, whereas the compensation granule is contained. In this case, the birefringence value Δn of the entire film is negative. Therefore, by performing the stretching treatment under appropriate conditions, the birefringence changes and an optical resin material having low birefringence is obtained. It is understood that
This is because the degree of orientation of the polymer chain of the polymer resin differs depending on the degree of the stretching treatment, and as a result, the degree of orientation birefringence of the polymer resin and the degree of distribution birefringence due to the compensation particles change. This is probably because the birefringence of the entire film after compensation by the latter is different.
From the above, it is clear that an optical resin material having low birefringence can be obtained by mixing granules having an appropriate refractive index in appropriate proportions as granules for compensation into a polymer resin having transparency. It is.
[0069]
<Example 2>
8-methyl-8-carboxymethyltetracyclo [4.4.0.1 represented by the following structural formula (1)^2,5.1^7,10] 250 parts by weight of dodecene, 41 parts of 1-hexene and 750 parts by weight of toluene were charged into a reaction vessel substituted with nitrogen gas, and heated to 60 ° C. To this, 0.62 parts by weight of a toluene solution of triethylaluminum (1.5 mol / l) and a tungsten hexachloride solution modified with t-butanol / methanol (concentration 0.05 mol / l, t-butanol: methanol: Tungsten = 0.35: 0.3: 1) 3.7 parts by weight was added as a catalyst, and the mixture was heated and stirred at 80 ° C. for 3 hours to obtain a ring-opening polymer solution (a).
The polymerization conversion rate in this polymerization reaction was 97%. In addition, the intrinsic viscosity (η_inh) Was 0.45 dl / g (in chloroform, 30 ° C., concentration 0.5 g / dl).
[0070]
[Chemical 2]

[0071]
4000 parts by weight of the thus obtained ring-opening polymer solution (a) was put in an autoclave, a hydrogenation catalyst was added thereto, and a hydrogen gas pressure was 100 kg / cm.²Then, hydrogenation was performed by heating for 3 hours at a reaction temperature of 165 ° C.
The hydrogenated polymer thus obtained was poured into a large amount of methanol to solidify the polymer. The hydrogenation rate of the hydrogenated polymer obtained here was substantially 100 mol%.
[0072]
In a toluene solution of the above hydrogenated polymer, substantially spherical silica fine powder “Aerosil 300” (manufactured by Nippon Aerosil Co., Ltd.) having an average particle diameter of about 7 nm is added in an amount of 0.1% by weight based on the polymer. A silica dispersion solution was prepared at a ratio of
Using this silica dispersion solution, a film having a thickness of 100 μm after drying was prepared by a solution casting method. This is designated as Sample 2.
The film of Sample 2 was stretched under conditions of a stretching temperature of 170 ° C., a stretching speed of 8 mm / min, and a stretching ratio of 3.0 times. And when birefringence value (DELTA) n of the obtained stretched film was calculated | required, it was 1.32 * 10.^-3Met.
On the other hand, a film was prepared in the same manner as described above except that a solution containing no silica fine powder was used, and this was used as a reference sample 2 and subjected to the same stretching treatment, and the birefringence value Δn of the obtained stretched film was obtained. As a result, 1.92 × 10^-3Met.
From this, it is clear that the stretched film according to Sample 2 has reduced birefringence due to the presence of fine silica powder.
[0073]
【The invention's effect】
According to the present invention, even if the polymer resin constituting the matrix is birefringent by itself, particles for birefringence compensation having specific conditions are mixed and distributed. Due to the distributed birefringence caused by this, the birefringence of the polymer resin is compensated, and an optical resin material with reduced birefringence can be obtained.
In particular, when the polymer chain of the polymer resin is oriented, the distribution of the birefringence compensating granules is sparse in the polymer chain orientation direction of the polymer resin body and dense in the direction intersecting the orientation direction. With such a distribution, the orientation birefringence in the polymer resin is compensated by the distribution birefringence generated by the birefringence compensating particles, and thus low birefringence can be reliably obtained.
[0074]
In addition, the polymer resin is basically not restricted, and therefore, even if the sign of its own birefringence is positive or negative, an optical resin material having low birefringence is reliably provided. Can do. As a result, since the polymer resin can be freely selected from a wide range, a low birefringence optical resin material using a polymer resin having suitable characteristics depending on the intended use Therefore, it is possible to advantageously provide a low birefringence optical resin material having, for example, excellent optical properties, mechanical properties, or particularly high heat resistance.
[0075]
In addition, by using the low birefringence optical resin material of the present invention, various optical components having low birefringence can be formed, and equipment including optical elements affected by birefringence, for example, a configuration of a liquid crystal device The elements can be advantageously provided and various performances can be improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of the state of an oriented polymer chain of a polymer resin and the birefringence that is expressed.
FIG. 2 is an explanatory diagram of a refractive index ellipsoid.
FIG. 3 is an explanatory cross-sectional view illustrating an example of a configuration of a liquid crystal element.
FIG. 4 is an explanatory cross-sectional view illustrating another configuration example of the liquid crystal element.
[Explanation of symbols]
1 bond unit
2 Ellipse mark
3 Refractive index ellipsoid
10 Liquid crystal layer
11a, 11b substrate
12a, 12b Polarizing plate
13 Polarizer
14 Transparent resin sheet
15a, 15b substrate
16a, 16b Polarizing plate

Claims (11)

In the polymer resin having transparency, particles for birefringence compensation smaller than the wavelength of light are mixed,
The birefringence compensating granule is a granule made of a substance having an isotropic property with respect to polarization or a granule having an isotropic property with respect to the shape ,
The polymer resin has its polymer chain oriented by an external force, and the distribution of the birefringence compensating particles in the polymer resin body is sparse in the orientation direction of the polymer chain of the polymer resin body. Dense in the direction intersecting with
A low birefringence optical resin material characterized in that orientation birefringence in a polymer resin is compensated by distributed birefringence generated by a birefringence compensating particle . 2. The low birefringence optical resin material according to claim 1, wherein the polymer resin is a ring-opening polymer of a norbornene derivative . 3. The low birefringence optical resin material according to claim 1, wherein the birefringence compensating particles are particles made of adamantane or particles made of spherical silica . 4. A method for producing the low birefringence optical resin material according to claim 1, comprising a step of stretching a polymer resin having transparency mixed with particles for birefringence compensation. A method for producing a low birefringence optical resin material. An optical component comprising the low birefringence optical resin material according to any one of claims 1 to 3 . An optical apparatus using the optical component according to claim 5 as an optical element . An adhesive for optical parts, comprising the low birefringence optical resin material according to claim 1 and used for joining optical parts or optical elements . A substrate for a liquid crystal element, comprising the low birefringence optical resin material according to claim 1 and interposed between a liquid crystal layer and a polarizing plate in the liquid crystal element. A sheet made of the low birefringence optical resin material according to claim 1 is bonded to both surfaces of a polarizer for a liquid crystal element, and a polarizing plate for a liquid crystal element. An adhesive for liquid crystal elements, comprising the low birefringence optical resin material according to claim 1, and used for joining components forming a liquid crystal element. An optical disc comprising the low birefringence optical resin material according to claim 2 .

Images