JP2004346199A - Method for producing optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an optical film by which the optical film suitably usable as a phase difference film or the like, and having excellent optical isotropy is provided by a melt extrusion method by a T-die in high productivity. <P>SOLUTION: The method for producing the optical film comprises taking off the film at 10-100 m/min take-off speed when producing the film by extruding 70-40 wt.% maleimide-olefin copolymer having 1×10<SP>3</SP>-5×10<SP>6</SP>number average molecular weight, and 30-60 wt.% acrylonitrile-styrene copolymer containing 21-45 wt.% acrylonitrile unit by the melt extrusion method by the T-die, and forming the film on one or more cooling rollers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

（Ｒ^１は水素又は炭素数１〜６のアルキル基を示す。）
【００１６】
【化４】

（Ｒ^２、Ｒ^３はそれぞれ独立して水素又は炭素数１〜６のアルキル基を示す。）
【００１７】
【発明の実施の形態】
以下、本発明について詳細に説明する。
【００１８】
本発明の製造方法は、樹脂組成物として、上記一般式（Ｉ）で示される単位４０〜６０モル％、上記一般式（ＩＩ）で示される単位６０〜４０モル％からなる共重合体であり、数平均分子量が１×１０^３以上５×１０^６以下であるマレイミド・オレフィン共重合体７０〜４０重量％、アクリロニトリル単位２１〜４５重量％を含むアクリロニトリル・スチレン共重合体３０〜６０重量％からなる樹脂組成物を用いてなるものである。
【００１９】
ここで、Ｒ^１として水素又は炭素数１〜６のアルキル基であり、炭素数１〜６のアルキル基としては、例えばメチル基、エチル基、プロピル基、イソプロピル基、ブチル基、ｓ−ブチル基、ｔ−ブチル基、ペンチル基、ヘキシル基、シクロプロピル基、シクロブチル基、シクロヘキシル基等を挙げることができ、その中でも、特に耐熱性、成形性に優れる光学フィルムが得られることからメチル基であることが好ましい。又、Ｒ^２及びＲ^３は各々独立して水素又は炭素数１〜６のアルキル基であり、炭素数１〜６のアルキル基としては、例えばメチル基、エチル基、プロピル基、イソプロピル基、ブチル基、ｓ−ブチル基、ｔ−ブチル基、ペンチル基、ヘキシル基、シクロプロピル基、シクロブチル基、シクロヘキシル基等を挙げることができ、その中でも、特に耐熱性、成形性に優れる光学フィルムが得られることからメチル基であることが好ましい。
【００２０】
そして、このようなマレイミド・オレフィン共重合体は、例えばマレイミド類とオレフィン類とのラジカル共重合反応により得ることができる。その際、一般式（Ｉ）で示される単位を誘導する化合物としては、例えばマレイミド、Ｎ−メチルマレイミド、Ｎ−エチルマレイミド、Ｎ−ｎ−プロピルマレイミド、Ｎ−ｉ−プロピルマレイミド、Ｎ−ｎ−ブチルマレイミド、Ｎ−ｉ−ブチルマレイミド、Ｎ−ｔ−ブチルマレイミド、Ｎ−ｎ−ペンチルマレイミド、Ｎ−ｎ−ヘキシルマレイミド、Ｎ−シクロプロピルマレイミド、Ｎ−シクロブチルマレイミド、Ｎ−シクロヘキシルマレイミド等のマレイミド類が例示され、耐熱性、機械特性、透明性に優れる光学フィルムが得られることから特にＮ−メチルマレイミドが好ましい。さらに、これら化合物は１種または２種以上組み合わせて用いることができる。
【００２１】
また、一般式（ＩＩ）で示される単位を誘導する化合物としては、例えばイソブテン、２−メチル−１−ブテン、２−メチル−１−ペンテン、２−メチル−１−ヘキセン等のオレフィン類が例示でき、このうち耐熱性、機械特性、透明性に優れる光学フィルムが得られることから特にイソブテンが好ましい。また、これら化合物は１種または２種以上組み合わせて用いることができる。
【００２２】
マレイミド・オレフィン共重合体における一般式（Ｉ）で示される単位は、４０〜６０モル％であり、特に耐熱性、機械特性に優れる光学フィルムとなることから４５〜５５モル％であることが好ましい。ここで、一般式（Ｉ）で示される単位が６０モル％を越える場合、得られる光学フィルムは脆くなる。一方、４０モル％未満の場合、得られる光学フィルムの耐熱性が低下する。
【００２３】
更に、マレイミド・オレフィン共重合体は、必要に応じ本発明の目的を損なわない範囲で他のモノマー成分より誘導される単位を含有するものであってもよく、そのような他のモノマー成分としては、例えばスチレン、α−メチルスチレン等のスチレン誘導体；メタクリル酸、メタクリル酸メチル、メタクリル酸エチル等のメタクリル酸又はそのエステル類；アクリル酸、アクリル酸メチル、アクリル酸エチル等のアクリル酸又はそのエステル類；酢酸ビニル、安息香酸ビニル等のビニルエステル類；メチルビニルエーテル、エチルビニルエーテル、プロピオビニルエーテル、ブチルビニルエーテル等のビニルエーテル類；無水マレイン酸；アクリロニトリルより選ばれる１種類以上の化合物が挙げられ、その含有率としては５モル％以下であることが好ましい。
【００２４】
マレイミド・オレフィン共重合体は、公知の重合方法、例えば塊状重合法、溶液重合法、懸濁重合法、沈殿重合法、及び乳化重合法のいずれもが採用可能であり、その中でも透明性、色調に優れる光学フィルムが得られることから沈殿重合法により得られるものであることが好ましい。
【００２５】
重合反応の際に用いる重合開始剤としては、例えばベンゾイルパーオキサイド、ラウリルパーオキサイド、オクタノイルパーオキサイド、アセチルパーオキサイド、ジ−ｔ−ブチルパーオキサイド、ｔ−ブチルクミルパーオキサイド、ジクミルパーオキサイド、ｔ−ブチルパーオキシアセテート、ｔ−ブチルパーオキシベンゾエート等の有機過酸化物；２，２’−アゾビス（２，４−ジメチルバレロニトリル）、２，２’−アゾビス（２−ブチロニトリル）、２，２’−アゾビスイソブチロニトリル、ジメチル−２，２’−アゾビスイソブチレート、１，１’−アゾビス（シクロヘキサン−１−カルボニトリル）等のアゾ系開始剤、等が挙げられる。
【００２６】
溶液重合法、沈殿重合法において用いられる溶媒としては、例えばベンゼン、トルエン、キシレンなどの芳香族溶媒；メタノール、エタノール、プロピルアルコール、ブチルアルコールなどのアルコール系溶媒；シクロヘキサン、ジオキサン、テトラヒドロフラン、アセトン、メチルエチルケトン、ジメチルホルムアミド、酢酸イソプロピル、芳香族系溶媒とアルコール系溶媒の混合溶媒などが挙げられる。
【００２７】
その際の重合温度は、開始剤の分解温度に応じて適宜設定することができるが、一般的には４０〜１５０℃の範囲で行うことが好ましい。
【００２８】
また、マレイミド・オレフィン共重合体は、別法として無水マレイン酸・オレフィン共重合体をアンモニア及び／又はアルキルアミンを用いて、後イミド化することによっても得ることができる。
【００２９】
このような後イミド化反応は、例えば無水マレイン酸・オレフィン共重合体をメタノール、エタノール、プロパノールなどのアルコール溶媒；ベンゼン、トルエンなどの芳香族系溶媒；酢酸エチル、酢酸イソプロピルなどのエステル系溶媒；芳香族系溶媒とアルコール系溶媒の混合溶媒などに溶解あるいは分散させ、アンモニア及び／又はアルキルアミンと５０〜２５０℃の温度で反応させることによりアミド化反応とイミド化反応を連続的に行う方法、アンモニア及び／又はアルキルアミンと反応させてアミド体を得た後、該アミド体を加熱して脱水閉環させ、イミド化を行う方法、等により製造することができる。
【００３０】
本発明に用いられるマレイミド・オレフィン共重合体は、数平均分子量（Ｍｎ）が１×１０^３以上５×１０^６以下であり、特に機械特性とフィルム加工性のバランスに優れることから１×１０^４以上５×１０^５以下が好ましい。数平均分子量が５×１０^６を超える場合、マレイミド・オレフィン共重合体の溶融粘度が高くなりすぎるため、Ｔダイ溶融押出における樹脂の流動性が乏しくなり、厚み精度や表面平滑性に劣る光学フィルムとなる。一方、数平均分子量が１×１０^３未満の場合、得られる光学フィルムの機械強度が乏しくなる。ここで、本発明における数平均分子量とは、ゲル・パーミエーション・クロマトグラフィ（ＧＰＣ）により求めた標準ポリスチレン換算値のことである。
【００３１】
本発明で使用されるアクリロニトリル・スチレン共重合体としては、アクリロニトリル単位を２１〜４５重量％含むアクリロニトリル・スチレン共重合体である。ここで、アクリロニトリル単位が２１重量％未満、又は、４５重量％を越える場合、上記マレイミド・オレフィン共重合体とアクリロニトリル・スチレン共重合体との相溶性が低下し、得られるフィルムは不透明になり、また耐熱性も低下する。
【００３２】
本発明におけるマレイミド・オレフィン共重合体とアクリロニトリル・スチレン共重合体の配合割合は、マレイミド・オレフィン共重合体７０〜４０重量％とアクリロニトリル・スチレン共重合体３０〜６０重量％であり、特に加工性、耐熱性、光学特性のバランスに優れた光学フィルムが得られることからマレイミド・オレフィン共重合体７０〜５０重量％とアクリロニトリル・スチレン共重合体３０〜５０重量であることが好ましい。マレイミド・オレフィン共重合体が４０重量％未満である場合、フィルムの耐熱性および光学等方性が乏しくなるため好ましくなく、また、マレイミド・オレフィン共重合体が７０重量％を超える場合には、フィルムの光学等方性が乏しくなるため好ましくない。
【００３３】
本発明でいうフィルムの光学等方性とは、３次元的な屈折率の均質性を指し、光学等方性が最も高い理想的なフィルムの場合、フィルムの全ての方向で屈折率が均一となる。また、この光学等方性の定量化には、一般的にフィルム面内および厚み方向の位相差が用いられる。位相差は複屈折と光路長の積として定義され、また複屈折はある特定の方向の屈折率とその方向に直交する方向の屈折率の差として定義される。従って、どの方向にそって位相差を測定しても小さい値となるフィルムが光学等方性に優れることになる。
【００３４】
そして、本発明の製造方法は、光学等方性に優れる光学フィルムの製造方法に関するものであり、得られる光学フィルムは、フィルム面方向の位相差が１０ｎｍ以下であり、厚み方向の位相差が５０ｎｍ以下である光学フィルムであることが好ましく、これら位相差は小さいければ小さいほど本発明により得られる光学フィルムとして好ましい。
【００３５】
本発明の製造方法は、上記した樹脂組成物をＴダイ溶融押出法により溶融フィルムとして押し出し、一個又は複数個の冷却ロールにて冷却しフィルムを製造する際に、引き取り速度１０ｍ／分〜１００ｍ／分の範囲で引き取ることを特徴とする光学フィルムの製造方法に関するものであり、本発明の光学フィルムの製造に用いることのできるフィルム製造装置の一例を図１に示し、本発明の説明を行うが本発明はこの製造装置によりなんら限定されるものではなく、さらに付加的装置等を付加した装置等であってもよい。
【００３６】
ここで、図１中の符号は以下のもの、１：二軸押出機、２：真空ベント、３：ダイバーターバルブ、４：ギアポンプ、５：スクリーンチェンジャー、６：Ｔダイ、７：第１冷却ロール、８：巻取りフィルム、のそれぞれを示す。
【００３７】
本発明でいうＴダイ溶融押出法とは、押出機内で溶融混練した樹脂をＴダイからフィルム状に押出し、この溶融フィルムを冷却ロールで冷却しつつ引き取ることを特徴とするフィルムの製造方法である。ここで、Ｔダイ溶融押出法では、溶融したフィルムを引き取る際にフィルムに張力が加わり、得られるフィルムは分子配向による複屈折が生じ易いことが一般的であり、従来、該Ｔダイ溶融押出法により光学等方性に優れる光学フィルムを製造する際には、できる限りフィルムに張力を与えず、分子配向による複屈折が生じないように、例えば、１０ｍ／分未満という低速度で引き取ることが必要であった。つまり、Ｔダイ溶融押出法は、表面平滑性の高いフィルムを高い生産性で製造できる方法として広く一般的に知られるにもかかわらず、光学等方性に優れた光学フィルムを製造するためには、その特徴が活かし切れていないことが実状である。
【００３８】
これに対し、本発明の光学フィルムの製造方法は、Ｔダイ溶融押出法により１０ｍ／分〜１００ｍ／分という高速で光学フィルムを引き取ることを特徴とし、光学等方性に優れる光学フィルムを高い生産性で製造することができる。フィルムの引き取り速度は上記範囲であれば、特に制限はなく、引き取り速度の上昇により厚み精度が低下する傾向にあるため、生産性と厚み精度や光学特性のバランスを考慮して、適宜選択すればよい。
【００３９】
また、Ｔダイ溶融押出法において、上記引き取り速度の他、フィルム特性に影響を与える成形条件として、溶融樹脂の温度、冷却ロールの表面温度、その中でも特に冷却ロールが複数個ある場合のＴダイ側の最も上流位にある第１冷却ロールの表面温度が挙げられる。そして、本発明の製造方法において、溶融樹脂の温度は、吐出量や厚み等に応じて適宜選択すればよく、その中でも溶融樹脂の熱分解によるフィルム外観性の悪化を避けるため、樹脂を溶融させた後Ｔダイから吐出されるまでの間を３００℃以下に維持することが好ましく、２９０℃以下であることが特に好ましい。
【００４０】
冷却ロールの温度、特に第１冷却ロールの温度設定は、得られる光学フィルムの外観性や光学特性に与える影響の大きい重要な製造条件の一つであり、溶融フィルムの冷却ロールへの密着性および離型性のバランスを考慮して最適化されるものであり、本発明の製造方法においては、溶融フィルムの冷却ロールへの密着性が十分保持され、フィルム表面の筋模様の発生が抑制され、均一な厚みを有する光学フィルムが得られることから、冷却ロールの表面温度、特に第一冷却ロールの表面温度を示差走査熱量計（以下、ＤＳＣという。）により昇温速度１０℃／ｍｉｎで測定した樹脂組成物のガラス転移温度−４０℃〜ガラス転移温度＋２０℃とすることが好ましく、特に樹脂組成物のガラス転移温度−３５℃〜樹脂組成物のガラス転移温度＋１０℃とすることが好ましい。
【００４１】
本発明におけるＴダイ溶融押出法の上記以外の成形条件として、スクリュー回転数、吐出量等が挙げられるが、これら条件はフィルムの厚みや引き取り速度等に応じて適宜選択すればよい。また、溶融樹脂の酸化による熱分解や黄変を抑制するため、ホッパー、押出機シリンダー内部等を窒素パージあるいは真空にすることが好ましい。
【００４２】
以下に、本発明の製造方法を実施する際の成形装置、付加的成形装置の一例について述べるが、本発明はこれらに制限されるものではない。
【００４３】
本発明に用いることのできる押出機としては、例えば単軸押出機、同方向回転二軸押出機、異方向回転二軸押出機、タンデム型押出機等が代表例として挙げられる。成形に供される樹脂組成物に水などの揮発性成分が含まれていると、光学フィルム押出時にフィルム外観性が悪化するため、これら押出機は揮発性成分を除去するための真空ベント、ホッパドライヤー等が具備されたものが適宜使用される。また、シリンダ径、Ｌ／Ｄ、圧縮比、スクリューデザインは一般的に生産速度、フィルムの寸法などに応じて最適化すればよく、特に光学フィルムの製造の際には、吐出速度を安定化させるとともに、摩擦発熱の抑制や樹脂温度を分解温度以下に維持することを目的に最適化すればよい。
【００４４】
本発明の製造方法においては、吐出速度を安定化させ、光学フィルムの流れ方向の厚み精度を向上させる為に、昇圧機能および計量機能を備えたギアポンプを押出機と組み合わせて用いることが好ましい。また、後述するフィルターシステムに溶融樹脂を通過させて異物をろ過する場合、容器内の圧力損失が押出機の押出圧力を上回る場合などでは、ギアポンプで昇圧することが必要となる。ただし、溶融樹脂がギアポンプ内で滞留し、熱分解あるいは黄変する可能性があるため、滞留を防止できるような構造であることが望ましい。
【００４５】
また、溶融樹脂に含まれる繊維、金属、砂、樹脂あるいは添加物等の凝集物などに代表される異物を除去する目的、および押出機やギアポンプ内で発生した樹脂劣化物を除去する目的で、Ｔダイ溶融押出工程内にフィルターを設置することが好ましく、そのようなフィルターは一般的にはスクリーンメッシュと呼ばれるステンレス等の合金からなる金網の単層体を用いて異物をろ過するものでもよいが、特に光学フィルムを製造する場合には、フィルムの外観に対する要求が非常に厳しいため、上記スクリーンメッシュによるろ過では異物が除去しきれない場合がある。このような場合には、上記ステンレス等の合金からなる金網を積層し、各層を焼結したフィルター、ステンレス鋼の微細繊維を複雑に編み込んだ金網にて繊維間の接点を焼結したフィルター、金属粉末を焼結したフィルター（以下、これらを総称して焼結金属フィルタ−と述べる。）などを用いることが好ましく、該焼結金属フィルターはスクリーンメッシュに対して、高いろ過効率および低いろ過抵抗が得られることが一般的に知られている。該焼結金属フィルターは、例えば特開平０７−１２４４２６号公報、特開平０８−１０５２１号公報、特開平１０−３３７４１５号公報、特開平１１−７６７２１号公報などに開示されている。また、焼結金属フィルターをチューブ状やディスク状の形状として容器に多数組み込んだフィルターシステムに溶融樹脂を通過させて異物をろ過する方法が例えば特開平０８−１０５２２号公報などに開示されており、焼結金属フィルターを単独で用いるよりも、さらに高いろ過効率および低いろ過抵抗が得られるため、本発明の製造方法にて好適に使用することができる。ただし、溶融樹脂がフィルターシステム内で熱分解あるいは黄変する可能性があるため、フィルターシステム内の滞留時間には注意する必要があり、また、フィルターシステムは、デットスペース等に滞留が起こり難いような構造であることが望ましい。
【００４６】
本発明の製造方法において、溶融樹脂はＴダイ内で幅広のフィルムに賦形されるため、フィルムの寸法は主にＴダイよって決定される。Ｔダイ内の流路は、溶融樹脂の粘弾性特性に合わせて最適化すればよく、ダイスとしては一般的にストレートマニホールド型、コートハンガー型、フィッシュテール型、コートハンガーマニホールド型が挙げられ、その中でも得られる光学フィルムの厚み精度を重視する場合、マニホールド型のダイスを用いることが好ましい。また、溶融樹脂の出口部分であるリップの隙間調整は、フィルムの厚み精度を決定する重要な因子の一つである。
【００４７】
本発明の製造方法により得られる光学フィルムは、厚み精度の要求が非常に厳しく、その理由の一つとして、前述した位相差は光が透過する媒体の複屈折と光路長の積で定義されるため、仮に複屈折が均質であっても、フィルム厚みが不均質であると、位相差は不均質となり、フィルムの光学等方性が乏しくなるのである。しかし、リップの精密な厚み調整作業には熟練者を要しても時間が掛かるため、近年ではコンピューターを駆使した自動厚み制御システムが導入され、フィルム厚み精度の向上のみならず、歩留まりの向上に大きく寄与している。そして、そのような方法として、オンラインでフィルムの厚みを計測し、その結果をもとに自動でリップの隙間調整やギアポンプの速度調製を行う方法が挙げられ、例えば特開平１０−５８５１８号公報、特開２０００−１２７２２６号公報などに開示され、自動でリップを調整する方法としては、例えばヒートボルト方式、ロボット方式、リップヒータ方式、圧電素子方式などが挙げられ、本発明の製造方法においてもこれら方法を付加的に用いることもできる。
【００４８】
また、Ｔダイのリップは、溶融樹脂の出口部分であるため、溶融樹脂と接触するリップ部に凹凸がある場合、光学フィルム表面に凹凸が転写されてしまい、冷却ロールにより形状が固化され、いわゆるダイラインなどになる。よって、特に溶融樹脂と接触するリップ部は、電解研磨などの方法によって表面粗さを小さくすることが望ましい。さらにリップ部の表面粗さが小さくても、熱分解した樹脂がリップ部に付着していわゆる目やにとなると、リップの表面に凹凸が生じることになりダイラインが発生する原因となる。目やに防止のためには、溶融樹脂がリップに付着し難くすることが重要であり、本発明の製造方法においてはクロムやセラミックでコートしたリップを好適に用いることができる。また、溶融樹脂と接触するリップのエッジ部分には樹脂が滞留し易いため、リップのエッジはできる限り鋭くすることが好ましく、特に０．１ｍｍＲ以下であることが好ましい。
【００４９】
本発明の製造方法においては、Ｔダイのスリットより押出された溶融樹脂（溶融フィルム）を冷却ロールに密着させて冷却する。このような冷却ロール、複数個ある場合の第一冷却ロールは一般的にキャストロールやキャスティングロールと呼ばれる。そして、溶融フィルムが接触する第一冷却ロールの表面は、Ｔダイのリップと同様の理由により、表面粗さが小さいことが望まれる。さらに、冷却ロールが複数個ある場合、第一冷却ロールとその他の冷却ロールは、ロールの回転速度を一定に保つことが重要であり、回転速度にムラがあると、フィルム表面に幅方向のスジが発生する場合がある。
【００５０】
そして、得られる光学フィルムをより効率的に冷却するためには、第一冷却ロールに巻き付かせた光学フィルムを第一冷却ロールの反対面から冷却する方法を用いることが好ましく、そのような方法としては、例えばエアーチャンバー法、タッチロール法、エアーナイフ法、ラバーロール法、冷却ドラム法、耳押えロール法、静電ピーニング法が挙げられる。また、タッチロール法として、例えば特開２００２−３６３３２号公報、特開ＷＯ９７／２８９５０号公報、特開平１１−２３５７４７号公報に弾性変形が可能なタッチロールが提案されており、これらの場合、高剛性のタッチロールを用いるよりも薄いフィルムが成形可能であり、本発明にもこれら方法を採用することができる。また、タッチロールでフィルムを第一冷却ロールの反対面から抑えることにより、表面粗さを平坦化させたり、引取り方向の分子配向を起こり難くさせる効果があるため、これらタッチロールは好ましく用いることができる。無論、第一冷却ロールの反対面からの冷却は特に行わず、放冷としてもよい。
【００５１】
冷却ロールの表面温度は、得られる光学フィルムの外観に大きく影響するため、冷却ロールの表面温度は０．１℃の精度で制御することが望ましく、その際は上述したようにＤＳＣで測定した樹脂組成物のガラス転移温度−４０℃〜＋２０℃に設定することが好ましく、その際、加圧水やオイルがロール温調の媒体として使用される。なお、温度制御の精度に優れることからオイル温調が好ましい。
【００５２】
得られる光学フィルムの両端部を切断するためのスリッターを設置してもよく、その際のスリッターに制限はない。その中でも、本発明により得られる光学フィルムは比較的に硬質であるため、フィルムの破断面に微細なクラックが発生することを抑制し易いため、回転刃をフィルムの両面から押さえつけて切断するシェアカッターと呼ばれるスリッターを用いることが好ましい。
【００５３】
また、得られた光学フィルム表面に繊維等の異物が付着することを防止するため、フィルムの片面、もしくは両面をマスキング処理することが好ましく、マスキング処理する装置を付加する事が好ましい。
【００５４】
得られた光学フィルムを巻取る為の巻取り機に特に制限はなく、その中でも引き取り速度と巻き取り速度のバランス調整を行うためのアキュムレーター設備を用いることが好ましい。
【００５５】
本発明の製造方法により得られる光学フィルムは、機械強度の向上、光学特性の調整など目的として延伸された光学フィルムであってもよく、延伸された光学フィルムを製造する際には、延伸加工工程を付加してもよい。そして、延伸加工工程はＴダイ溶融押出工程内で連続して行う工程、光学フィルムを一旦巻き取った後、該フィルムを延伸加工装置に供して延伸加工する工程、等がある。また、延伸方向はその目的により、一軸方向または二軸方向が選ばれ、一軸方向に延伸する場合、フィルム幅方向の長さが延伸前の長さに対して、延伸途中に変化しないよう拘束することが光学特性の均一な延伸フィルムを得るうえでより好ましい。一軸延伸方法として、テンターにより延伸する方法、カレンダーにより圧延して延伸する方法、ロール間で延伸する方法などが挙げられ、ニ軸延伸方法としてテンターにより延伸する方法、チューブ状に膨らませて延伸する方法などがある。
【００５６】
本発明により得られる光学フィルムを延伸された光学フィルムとする場合、その延伸条件としては、フィルムに厚みむらが発生し難く、得られるフィルムが機械的特性、光学的特性に優れることからＤＳＣで測定した樹脂組成物のガラス転移温度に対して１℃〜４０℃高い延伸温度条件のもと、延伸倍率１．１〜３倍の範囲に延伸することが特に好ましい。
【００５７】
本発明により得られる光学フィルムは、発明の主旨を超えない範囲で添加剤を含有してもよく、添加方法としては、樹脂組成物を製造する工程で添加する方法、Ｔダイ溶融押出工程にて樹脂組成物および添加剤をドライブレンドしてホッパーに供給し、押出機内で溶融混練する方法などが挙げられる。
【００５８】
そして、添加剤としては、例えば界面活性剤、高分子電解質、導電性錯体、無機フィラー、顔料、染料、酸化防止剤、ヒンダードアミン系光安定剤、紫外線吸収剤、帯電防止剤、アンチブロッキング剤、滑剤等の一般的な添加剤が挙げられ、以下にその詳細を示すが、本発明はこれらになんら制限されるものではない。
【００５９】
酸化防止剤としては、例えばヒンダードフェノール系酸化防止剤、リン系酸化防止剤、その他酸化防止剤が挙げられ、これら酸化防止剤はそれぞれ単独で用いてもよく、それぞれを併用して用いても良い。そして、相乗的に酸化防止作用が向上することからヒンダードフェノール系酸化防止剤とリン系酸化防止剤を併用して用いることが好ましく、その際には例えばヒンダードフェノール系酸化防止剤１００重量部に対してリン系酸化防止剤を１００〜５００重量部で混合して使用することが特に好ましい。また、酸化防止剤の添加量としては、樹脂組成物１００重量部に対して通常０．００１〜２重量部が好ましく、特に０．０１〜１重量部の範囲であることが好ましい。
【００６０】
ヒンダードフェノール系酸化防止剤としては、例えばペンタエリスリトール−テトラキス（３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート）、チオジエチレン−ビス（３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート）、オクタデシル−３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート、Ｎ，Ｎ’−ヘキサン−１，６−ジイルビス（３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオナミド）、ジエチル（（３，５−ビス（１，１−ジメチルエチル）−４−ヒドロキシフェニル）メチル）ホスフェート、３，３’，３’’，５，５’，５’’−ヘキサ−ｔ−ブチル−ａ，ａ’，ａ’’−（メシチレン−２，４，６−トリイル）トリ−ｐ−クレゾール、エチレンビス（オキシエチレン）ビス（３−（５−ｔ−ブチル−４−ヒドロキシ−ｍ−トリル）プロピオネート）、ヘキサメチレン−ビス（３−（３，５−ジ−ｔ−ブチル−４−ヒドロキシフェニル）プロピオネート）、１，３，５−トリス（３，５−ジ−ｔ−ブチル−４−ヒドロキシベンジル）−１，３，５−トリアジン−２，４，６（１Ｈ，３Ｈ，５Ｈ）−トリオン、１，３，５−トリス（（４−ｔ−ブチル−３−ヒドロキシ−２，６−キシリル）メチル）−１，３，５−トリアジン−２，４，６（１Ｈ，３Ｈ，５Ｈ）−トリオン、２，６−ジ−ｔ−ブチル−４−（４，６−ビス（オクチルチオ）−１，３，５−トリアジン−２−イルアミノ）フェノール、３，９−ビス（２−（３−（３−ｔ−ブチル−４−ヒドロキシ−５−メチルフェニル）プロピオニルオキシ）−１，１−ジメチルエチル）−２，４，８，１０−テトラオキサスピロ（５，５）ウンデカンなどが挙げられる。
【００６１】
リン系酸化防止剤としては、例えばトリス（２，４−ジ−ｔ−ブチルフェニル）フォスファイト、ビス（２，４−ビス（１，１−ジメチルエチル）−６−メチルフェニル）エチルエステル亜りん酸、テトラキス（２，４−ジ−ｔ−ブチルフェニル）（１，１−ビフェニル）−４，４’−ジイルビスホスフォナイト、ビス（２，４−ジ−ｔ−ブチルフェニル）ペンタエリスリトールジホスファイト、ビス（２，６−ジ−ｔ−ブチル−４−メチルフェニル）ペンタエリスリトールジホスファイト、ビス（２，４−ジクミルフェニル）ペンタエリスリトール−ジホスファイト、テトラキス（２，４−ｔ−ブチルフェニル）（１，１−ビフェニル）−４，４’−ジイルビスホスフォナイト、ジ−ｔ−ブチル−ｍ−クレジル−ホスフォナイト、などが挙げられる。
【００６２】
また、ヒンダードアミン系光安定剤を用いることができ、ヒンダードアミン系光安定剤としては、熱着色抑制効果に優れることから分子量が１，０００以上のものが好ましく、特に１，５００以上であることが好ましい。さらに、ヒンダードアミン系光安定剤の添加量は、熱着色防止効果および光安定化効果に優れることから樹脂組成物１００重量部に対して０．０１重量部〜１．５重量部を用いることが好ましく、特に０．０５重量部〜１．０重量部が好ましく、さらに０．１重量部〜０．５重量部であることが好ましい。
【００６３】
このようなヒンダードアミン系光安定剤としては、例えばポリ（（６−モルフォリノ−ｓ−トリアジン−２，４−ジイル）（（２，２，６，６−テトラメチル−４−ピペリジル）イミノ）ヘキサメチレン（（２，２，６，６−テトラメチル−４−ピペリジル）イミノ））（分子量１，６００）、ポリ（（６−（１，１，３，３−テトラメチルブチル）アミノ−１，３，５―トリアジン−２、４−ジイル）（（２，２，６，６−テトラメチル−４−ピペリジル）イミノ）ヘキサメチレン（（２，２，６，６−テトラメチル−４−ピペリジル）イミノ））（分子量２，０００〜３，１００）、ジブチルアミン−１，３，５−トリアジン−Ｎ，Ｎ’−ビス（２，２，６，６−テトラメチル−４−ピペリジル−１，６−ヘキサメチレンジアミン−Ｎ−（２，２，６，６−テトラメチル−４−ピペリジル）ブチルアミンの重縮合物（分子量２，６００〜３，４００）、Ｎ，Ｎ’−ビス（３−アミノプロピル）エチレンジアミン−２，４−ビス（ Ｎ−ブチル−Ｎ−（１，２，２，６，６−ペンタメチル−４−ピペリジル）アミノ）−６−クロロ−１，３，５−トリアジン縮合物（分子量２，０００以上）、コハク酸ジメチル−１−（２−ヒドロキシエチル）−４−ヒドロキシ−２，２，６，６−テトラメチルピペリジン縮合物（分子量３，１００〜４，０００）などが挙げられ、これらは一種類以上で用いることができる。
【００６４】
紫外線吸収剤として、例えばベンゾトリアゾール、ベンゾフェノン、トリアジン、ベンゾエートなどの紫外線吸収剤を必要に応じて添加することもできる。
【００６５】
また、本発明の製造方法においては、Ｔダイ溶融押出時の摩擦発熱の抑制、押出安定性の向上などを目的として滑剤を添加してもよく、滑剤の添加量は１〜１００００ｐｐｍが好ましく、特に５〜２０００ｐｐｍが好ましく、さらに１０〜５００ｐｐｍであることが好ましい。そのような滑剤としては、例えば流動パラフィン、天然パラフィン、ポリエチレンワックスなどの脂肪族炭化水素系滑剤；セチルアルコール、ステアリルアルコール、ステアリン酸などの高級脂肪族系アルコール・高級脂肪酸系滑剤；ステアリン酸アミド、オレイン酸アミド、パルミチン酸アミド、メチレンビスステアロアミドなどの脂肪族アマイド系滑剤；ステアリン酸カルシウム、ステアリン酸亜鉛、ステアリン酸マグネシウム、ステアリン酸バリウムなどの金属石鹸系滑剤；ステアリン酸ブチル、ステアリン酸エチレングリコールなどの脂肪酸エステル系滑剤；複合滑剤などが挙げられる。
【００６６】
本発明により得られる光学フィルムは、光学部品として用いられるフィルムとして優れたものとなることから光線透過率８５％以上、ヘイズ２％以下であるフィルムであることが好ましい。光学フィルムの厚みは、フィルムの厚み精度、機械特性、外観に優れるものとなることから１０〜３００μｍであることが好ましく、特に１０〜２００μｍであることが好ましい。
【００６７】
【実施例】
以下に本発明を実施例により詳細に説明するが、本発明はこれら実施例によりなんら制限されるものではない。
【００６８】
実施例に示された諸物性は以下の方法により測定した。
【００６９】
〜数平均分子量〜
ゲル・パーミエーション・クロマトグラフィー（ＧＰＣ）（東ソー株式会社製、商品名ＨＬＣ−８０２Ａ）を用い測定したマレイミド・オレフィン共重合体の溶出曲線により、標準ポリスチレン換算値として求めた。
【００７０】
〜マレイミド・オレフィン共重合体、アクリロニトリル・スチレン共重合体の組成比〜
元素分析、^１Ｈ−ＮＭＲ測定により求めた。
【００７１】
〜マレイミド・オレフィン共重合体のガラス転移温度〜
示差走査熱量計（セイコー電子工業株式会社製、商品名ＤＳＣ２００）を用い、昇温速度１０℃／分で測定した。
【００７２】
〜光学フィルムの全光線透過率〜
ＪＩＳ−Ｋ−７１０５を準拠し測定した。
【００７３】
〜光学フィルムの位相差〜
全自動複屈折計（王子計測機器株式会社製、商品名ＫＯＢＲＡ−２１ＡＤＨ）を用い、測定波長５９０ｎｍの条件で測定した３次元屈折率をもとに、下式よりフィルム面方向の位相差および厚み方向の位相差を求めた。
【００７４】
フィルム面方向の位相差（Ｒ）＝（Ｎｘ−Ｎｙ）ｄ
（ここで、Ｎｘ：フィルム面内における遅相軸方向の屈折率、Ｎｙ：フィルム面内における遅相軸方向に直交する方位の屈折率、ｄ：フィルム厚み、を示す。）
フィルム厚み方向の位相差（Ｋ）＝（（Ｎｘ＋Ｎｙ）／２−Ｎｚ）ｄ
（ここで、Ｎｘ：フィルム面内における遅相軸方向の屈折率、Ｎｙ：フィルム面内における遅相軸方向に直交する方位の屈折率、Ｎｚ：フィルム表面の法線方向の屈折率、ｄ：フィルム厚み、を示す。）
〜光学フィルムの厚み〜
ダイヤルゲージ（株式会社ミツトヨ製、商品名ＩＤ−Ｃ１２５Ｂ）を用いて光学フィルムの中心部を測定した。
【００７５】
〜光学フィルム厚みむら〜
光学フィルムの中心部および端部から１５ｍｍ中心側に位置する部分の厚みを測定し、２点間の厚みの差を厚みのむらとした。
【００７６】
合成例１（マレイミド・オレフィン共重合体の合成）
攪拌機、窒素導入管、温度計および脱気管の付いた反応釜にＮ−メチルマレイミド１００重量部に対し、ｔ−ブチルパーオキシネオデカノエート０．６７重量部およびトルエンとメタノールの混合溶媒（１：１重量比）１０５０重量部を仕込み、窒素で数回パージした後、イソブテン４００重量部を仕込み、６０℃で６時間反応を行った。得られた粒子を遠心分離後乾燥した。得られたポリマーの元素分析結果（Ｃ；６４．７重量％、Ｈ；７．８重量％、Ｎ；８．４重量％）より、生成ポリマー中のＮ−メチルマレイミド単位及びイソブテン単位は、それぞれ５０モル％であった。得られたポリマーの数平均分子量（Ｍｎ）は９０，０００であった。
【００７７】
参考例１〜２、参考比較例１〜３
合成例１によりＮ−メチルマレイミド・イソブテン共重合体と表１に記載のアクリロニトリル含量の異なるアクリロニトリル・スチレン共重合体を５０：５０の重量比にてドライブレンドし、３０ｍｍφ２軸押出機（株式会社日本製鋼所製、商品名ＴＥＸ３０）に供し、溶融混練の後、２３０℃〜２５０℃で押し出してペレタイズした。得られた樹脂組成物ペレットを２２０℃で５分間の条件で熱プレス成形し、厚み１００μｍのフィルムとした。本フィルムの物性測定結果について表１に示す。
【００７８】
これらの結果より明かなように、参考例１，２により得られたフィルムは単一のガラス転移温度を示し、優れた光線透過率を示す。一方、アクリロニトリル含量が少量又は多量のアクリロニトリル・スチレン共重合体を用いた参考比較例１〜３により得られるフィルムは、二つのガラス転移温度を有し、且つ得られるフィルムは白濁したものであった。
【００７９】
【表１】

実施例１
合成例１により得られたＮ−メチルマレイミド・イソブテン共重合体６０重量％およびアクリロニトリル単位含量３０重量％のアクリロニトリル・スチレン共重合体４０重量％をドライブレンドした後、６５ｍｍφ２軸押出機（株式会社日本製鋼所製、商品名ＴＥＸ６５α）に供し、溶融混練の後、ペレタイズした。得られた樹脂組成物ペレットのガラス転移温度は１３０℃であった。
【００８０】
得られた樹脂組成物ペレットを図１で示すフィルム成形装置に投入した。その際のフィルム化条件は、Ｔダイ出口の溶融樹脂温度２６５℃、引き取り速度３０ｍ／分、第一冷却ロール表面温度１１０℃とし、幅約５００ｍｍ、厚み約１００μｍの光学フィルムとした。得られた光学フィルムの評価結果を表２に示す。
【００８１】
得られた光学フィルムは光学等方性および厚み精度に優れるものであった。
【００８２】
比較例１
合成例１で合成したＮ−メチルマレイミド・イソブテン共重合体８０重量％およびアクリロニトリル単位含量３０重量％のアクリロニトリル・スチレン共重合体２０重量％をドライブレンドした後、６５ｍｍφ２軸押出機（株式会社日本製鋼所製、商品名ＴＥＸ６５α）に供し、溶融混練の後、ペレタイズした。得られた樹脂組成物ペレットのガラス転移温度は１４０℃であった。
【００８３】
得られた樹脂組成物ペレットを図１で示すフィルム成形装置に投入した。その際のフィルム化条件は、Ｔダイ出口の溶融樹脂温度２７５℃、引き取り速度９ｍ／分、第一冷却ロール表面温度を１２０℃とし、幅約５００ｍｍ、厚み約１００μｍのフィルムとした。得られた光学フィルムの評価結果を表２に示す。
【００８４】
得られた光学フィルムは、比較的高い光学等方性を示すものであったが、引き取り速度が９ｍ／分と低いため、光学フィルムの生産性に劣るものであった。
【００８５】
比較例２
光学フィルムの引き取り速度を９ｍ／分の代わりに、３０ｍ／分とした以外は比較例１と同様の方法により光学フィルムの製造を行った。得られた光学フィルムの評価結果を表２に示す。
【００８６】
得られた光学フィルムは、大きな光学異方性が発現しているものであった。
【００８７】
比較例３
合成例１により得られたＮ−メチルマレイミド・イソブテン共重合体３０重量％およびアクリロニトリル単位含量３０重量％のアクリロニトリル・スチレン共重合体７０重量％をドライブレンドした後、６５ｍｍφ２軸押出機（株式会社日本製鋼所製、商品名ＴＥＸ６５α）に供し、溶融混練の後、ペレタイズした。得られた樹脂組成物ペレットのガラス転移温度は１１５℃と低い値であった。
【００８８】
得られた樹脂組成物ペレットを図１で示すフィルム成形装置に投入した。フィルム化条件は、Ｔダイ出口の溶融樹脂温度２６０℃、引き取り速度３０ｍ／分、第一冷却ロール表面温度１００℃とし、幅約５００ｍｍ、厚み約１００μｍのフィルムとした。得られたフィルムの評価結果を表２に示す。
【００８９】
得られたフィルムは光学異方性が高いものであった。
【００９０】
比較例４
フィルム成形装置のフィルム化条件の引き取り速度３０ｍ／分を引き取り速度１０５ｍ／分とした以外は、実施例１と同様の方法によりフィルムを得た。得られたフィルムの評価結果を表２に示す。
【００９１】
得られたフィルムは厚み精度が乏しいものであった。
【００９２】
比較例５
ポリカーボネート樹脂（帝人化成株式会社製、商品名パンライトＬ−１２０ＺＷ）を図１で示すフィルム成形装置に投入した。フィルム化条件は、Ｔダイ出口の溶融樹脂温度２８０℃、引き取り速度３０ｍ／分、第一冷却ロール表面温度１２５℃とし、幅約５００ｍｍ、厚み約１００μｍのフィルムとした。得られたフィルムの評価結果を表２に示す。
【００９３】
得られたフィルムは光学異方性が高いものであった。
【００９４】
【表２】

比較例６
フィルム成形装置のフィルム化条件の第一冷却ロール表面温度１１０℃を８５℃とした以外は、実施例１と同様の方法によりフィルムを得た。
【００９５】
得られたフィルムの表面には筋模様が多数認められ、光学用途としての品質を満たすものではなかった。
【００９６】
比較例７
フィルム成形装置のフィルム化条件の第一冷却ロール表面温度１１０℃を１５５℃とした以外は、実施例１と同様の方法によりフィルムを得た。
【００９７】
得られたフィルムの表面には筋模様が多数認められ、光学用途としての品質を満たすものではなかった。
【００９８】
実施例２
実施例１により得られた光学フィルムを１５ｃｍ四方角に裁断して２軸延伸試験装置（株式会社東洋精機製作所製）に設置し、フィルム引き取り方向に平行する方向に１軸延伸した。また、この１軸延伸では、延伸方向と直交するフィルム幅方向の長さが延伸前の長さに対して、延伸途中に変化しないよう幅拘束を行いつつ、１軸方向に延伸速度１５ｍｍ／分にて延伸温度１４５℃の条件で延伸倍率１．４倍に延伸した。得られた延伸光学フィルムの評価結果を表３に示す。
【００９９】
得られた延伸光学フィルムは光学等方性に優れたものであった。
【０１００】
実施例３
実施例１で得られた光学フィルムを１５ｃｍ四方角に裁断して２軸延伸試験装置に設置し、フィルム引き取り方向に平行する方向およびフィルム引き取り方向に直交する方向に２軸延伸した。また、この２軸延伸では、２軸方向同時に延伸速度１５ｍｍ／分にて延伸温度１４５℃の条件で延伸倍率１．３倍×１．３倍に延伸した。得られた延伸光学フィルムの評価結果を表３に示す。
【０１０１】
得られた延伸光学フィルムは光学等方性に優れたものであった。
【０１０２】
【表３】

【発明の効果】
以上から明らかなように、本発明により得られる光学フィルムは優れた光学等方性を有するため、ＬＣＤなどで使用される透明電極フィルム、偏光膜保護フィルム、位相差フィルムなどとして好適に用いることができ、本発明の製造方法によれば、優れた光学等方性を有する光学フィルムをＴダイ溶融押出法にて高い生産性で供給することが可能となる。
【図面の簡単な説明】
【図１】；本発明の製造方法に用いられる光学フィルム成形装置の一例。
【符号の説明】
１；二軸押出機
２；真空ベント
３；ダイバーターバルブ
４；ギアポンプ
５；スクリーンチェンジャー
６；Ｔダイ
７；第一冷却ロール
８；巻取りフィルム[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an optical film comprising a resin composition comprising a maleimide / olefin copolymer and an acrylonitrile / styrene copolymer, particularly an optical film having excellent optical isotropy.
[0002]
[Prior art]
2. Description of the Related Art In recent years, liquid crystal display devices (hereinafter, referred to as LCDs) have the advantages of low voltage, low power consumption, and light weight, and are used in portable devices, mobile communication devices, mobile mounted devices, personal computers, televisions, and home electric appliances. Widely used as display devices for products, audio products, industrial equipment, etc. LCDs are known as optical elements that sandwich liquid crystal molecules between two polarizing plates and perform black and white display using the optical filter function of the polarizing plates and the birefringence characteristics of the liquid crystal molecules. LCDs include a polarizing film and a polarizing film. Optical films such as a polarizing plate, a retardation film, a light diffusion film and a transparent electrode film made of a protective film (hereinafter referred to as a polarizing film protective film) are used. Among these optical films, the retardation film, the polarizing film protective film, and the transparent electrode film are present between the two polarizing plates, and thus, like the liquid crystal molecules described above, their optical characteristics greatly affect the display characteristics of the LCD. . Furthermore, among the optical films present between the two polarizing plates, the polarizing film protective film and the transparent electrode film are required to have no effect on the polarization state when polarized light passes through the film, and therefore, It is desired that the film is an optically isotropic film having a three-dimensionally uniform refractive index. That is, in addition to a small retardation in the film surface direction, an optical film having a small dependence on the incident angle of the retardation is desirable as the polarizing film protective film and the transparent electrode film.
[0003]
A transparent electrode film is a film in which a metal thin film or a semiconductor thin film such as ITO is formed on the surface of a polymer film by a method such as vacuum evaporation or sputtering. It is used instead of a glass transparent electrode substrate for the purpose of softening and the like. The polymer film, which is the base material of the transparent electrode film, is required to have high light transmittance, low haze, high optical isotropy, etc. as optical characteristics, and also have high heat resistance, high surface hardness, low gas permeability, In many cases, performance such as chemical resistance is required. Conventionally, a polymer film, which is a base material of a transparent electrode film, has a heat-resistant main-chain type aromatic film so that the dimensional change of the film does not occur due to heat when forming a semiconductor thin film such as a metal thin film or ITO. Films made of group-based polymers are mainly used, and typical examples include films made of polyethylene terephthalate (PET) and polycarbonate (PC). However, PET is likely to form crystals, and large birefringence due to the crystals is developed, so that it is difficult to obtain an optically isotropic film. On the other hand, although PC is amorphous, it has a benzene ring with large polarizability anisotropy in the molecule, so that the segment, which is a constituent unit of the molecular chain, shows large polarizability anisotropy, and the orientation complex during molding processing. Since refraction easily occurs, it is difficult to obtain an optically isotropic film. Also, a transparent conductive film based on a film composed of a main chain type aromatic polymer such as polyarylate (PAR) or polyether sulfone (PES) has been proposed, and these films are very excellent. Although it is known that it has heat resistance, PAR and PES have a problem that it is difficult to obtain an optically isotropic film because PAR and PES have a benzene ring in the molecule similarly to PC. In addition, the main chain type aromatic polymer as described above is an optically isotropic film formed by a molding method or a molding condition that suppresses the molecular orientation without giving a tension as much as possible during film formation. However, in reality, there are various problems as described below. For example, in the solution casting method, after a high-viscosity solution (dope) is cast on a supporting substrate, most of the solvent is removed by heating and peeled off from the supporting substrate as a self-supporting film. This is a film forming method of drying to remove the remaining solvent, and since no tension is applied to the film, a film having excellent optical isotropy can be obtained. In addition, a large-scale and expensive production facility is required, and the time required for drying the solvent is long, resulting in poor productivity and high film cost. In order to improve the productivity by the solution casting method, means for extending the drying step of the solvent and means for shortening the drying time of the solvent can be considered. When the solvent is expensive and the drying time of the solvent is shortened, the solvent tends to remain in the formed film, which may affect the environment. On the other hand, in a melt extrusion method using a T-die (hereinafter, referred to as a T-die melt extrusion method), a resin is melted in an extruder, the molten resin is extruded into a film shape from a slit of the T-die, and then rolls or air is blown. It is a molding method that draws while cooling by, for example, compared to the solution casting method, the manufacturing equipment is inexpensive and excellent in productivity, but tension is applied when the film is pulled, so it can be used with an optically isotropic film. To do this, the take-up speed must be made very slow, and there is a problem that high productivity, which is a feature of the T-die melt extrusion method, cannot be obtained.
[0004]
Even in the case of an optically isotropic film obtained by a forming method or a forming condition that suppresses the molecular orientation as described above, when stress is generated in the film by applying heat or deformation to the film, There is a problem that distortion or orientation occurs in the segment and optical anisotropy appears in the film. The easiness of the optical anisotropy with respect to the stress of the polymer can be expressed by the photoelastic coefficient. As the photoelastic coefficient increases, a large optical anisotropy develops with a small stress. It is generally known that an aromatic polymer has a large photoelastic coefficient.
[0005]
The polarizing film protective film is used for the purpose of protecting the polarizing film. As a polarizing film, a uniaxially stretched film in which iodine or a dye exhibiting dichroism is contained in a polyvinyl alcohol film is widely and generally used, but this polarizing film has low mechanical strength, such as water, heat, and ultraviolet light. Because of this, the polarization characteristics are liable to be deteriorated, so that it is usually used in LCDs as a laminate film in which a polarizing film protective film is adhered to both sides. Conventionally, a triacetyl cellulose (TAC) film is mainly used as a protective film for a polarizing film, and since a TAC film is formed by a solution casting method, it has excellent optical isotropy, surface smoothness, and thickness accuracy. It is known as a film having very few foreign matter defects. However, although the TAC film has a small phase difference in the plane direction, the phase difference has a large incident angle dependency, and thus there is a problem that the viewing characteristics are dependent on the display characteristics of the LCD. Further, since TAC has a large amount of change in phase difference with respect to stress, that is, a large photoelastic coefficient, it is necessary to pay close attention to heat and deformation that cause stress. Further, since the TAC film is formed by a solution casting method, large-scale and high-cost equipment is required, and it is difficult to form the film easily.
[0006]
A retardation film is a film used between two polarizing plates. Unlike a polarizing film protective film and a transparent electrode film, it has optical anisotropy like liquid crystal molecules and changes the polarization state of light. It is used to improve the display characteristics of the LCD, that is, the contrast and the viewing angle characteristics. A retardation film is obtained by uniaxially or biaxially stretching a raw film and molecularly orienting the film.However, since the retardation film requires very uniform optical characteristics, it is necessary to protect the polarizing film in an unstretched stage. Like the film and the transparent electrode film, excellent optical isotropy is required. Conventionally, a PC film has been mainly used as a retardation film. However, as described above, PC has a large photoelastic coefficient, so that optical anisotropy is easily developed, and high cost is required to obtain optical isotropy. In fact, the molding is performed by a simple solution casting method or a low-speed molding by a melt extrusion method. Further, since the phase difference of the PC film is easily changed by the stress, the phase difference is easily generated in a post-processing step such as punching or bonding, and the phase difference may be changed by the heat of the backlight of the LCD.
[0007]
Also disclosed is a transparent film comprising a composition consisting of 1 to 99% by weight of a maleimide / olefin copolymer and 99 to 1% by weight of an acrylonitrile / styrene copolymer containing 21 to 45% by weight of acrylonitrile units (for example, And Patent Document 1.).
[0008]
[Patent Document 1]
JP-A-2000-080240
[0009]
[Problems to be solved by the invention]
However, since the polymer film substrate used for the transparent electrode film needs to be a film having excellent optical isotropy, the film is a solution casting solution having a high production cost in order to suppress optical anisotropy. It is common to mold by the method, and even if melt extrusion is more advantageous than the solution casting method in terms of cost, the take-off speed is extremely slow to suppress the optical anisotropy and the molding is performed. It is common to do.
[0010]
In addition, the TAC film conventionally used as a polarizing film protective film is formed by a solution casting method which is expensive in manufacturing cost, and further, the film has poor three-dimensional optical isotropy, and the phase difference of the film is affected by stress. There is a problem that tends to change depending on.
[0011]
The transparent film described in Patent Literature 1 relates to a film characterized by being transparent to the last, and Patent Literature 1 does not study to find optical characteristics and the like.
[0012]
Therefore, an object of the present invention is to produce an optical film composed of a resin composition comprising a maleimide-olefin copolymer and a styrene-acrylonitrile copolymer having excellent three-dimensional optical isotropy by a T-die melt extrusion method. It is an object of the present invention to provide a method for producing by the nature.
[0013]
[Means for Solving the Problems]
The inventors of the present invention have eagerly attempted to overcome the problems of the prior art in which the optical isotropy decreases with an increase in the take-up speed in the T-die melt extrusion method, which is cost-effective over the solution casting method. As a result of repeated studies, a resin composition obtained by blending a maleimide-olefin copolymer and an acrylonitrile-styrene copolymer having a specific composition at a specific ratio is taken at a specific take-off speed by a T-die melt extrusion method. As a result, they have found that an optical film having excellent three-dimensional optical isotropy can be obtained with high production efficiency, and have completed the present invention.
[0014]
That is, the present invention is a copolymer comprising 40 to 60 mol% of a unit represented by the following general formula (I) and 60 to 40 mol% of a unit represented by the following general formula (II), and has a number average molecular weight of 1 × 10 ³ 5 × 10 or more ⁶ The following resin composition consisting of 70 to 40% by weight of a maleimide / olefin copolymer and 30 to 60% by weight of an acrylonitrile / styrene copolymer containing 21 to 45% by weight of an acrylonitrile unit is formed into a molten film by a T-die melt extrusion method. A method for producing an optical film, comprising: extruding, cooling the molten film with one or a plurality of cooling rolls, and taking the film at a take-up speed of 10 m / min to 100 m / min when producing the film.
[0015]
Embedded image

(R ¹ Represents hydrogen or an alkyl group having 1 to 6 carbon atoms. )
[0016]
Embedded image

(R ² , R ³ Each independently represents hydrogen or an alkyl group having 1 to 6 carbon atoms. )
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
[0018]
The production method of the present invention is, as a resin composition, a copolymer comprising 40 to 60 mol% of the unit represented by the general formula (I) and 60 to 40 mol% of the unit represented by the general formula (II). Having a number average molecular weight of 1 × 10 ³ 5 × 10 or more ⁶ The resin composition comprises a resin composition comprising the following maleimide / olefin copolymer (70 to 40% by weight) and acrylonitrile / styrene copolymer (30 to 60% by weight) containing acrylonitrile units (21 to 45% by weight).
[0019]
Where R ¹ Is hydrogen or an alkyl group having 1 to 6 carbon atoms, and examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an s-butyl group and a t-butyl group. And a pentyl group, a hexyl group, a cyclopropyl group, a cyclobutyl group, a cyclohexyl group, and the like. Among them, a methyl group is preferable because an optical film having particularly excellent heat resistance and moldability can be obtained. Also, R ² And R ³ Are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and examples of the alkyl group having 1 to 6 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, s-butyl, Examples thereof include a t-butyl group, a pentyl group, a hexyl group, a cyclopropyl group, a cyclobutyl group, and a cyclohexyl group. Among them, a methyl group is preferable because an optical film excellent in heat resistance and moldability is obtained. Is preferred.
[0020]
Such a maleimide / olefin copolymer can be obtained, for example, by a radical copolymerization reaction between maleimides and olefins. At this time, as the compound for deriving the unit represented by the general formula (I), for example, maleimide, N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, Ni-propylmaleimide, Nn- Maleimides such as butylmaleimide, Ni-butylmaleimide, Nt-butylmaleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, N-cyclopropylmaleimide, N-cyclobutylmaleimide and N-cyclohexylmaleimide And N-methylmaleimide is particularly preferred since an optical film having excellent heat resistance, mechanical properties, and transparency can be obtained. Furthermore, these compounds can be used alone or in combination of two or more.
[0021]
Examples of the compound for deriving the unit represented by the general formula (II) include olefins such as isobutene, 2-methyl-1-butene, 2-methyl-1-pentene, and 2-methyl-1-hexene. Of these, isobutene is particularly preferable because an optical film having excellent heat resistance, mechanical properties, and transparency can be obtained. These compounds can be used alone or in combination of two or more.
[0022]
The unit represented by the general formula (I) in the maleimide / olefin copolymer is from 40 to 60 mol%, and particularly preferably from 45 to 55 mol%, since it becomes an optical film having excellent heat resistance and mechanical properties. . Here, when the unit represented by the general formula (I) exceeds 60 mol%, the obtained optical film becomes brittle. On the other hand, when it is less than 40 mol%, the heat resistance of the obtained optical film is reduced.
[0023]
Further, the maleimide / olefin copolymer may contain a unit derived from another monomer component as needed without impairing the object of the present invention. For example, styrene derivatives such as styrene and α-methylstyrene; methacrylic acid such as methacrylic acid, methyl methacrylate and ethyl methacrylate or esters thereof; acrylic acid such as acrylic acid, methyl acrylate and ethyl acrylate or esters thereof Vinyl esters such as vinyl acetate and vinyl benzoate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, propiovinyl ether and butyl vinyl ether; maleic anhydride; and one or more compounds selected from acrylonitrile. Less than 5 mol% Rukoto is preferable.
[0024]
The maleimide-olefin copolymer may be any of known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, precipitation polymerization, and emulsion polymerization, among which transparency, color tone, and the like. It is preferable that the film is obtained by a precipitation polymerization method, since an optical film having excellent properties can be obtained.
[0025]
As the polymerization initiator used in the polymerization reaction, for example, benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, dicumyl peroxide, Organic peroxides such as t-butylperoxyacetate and t-butylperoxybenzoate; 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-butyronitrile), And azo-based initiators such as 2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, and 1,1'-azobis (cyclohexane-1-carbonitrile).
[0026]
Solvents used in the solution polymerization method and the precipitation polymerization method include, for example, aromatic solvents such as benzene, toluene and xylene; alcohol solvents such as methanol, ethanol, propyl alcohol and butyl alcohol; cyclohexane, dioxane, tetrahydrofuran, acetone and methyl ethyl ketone Dimethylformamide, isopropyl acetate, and a mixed solvent of an aromatic solvent and an alcohol solvent.
[0027]
The polymerization temperature at that time can be appropriately set according to the decomposition temperature of the initiator, but is generally preferably in the range of 40 to 150 ° C.
[0028]
The maleimide / olefin copolymer can also be obtained by post-imidization of the maleic anhydride / olefin copolymer using ammonia and / or an alkylamine as an alternative method.
[0029]
In such a post-imidization reaction, for example, a maleic anhydride / olefin copolymer is converted into an alcohol solvent such as methanol, ethanol, or propanol; an aromatic solvent such as benzene or toluene; an ester solvent such as ethyl acetate or isopropyl acetate; A method in which an amidation reaction and an imidation reaction are continuously performed by dissolving or dispersing in a mixed solvent of an aromatic solvent and an alcohol solvent or the like and reacting with ammonia and / or an alkylamine at a temperature of 50 to 250 ° C; After reacting with ammonia and / or an alkylamine to obtain an amide, the amide can be heated to cause dehydration ring closure and imidation, or the like.
[0030]
The maleimide-olefin copolymer used in the present invention has a number average molecular weight (Mn) of 1 × 10 ³ 5 × 10 or more ⁶ 1 × 10 ⁴ 5 × 10 or more ⁵ The following is preferred. Number average molecular weight is 5 × 10 ⁶ If it exceeds 3, the melt viscosity of the maleimide / olefin copolymer becomes too high, and the fluidity of the resin in T-die melt extrusion becomes poor, resulting in an optical film having poor thickness accuracy and surface smoothness. On the other hand, the number average molecular weight is 1 × 10 ³ If it is less than 1, the mechanical strength of the obtained optical film becomes poor. Here, the number average molecular weight in the present invention is a standard polystyrene conversion value determined by gel permeation chromatography (GPC).
[0031]
The acrylonitrile / styrene copolymer used in the present invention is an acrylonitrile / styrene copolymer containing 21 to 45% by weight of acrylonitrile units. Here, when the acrylonitrile unit is less than 21% by weight or more than 45% by weight, the compatibility between the maleimide / olefin copolymer and the acrylonitrile / styrene copolymer decreases, and the obtained film becomes opaque. In addition, heat resistance also decreases.
[0032]
The mixing ratio of the maleimide / olefin copolymer and the acrylonitrile / styrene copolymer in the present invention is 70 to 40% by weight of the maleimide / olefin copolymer and 30 to 60% by weight of the acrylonitrile / styrene copolymer. From the viewpoint of obtaining an optical film having an excellent balance of heat resistance and optical properties, it is preferable that the content of the maleimide / olefin copolymer is 70 to 50% by weight and the amount of the acrylonitrile / styrene copolymer is 30 to 50% by weight. When the amount of the maleimide / olefin copolymer is less than 40% by weight, the heat resistance and the optical isotropy of the film become poor, which is not preferable. When the amount of the maleimide / olefin copolymer exceeds 70% by weight, the film Is not preferred because of poor optical isotropy.
[0033]
The optical isotropy of the film referred to in the present invention refers to the homogeneity of the three-dimensional refractive index. In the case of an ideal film having the highest optical isotropy, the refractive index is uniform in all directions of the film. Become. In addition, in order to quantify the optical isotropy, a phase difference in a film plane and in a thickness direction is generally used. Retardation is defined as the product of birefringence and optical path length, and birefringence is defined as the difference between the refractive index in a particular direction and the refractive index in a direction perpendicular to that direction. Therefore, a film having a small value even when the phase difference is measured along any direction has excellent optical isotropy.
[0034]
The production method of the present invention relates to a method for producing an optical film having excellent optical isotropy. The obtained optical film has a retardation in the film surface direction of 10 nm or less and a retardation in the thickness direction of 50 nm. The following optical films are preferable. The smaller the retardation, the more preferable the optical film obtained by the present invention.
[0035]
In the production method of the present invention, when the above resin composition is extruded as a molten film by a T-die melt extrusion method and cooled by one or more cooling rolls to produce a film, a take-up speed of 10 m / min to 100 m / m The present invention relates to a method for producing an optical film, characterized in that the film is taken in the range of minutes, and an example of a film producing apparatus that can be used for producing the optical film of the present invention is shown in FIG. The present invention is not limited by this manufacturing apparatus, and may be an apparatus or the like to which an additional apparatus or the like is added.
[0036]
Here, reference numerals in FIG. 1 are as follows: 1: twin screw extruder, 2: vacuum vent, 3: diverter valve, 4: gear pump, 5: screen changer, 6: T die, 7: first cooling. Roll, 8: roll-up film.
[0037]
The T-die melt extrusion method referred to in the present invention is a method for producing a film characterized in that a resin melt-kneaded in an extruder is extruded from a T-die into a film, and the molten film is taken out while being cooled by a cooling roll. . Here, in the T-die melt extrusion method, it is common that tension is applied to the film when the melted film is taken out, and the resulting film is liable to cause birefringence due to molecular orientation. When producing an optical film having excellent optical isotropy, it is necessary to apply the film at a low speed of, for example, less than 10 m / min so as not to apply tension to the film as much as possible and to prevent birefringence due to molecular orientation. Met. That is, although the T-die melt extrusion method is widely known as a method capable of producing a film having a high surface smoothness with high productivity, it is necessary to produce an optical film having excellent optical isotropy. The fact is that the features are not fully utilized.
[0038]
On the other hand, the method for producing an optical film of the present invention is characterized in that the optical film is taken up at a high speed of 10 m / min to 100 m / min by a T-die melt extrusion method, thereby producing an optical film having excellent optical isotropy. It can be manufactured by the nature. The film take-up speed is not particularly limited as long as it is within the above range, and the thickness accuracy tends to decrease due to an increase in the take-up speed. Good.
[0039]
In addition, in the T-die melt extrusion method, in addition to the above-mentioned take-up speed, the molding conditions that affect the film properties include the temperature of the molten resin, the surface temperature of the cooling roll, and especially the T-die side when there are a plurality of cooling rolls. Surface temperature of the first cooling roll located at the most upstream position of the first cooling roll. In the production method of the present invention, the temperature of the molten resin may be appropriately selected depending on the discharge amount, the thickness, and the like, and among them, in order to avoid deterioration in film appearance due to thermal decomposition of the molten resin, the resin is melted. It is preferable to maintain the temperature from 300 ° C. or lower until discharge from the T-die, particularly preferably 290 ° C. or lower.
[0040]
The temperature of the chill roll, particularly the temperature setting of the first chill roll, is one of the important manufacturing conditions that greatly affects the appearance and optical characteristics of the obtained optical film. It is optimized in consideration of the releasability balance, in the production method of the present invention, the adhesion of the molten film to the cooling roll is sufficiently maintained, the occurrence of streaks on the film surface is suppressed, Since an optical film having a uniform thickness was obtained, the surface temperature of the cooling roll, particularly the surface temperature of the first cooling roll, was measured by a differential scanning calorimeter (hereinafter, referred to as DSC) at a heating rate of 10 ° C./min. The glass transition temperature of the resin composition is preferably −40 ° C. to glass transition temperature + 20 ° C., and particularly the glass transition temperature of the resin composition −35 ° C. to the glass transition temperature of the resin composition. It is preferable that the 10 ° C..
[0041]
The molding conditions other than those described above in the T-die melt extrusion method in the present invention include a screw rotation speed, a discharge amount, and the like. These conditions may be appropriately selected according to the film thickness, the take-up speed, and the like. Further, in order to suppress thermal decomposition and yellowing due to oxidation of the molten resin, it is preferable that the inside of the hopper, the cylinder of the extruder and the like be purged with nitrogen or evacuated.
[0042]
Hereinafter, an example of a molding apparatus and an additional molding apparatus for performing the manufacturing method of the present invention will be described, but the present invention is not limited to these.
[0043]
Typical examples of the extruder that can be used in the present invention include a single-screw extruder, a co-rotating twin-screw extruder, a different-rotating twin-screw extruder, and a tandem-type extruder. If volatile components such as water are contained in the resin composition provided for molding, the film appearance is deteriorated at the time of optical film extrusion, so these extruders are equipped with a vacuum vent and a hopper for removing volatile components. A device provided with a dryer or the like is appropriately used. In addition, the cylinder diameter, L / D, compression ratio, and screw design may be generally optimized according to production speed, film dimensions, and the like. Particularly, in the production of an optical film, the discharge speed is stabilized. At the same time, it may be optimized for the purpose of suppressing frictional heat generation and maintaining the resin temperature at or below the decomposition temperature.
[0044]
In the production method of the present invention, in order to stabilize the discharge speed and improve the thickness accuracy in the flow direction of the optical film, it is preferable to use a gear pump having a pressure increasing function and a metering function in combination with the extruder. Further, when a foreign substance is filtered by passing a molten resin through a filter system to be described later, or when the pressure loss in the container exceeds the extrusion pressure of the extruder, the pressure needs to be increased by a gear pump. However, since the molten resin may stay in the gear pump and may be thermally decomposed or yellowed, a structure that can prevent the stay is desirable.
[0045]
Also, for the purpose of removing foreign substances typified by agglomerates such as fibers, metals, sand, resin or additives contained in the molten resin, and for the purpose of removing resin degradation products generated in an extruder or a gear pump, It is preferable to install a filter in the T-die melt extrusion step, and such a filter may be a filter that filters foreign substances by using a single layer of a wire mesh made of an alloy such as stainless steel generally called a screen mesh. Particularly, in the case of manufacturing an optical film, since the requirements for the appearance of the film are very strict, there is a case where the foreign matter cannot be completely removed by the filtration using the screen mesh. In such a case, a wire mesh made of an alloy of the above stainless steel or the like is laminated, and a filter obtained by sintering each layer, a filter obtained by sintering a contact between fibers by a wire mesh intricately woven with fine fibers of stainless steel, a metal It is preferable to use a filter obtained by sintering the powder (hereinafter, these are collectively referred to as a sintered metal filter), and the sintered metal filter has high filtration efficiency and low filtration resistance with respect to the screen mesh. It is generally known that they can be obtained. The sintered metal filter is disclosed in, for example, JP-A-07-124426, JP-A-08-10521, JP-A-10-337415, and JP-A-11-76721. Further, a method of filtering a foreign substance by passing a molten resin through a filter system in which a large number of sintered metal filters are incorporated in a container in the form of a tube or a disk is disclosed in, for example, JP-A-08-10522. Since a higher filtration efficiency and lower filtration resistance can be obtained than using a sintered metal filter alone, it can be suitably used in the production method of the present invention. However, since the molten resin may be thermally decomposed or yellowed in the filter system, it is necessary to pay attention to the residence time in the filter system, and the filter system is unlikely to stay in dead space etc. It is desirable that the structure be simple.
[0046]
In the production method of the present invention, since the molten resin is formed into a wide film in the T-die, the dimensions of the film are mainly determined by the T-die. The flow path in the T-die may be optimized according to the viscoelastic properties of the molten resin, and the dies generally include a straight manifold type, a coat hanger type, a fish tail type, and a coat hanger manifold type. In particular, when importance is attached to the thickness accuracy of the obtained optical film, it is preferable to use a manifold type die. Adjustment of the gap of the lip, which is the outlet of the molten resin, is one of the important factors that determine the thickness accuracy of the film.
[0047]
The optical film obtained by the production method of the present invention has a very strict thickness accuracy requirement. One of the reasons is that the above-mentioned phase difference is defined by the product of the birefringence of the medium through which light passes and the optical path length. Therefore, even if the birefringence is uniform, if the film thickness is non-uniform, the phase difference becomes non-uniform, and the optical isotropy of the film becomes poor. However, the precise thickness adjustment of the lip requires time even for skilled personnel, so in recent years an automatic thickness control system using a computer has been introduced to improve not only the film thickness accuracy but also the yield. It has greatly contributed. As such a method, there is a method of measuring the thickness of the film online and automatically adjusting the gap of the lip or adjusting the speed of the gear pump based on the result, for example, Japanese Patent Application Laid-Open No. 10-58518, Japanese Patent Laid-Open No. 2000-127226 discloses a method for automatically adjusting a lip, for example, a heat bolt method, a robot method, a lip heater method, a piezoelectric element method, and the like. The method can additionally be used.
[0048]
In addition, since the lip of the T-die is an exit portion of the molten resin, if the lip portion in contact with the molten resin has irregularities, the irregularities are transferred to the surface of the optical film, and the shape is solidified by the cooling roll. It becomes a die line. Therefore, it is desirable to reduce the surface roughness of the lip, particularly in contact with the molten resin, by a method such as electrolytic polishing. Furthermore, even if the surface roughness of the lip portion is small, if the thermally decomposed resin adheres to the lip portion to form a so-called eye, unevenness is generated on the surface of the lip, which causes a die line. It is important to prevent the molten resin from adhering to the lips in order to prevent the eyes from being noticed. In the production method of the present invention, lips coated with chromium or ceramic can be suitably used. In addition, since the resin tends to stay at the edge of the lip that comes into contact with the molten resin, the edge of the lip is preferably made as sharp as possible, particularly preferably 0.1 mmR or less.
[0049]
In the production method of the present invention, the molten resin (molten film) extruded from the slit of the T-die is brought into close contact with a cooling roll and cooled. Such a cooling roll, and the first cooling roll when there are a plurality of such rolls, are generally called a cast roll or a casting roll. Then, it is desired that the surface of the first cooling roll with which the molten film comes into contact has small surface roughness for the same reason as the lip of the T-die. Further, when there are a plurality of cooling rolls, it is important to keep the rotation speed of the first cooling roll and other cooling rolls constant, and if the rotation speed is uneven, a stripe in the width direction is formed on the film surface. May occur.
[0050]
And in order to cool the obtained optical film more efficiently, it is preferable to use a method of cooling the optical film wound around the first cooling roll from the opposite surface of the first cooling roll, such a method. Examples thereof include an air chamber method, a touch roll method, an air knife method, a rubber roll method, a cooling drum method, an ear pressing roll method, and an electrostatic peening method. Further, as a touch roll method, for example, a touch roll capable of elastic deformation has been proposed in JP-A-2002-36332, JP-A-WO97 / 28950, and JP-A-11-235747. A thinner film can be formed than using a rigid touch roll, and these methods can be employed in the present invention. Also, by suppressing the film from the opposite surface of the first cooling roll with a touch roll, there is an effect of flattening the surface roughness or making the molecular orientation in the take-up direction difficult to occur, so these touch rolls are preferably used. Can be. Of course, the cooling from the opposite surface of the first cooling roll is not particularly performed, and may be allowed to cool.
[0051]
Since the surface temperature of the cooling roll greatly affects the appearance of the obtained optical film, it is desirable to control the surface temperature of the cooling roll with an accuracy of 0.1 ° C. In this case, the resin temperature measured by DSC as described above is used. The glass transition temperature of the composition is preferably set to −40 ° C. to + 20 ° C., in which case pressurized water or oil is used as a medium for controlling the roll temperature. Note that oil temperature control is preferable because the temperature control accuracy is excellent.
[0052]
A slitter for cutting both ends of the obtained optical film may be provided, and the slitter at that time is not limited. Among them, the optical film obtained by the present invention is relatively hard, so that it is easy to suppress the occurrence of fine cracks in the fractured surface of the film. It is preferable to use a slitter called “slitter”.
[0053]
Further, in order to prevent foreign matter such as fibers from adhering to the surface of the obtained optical film, it is preferable to perform a masking treatment on one side or both sides of the film, and it is preferable to add an apparatus for performing a masking treatment.
[0054]
There is no particular limitation on a winding machine for winding the obtained optical film, and among them, it is preferable to use an accumulator for adjusting the balance between the take-up speed and the take-up speed.
[0055]
The optical film obtained by the production method of the present invention may be an optical film stretched for the purpose of improving mechanical strength, adjusting optical properties, and the like. May be added. The stretching process includes a process of continuously performing the process in the T-die melt extrusion process, a process of once winding the optical film, and then subjecting the film to a stretching device to stretch. Further, the stretching direction is selected depending on the purpose, uniaxial direction or biaxial direction is selected, and when stretching in the uniaxial direction, the length in the film width direction is constrained not to change in the middle of stretching with respect to the length before stretching. Is more preferable for obtaining a stretched film having uniform optical characteristics. Examples of the uniaxial stretching method include a method of stretching with a tenter, a method of stretching by rolling with a calendar, a method of stretching between rolls, and the like.A method of stretching with a tenter as the biaxial stretching method, a method of expanding in a tube shape and stretching. and so on.
[0056]
When the optical film obtained by the present invention is made into a stretched optical film, the stretching conditions are as follows. Since the film does not easily have uneven thickness and the obtained film has excellent mechanical properties and optical properties, it is measured by DSC. It is particularly preferable that the film is stretched in a stretching ratio of 1.1 to 3 times under a stretching temperature condition of 1 ° C. to 40 ° C. higher than the glass transition temperature of the obtained resin composition.
[0057]
The optical film obtained by the present invention may contain an additive within a range not exceeding the gist of the invention. As an adding method, a method of adding in a step of producing a resin composition, a T-die melt extrusion step, A method in which the resin composition and the additive are dry-blended, supplied to a hopper, and melt-kneaded in an extruder may be used.
[0058]
Examples of the additives include a surfactant, a polymer electrolyte, a conductive complex, an inorganic filler, a pigment, a dye, an antioxidant, a hindered amine light stabilizer, an ultraviolet absorber, an antistatic agent, an antiblocking agent, and a lubricant. And the like, and details thereof will be shown below, but the present invention is not limited thereto.
[0059]
Examples of the antioxidant include a hindered phenol-based antioxidant, a phosphorus-based antioxidant, and other antioxidants.These antioxidants may be used alone or in combination. good. And, since the antioxidant action is synergistically improved, it is preferable to use a hindered phenol-based antioxidant and a phosphorus-based antioxidant in combination, in which case, for example, 100 parts by weight of the hindered phenol-based antioxidant It is particularly preferable to use a mixture of 100 to 500 parts by weight of a phosphorus-based antioxidant. In addition, the amount of the antioxidant to be added is generally preferably from 0.001 to 2 parts by weight, particularly preferably from 0.01 to 1 part by weight, based on 100 parts by weight of the resin composition.
[0060]
Examples of hindered phenolic antioxidants include pentaerythritol-tetrakis (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate) and thiodiethylene-bis (3- (3,5-di -T-butyl-4-hydroxyphenyl) propionate), octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexane-1,6-diylbis (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionamide), diethyl ((3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl) methyl) phosphate, 3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-t-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol, ethyl Bis (oxyethylene) bis (3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate), hexamethylene-bis (3- (3,5-di-tert-butyl-4-hydroxyphenyl) Propionate), 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione, 1,3,5-tris ((4-t-butyl-3-hydroxy-2,6-xylyl) methyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione , 2,6-di-t-butyl-4- (4,6-bis (octylthio) -1,3,5-triazin-2-ylamino) phenol, 3,9-bis (2- (3- (3 -T-butyl-4-hydroxy-5-methylphenyl) Ropioniruokishi) -1,1-dimethylethyl) -2,4,8,10-spiro (5,5) undecane.
[0061]
Examples of the phosphorus-based antioxidant include tris (2,4-di-t-butylphenyl) phosphite and bis (2,4-bis (1,1-dimethylethyl) -6-methylphenyl) ethyl ester Acid, tetrakis (2,4-di-t-butylphenyl) (1,1-biphenyl) -4,4′-diylbisphosphonite, bis (2,4-di-t-butylphenyl) pentaerythritol di Phosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol-diphosphite, tetrakis (2,4-t-butyl) Phenyl) (1,1-biphenyl) -4,4′-diylbisphosphonite, di-t-butyl-m-cresyl-phosphonite, and the like. It is.
[0062]
Further, a hindered amine-based light stabilizer can be used, and the hindered amine-based light stabilizer has a molecular weight of preferably 1,000 or more, particularly preferably 1,500 or more, because it is excellent in an effect of suppressing thermal coloring. . Further, the addition amount of the hindered amine light stabilizer is preferably 0.01 part by weight to 1.5 parts by weight based on 100 parts by weight of the resin composition because the heat coloring prevention effect and the light stabilization effect are excellent. In particular, the amount is preferably 0.05 to 1.0 part by weight, and more preferably 0.1 to 0.5 part by weight.
[0063]
Such hindered amine light stabilizers include, for example, poly ((6-morpholino-s-triazine-2,4-diyl) ((2,2,6,6-tetramethyl-4-piperidyl) imino) hexamethylene ((2,2,6,6-tetramethyl-4-piperidyl) imino)) (molecular weight 1,600), poly ((6- (1,1,3,3-tetramethylbutyl) amino-1,3 , 5-Triazine-2,4-diyl) ((2,2,6,6-tetramethyl-4-piperidyl) imino) hexamethylene ((2,2,6,6-tetramethyl-4-piperidyl) imino )) (Molecular weight 2,000-3,100), dibutylamine-1,3,5-triazine-N, N′-bis (2,2,6,6-tetramethyl-4-piperidyl-1,6- Hexamethylenediamine-N- ( Polycondensate of 2,2,6,6-tetramethyl-4-piperidyl) butylamine (molecular weight: 2,600-3,400), N, N'-bis (3-aminopropyl) ethylenediamine-2,4-bis (N-butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino) -6-chloro-1,3,5-triazine condensate (molecular weight 2,000 or more), succinic acid Dimethyl-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine condensate (molecular weight: 3,100 to 4,000) and the like, and one or more of these are used be able to.
[0064]
As the ultraviolet absorber, for example, an ultraviolet absorber such as benzotriazole, benzophenone, triazine, and benzoate can be added as needed.
[0065]
In the production method of the present invention, a lubricant may be added for the purpose of suppressing frictional heat generation during T-die melt extrusion, improving extrusion stability, and the like, and the amount of the lubricant to be added is preferably 1 to 10000 ppm, particularly The content is preferably 5 to 2000 ppm, more preferably 10 to 500 ppm. Examples of such lubricants include aliphatic hydrocarbon lubricants such as liquid paraffin, natural paraffin, and polyethylene wax; higher aliphatic alcohols and higher fatty acid lubricants such as cetyl alcohol, stearyl alcohol, and stearic acid; stearamide; Aliphatic amide lubricants such as oleic amide, palmitic amide and methylene bis-stearamide; metal soap lubricants such as calcium stearate, zinc stearate, magnesium stearate and barium stearate; butyl stearate, ethylene glycol stearate And the like; fatty acid ester-based lubricants; composite lubricants and the like.
[0066]
The optical film obtained by the present invention is preferably a film having a light transmittance of 85% or more and a haze of 2% or less, since the film is excellent as a film used as an optical component. The thickness of the optical film is preferably from 10 to 300 μm, particularly preferably from 10 to 200 μm, because the film has excellent thickness accuracy, mechanical properties, and appearance.
[0067]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.
[0068]
Various physical properties shown in the examples were measured by the following methods.
[0069]
~ Number average molecular weight ~
The value was determined as a standard polystyrene equivalent value by an elution curve of a maleimide / olefin copolymer measured using gel permeation chromatography (GPC) (trade name: HLC-802A, manufactured by Tosoh Corporation).
[0070]
-Composition ratio of maleimide-olefin copolymer, acrylonitrile-styrene copolymer-
Elemental analysis, ¹ It was determined by 1 H-NMR measurement.
[0071]
~ Glass transition temperature of maleimide / olefin copolymer ~
The measurement was performed at a heating rate of 10 ° C./min using a differential scanning calorimeter (trade name: DSC200, manufactured by Seiko Instruments Inc.).
[0072]
~ Total light transmittance of optical film ~
It measured based on JIS-K-7105.
[0073]
~ Retardation of optical film ~
Using a fully automatic birefringence meter (manufactured by Oji Scientific Instruments Co., Ltd., trade name KOBRA-21ADH), based on the three-dimensional refractive index measured at a measurement wavelength of 590 nm, the phase difference and thickness in the film surface direction are obtained from the following equations. The phase difference in the direction was determined.
[0074]
Phase difference (R) in the film plane direction = (Nx-Ny) d
(Here, Nx: the refractive index in the slow axis direction in the film plane, Ny: the refractive index in the direction perpendicular to the slow axis direction in the film plane, d: film thickness.)
Phase difference (K) in film thickness direction = ((Nx + Ny) / 2-Nz) d
(Where, Nx: refractive index in the slow axis direction in the film plane, Ny: refractive index in the direction orthogonal to the slow axis direction in the film plane, Nz: refractive index in the normal direction of the film surface, d: Film thickness.)
~ Thickness of optical film ~
The center of the optical film was measured using a dial gauge (trade name: ID-C125B, manufactured by Mitutoyo Corporation).
[0075]
~ Optical film thickness unevenness ~
The thickness of the portion located 15 mm from the center and the end of the optical film was measured, and the difference in thickness between the two points was regarded as the thickness unevenness.
[0076]
Synthesis Example 1 (Synthesis of maleimide / olefin copolymer)
In a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a thermometer, and a degassing tube, 0.67 parts by weight of t-butyl peroxyneodecanoate and a mixed solvent of toluene and methanol (100 parts by weight of N-methylmaleimide) were added. : 1 part by weight), and after purging with nitrogen several times, 400 parts by weight of isobutene was charged and reacted at 60 ° C for 6 hours. The obtained particles were dried after centrifugation. From the results of elemental analysis of the obtained polymer (C: 64.7% by weight, H: 7.8% by weight, N: 8.4% by weight), the N-methylmaleimide unit and the isobutene unit in the produced polymer were respectively It was 50 mol%. The number average molecular weight (Mn) of the obtained polymer was 90,000.
[0077]
Reference Examples 1-2, Comparative Comparative Examples 1-3
According to Synthesis Example 1, the N-methylmaleimide / isobutene copolymer and the acrylonitrile / styrene copolymer having different acrylonitrile contents shown in Table 1 were dry-blended at a weight ratio of 50:50, and a 30 mmφ twin screw extruder (Japan Co., Ltd.) After being melt-kneaded, the mixture was extruded at 230 ° C to 250 ° C and pelletized. The obtained resin composition pellets were hot-pressed at 220 ° C. for 5 minutes to form a film having a thickness of 100 μm. Table 1 shows the measurement results of the physical properties of the film.
[0078]
As is clear from these results, the films obtained in Reference Examples 1 and 2 show a single glass transition temperature and show excellent light transmittance. On the other hand, the films obtained in Reference Comparative Examples 1 to 3 using the acrylonitrile-styrene copolymer having a small amount or a large amount of the acrylonitrile content had two glass transition temperatures, and the obtained film was cloudy. .
[0079]
[Table 1]

Example 1
After dry blending 60% by weight of the N-methylmaleimide / isobutene copolymer obtained in Synthesis Example 1 and 40% by weight of the acrylonitrile / styrene copolymer having an acrylonitrile unit content of 30% by weight, a 65 mmφ twin screw extruder (Japan Co., Ltd.) The product was subjected to melt kneading and then pelletized. The glass transition temperature of the obtained resin composition pellets was 130 ° C.
[0080]
The obtained resin composition pellets were put into a film forming apparatus shown in FIG. Filming conditions at this time were an optical film having a width of about 500 mm and a thickness of about 100 μm, with a molten resin temperature of 265 ° C. at the exit of the T-die, a take-up speed of 30 m / min, a first cooling roll surface temperature of 110 ° C. Table 2 shows the evaluation results of the obtained optical films.
[0081]
The obtained optical film was excellent in optical isotropy and thickness accuracy.
[0082]
Comparative Example 1
After dry blending 80% by weight of the N-methylmaleimide / isobutene copolymer synthesized in Synthesis Example 1 and 20% by weight of the acrylonitrile / styrene copolymer having an acrylonitrile unit content of 30% by weight, a 65 mmφ twin screw extruder (Nippon Steel Corporation) (TEX65α), melt-kneaded, and pelletized. The glass transition temperature of the obtained resin composition pellets was 140 ° C.
[0083]
The obtained resin composition pellets were put into a film forming apparatus shown in FIG. The film forming conditions at that time were a molten resin temperature of 275 ° C. at the outlet of the T-die, a take-up speed of 9 m / min, a first cooling roll surface temperature of 120 ° C., and a film having a width of about 500 mm and a thickness of about 100 μm. Table 2 shows the evaluation results of the obtained optical films.
[0084]
Although the obtained optical film exhibited relatively high optical isotropy, the productivity of the optical film was poor because the take-off speed was as low as 9 m / min.
[0085]
Comparative Example 2
An optical film was manufactured in the same manner as in Comparative Example 1, except that the take-up speed of the optical film was changed to 30 m / min instead of 9 m / min. Table 2 shows the evaluation results of the obtained optical films.
[0086]
The obtained optical film exhibited large optical anisotropy.
[0087]
Comparative Example 3
After dry blending 30% by weight of the N-methylmaleimide / isobutene copolymer obtained in Synthesis Example 1 and 70% by weight of the acrylonitrile / styrene copolymer having an acrylonitrile unit content of 30% by weight, a 65 mmφ twin screw extruder (Japan Co., Ltd.) The product was subjected to melt kneading and then pelletized. The glass transition temperature of the obtained resin composition pellets was a low value of 115 ° C.
[0088]
The obtained resin composition pellets were put into a film forming apparatus shown in FIG. The film forming conditions were as follows: the temperature of the molten resin at the exit of the T-die was 260 ° C., the take-off speed was 30 m / min, the surface temperature of the first cooling roll was 100 ° C., and the film was about 500 mm wide and about 100 μm thick. Table 2 shows the evaluation results of the obtained films.
[0089]
The obtained film had high optical anisotropy.
[0090]
Comparative Example 4
A film was obtained in the same manner as in Example 1, except that the take-up speed of 30 m / min was changed to a take-up speed of 105 m / min. Table 2 shows the evaluation results of the obtained films.
[0091]
The resulting film had poor thickness accuracy.
[0092]
Comparative Example 5
A polycarbonate resin (trade name: Panlite L-120ZW, manufactured by Teijin Chemicals Limited) was charged into the film forming apparatus shown in FIG. The film forming conditions were as follows: the temperature of the molten resin at the exit of the T-die was 280 ° C., the take-up speed was 30 m / min, the surface temperature of the first cooling roll was 125 ° C., and the film was about 500 mm wide and about 100 μm thick. Table 2 shows the evaluation results of the obtained films.
[0093]
The obtained film had high optical anisotropy.
[0094]
[Table 2]

Comparative Example 6
A film was obtained in the same manner as in Example 1, except that the first cooling roll surface temperature 110 ° C. of the film forming conditions of the film forming apparatus was changed to 85 ° C.
[0095]
Many streaks were observed on the surface of the obtained film, and did not satisfy the quality for optical use.
[0096]
Comparative Example 7
A film was obtained in the same manner as in Example 1 except that the first cooling roll surface temperature 110 ° C. of the film forming conditions of the film forming apparatus was changed to 155 ° C.
[0097]
Many streaks were observed on the surface of the obtained film, and did not satisfy the quality for optical use.
[0098]
Example 2
The optical film obtained in Example 1 was cut into a square of 15 cm, set in a biaxial stretching test apparatus (manufactured by Toyo Seiki Seisaku-sho, Ltd.), and uniaxially stretched in a direction parallel to the film take-off direction. In this uniaxial stretching, the stretching speed in the uniaxial direction is 15 mm / min while the width is restricted so that the length in the film width direction orthogonal to the stretching direction does not change during stretching. At a stretching temperature of 145 ° C. at a stretching ratio of 1.4 times. Table 3 shows the evaluation results of the obtained stretched optical films.
[0099]
The obtained stretched optical film was excellent in optical isotropy.
[0100]
Example 3
The optical film obtained in Example 1 was cut into a square of 15 cm, set in a biaxial stretching test apparatus, and biaxially stretched in a direction parallel to the film take-off direction and a direction perpendicular to the film take-off direction. In this biaxial stretching, stretching was performed at a stretching rate of 1.3 × 1.3 at a stretching temperature of 145 ° C. at a stretching speed of 15 mm / min simultaneously in the biaxial directions. Table 3 shows the evaluation results of the obtained stretched optical films.
[0101]
The obtained stretched optical film was excellent in optical isotropy.
[0102]
[Table 3]

【The invention's effect】
As is clear from the above, since the optical film obtained by the present invention has excellent optical isotropy, it can be suitably used as a transparent electrode film, a polarizing film protective film, a retardation film and the like used in LCDs and the like. According to the production method of the present invention, an optical film having excellent optical isotropy can be supplied with high productivity by a T-die melt extrusion method.
[Brief description of the drawings]
FIG. 1 shows an example of an optical film forming apparatus used in the production method of the present invention.
[Explanation of symbols]
1: Twin screw extruder
2: vacuum vent
3: Divertor valve
4: Gear pump
5; screen changer
6; T die
7; first cooling roll
8; Winding film

Claims (2)

It is a copolymer consisting of 40 to 60 mol% of a unit represented by the following general formula (I) and 60 to 40 mol% of a unit represented by the following general formula (II), and has a number average molecular weight of 1 × 10 ³ or more and 5 × 10 ⁶ or less is maleimide-olefin copolymer 70-40 wt%, melt acrylonitrile units 21 to 45 wt% consisting of acrylonitrile-styrene copolymer 30 to 60 wt% comprising the resin composition by a T-die melt extrusion method A method for producing an optical film, comprising: extruding as a film, cooling the molten film with one or a plurality of cooling rolls to produce a film, and taking the film at a take-up speed of 10 m / min to 100 m / min.

(R ¹ represents hydrogen or an alkyl group having 1 to 6 carbon atoms.)

(R ² and R ³ each independently represent hydrogen or an alkyl group having 1 to 6 carbon atoms.) The glass transition temperature of the resin composition obtained by measuring the surface temperature of the first cooling roll installed at the most upstream position on the T-die side by a differential scanning calorimeter at a heating rate of 10 ° C./min. 2. The method for producing an optical film according to claim 1, wherein the molten film is cooled by setting the transition temperature in a range of + 20 ° C.

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