JP4892794B2 - Solid for preparing cellulose ester solution, cellulose ester solution, method for producing cellulose ester film, cellulose ester film, polarizing plate and display device using the same - Google Patents

Description

【０１３８】
式中、Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄及びＲ₅は同一でも異なってもよく、水素原子、ハロゲン原子、ニトロ基、ヒドロキシル基、アルキル基、アルケニル基、アリール基、アルコキシル基、アシルオキシ基、アリールオキシ基、アルキルチオ基、アリールチオ基、モノ若しくはジアルキルアミノ基、アシルアミノ基または５〜６員の複素環基を表し、Ｒ₄とＲ₅は閉環して５〜６員の炭素環を形成してもよい。
【０１３９】
また、上記記載のこれらの基は、任意の置換基を有していて良い。
以下に本発明に好ましく用いられる紫外線吸収剤の具体例を挙げるが、本発明はこれらに限定されない。
【０１４０】
ＵＶ−１：２−（２′−ヒドロキシ−５′−メチルフェニル）ベンゾトリアゾール
ＵＶ−２：２−（２′−ヒドロキシ−３′，５′−ジ−ｔｅｒｔ−ブチルフェニル）ベンゾトリアゾール
ＵＶ−３：２−（２′−ヒドロキシ−３′−ｔｅｒｔ−ブチル−５′−メチルフェニル）ベンゾトリアゾール
ＵＶ−４：２−（２′−ヒドロキシ−３′，５′−ジ−ｔｅｒｔ−ブチルフェニル）−５−クロロベンゾトリアゾール
ＵＶ−５：２−（２′−ヒドロキシ−３′−（３″，４″，５″，６″−テトラヒドロフタルイミドメチル）−５′−メチルフェニル）ベンゾトリアゾール
ＵＶ−６：２，２−メチレンビス（４−（１，１，３，３−テトラメチルブチル）−６−（２Ｈ−ベンゾトリアゾール−２−イル）フェノール）
ＵＶ−７：２−（２′−ヒドロキシ−３′−ｔｅｒｔ−ブチル−５′−メチルフェニル）−５−クロロベンゾトリアゾール
ＵＶ−８：２−（２Ｈ−ベンゾトリアゾール−２−イル）−６−（直鎖及び側鎖ドデシル）−４−メチルフェノール（ＴＩＮＵＶＩＮ１７１、Ｃｉｂａ製）
ＵＶ−９：オクチル−３−〔３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−（クロロ−２Ｈ−ベンゾトリアゾール−２−イル）フェニル〕プロピオネートと２−エチルヘキシル−３−〔３−ｔｅｒｔ−ブチル−４−ヒドロキシ−５−（５−クロロ−２Ｈ−ベンゾトリアゾール−２−イル）フェニル〕プロピオネートの混合物（ＴＩＮＵＶＩＮ１０９、Ｃｉｂａ製）
また、本発明に好ましく用いられる紫外線吸収剤のひとつであるベンゾフェノン系紫外線吸収剤としては下記一般式〔２〕で表される化合物が好ましく用いられる。
【０１４１】
【化２】

【０１４２】
式中、Ｙは水素原子、ハロゲン原子またはアルキル基、アルケニル基、アルコキシル基、及びフェニル基を表し、これらのアルキル基、アルケニル基及びフェニル基は置換基を有していてもよい。Ａは水素原子、アルキル基、アルケニル基、フェニル基、シクロアルキル基、アルキルカルボニル基、アルキルスルホニル基又は−ＣＯ（ＮＨ）_n-1−Ｄ基を表し、Ｄはアルキル基、アルケニル基又は置換基を有していてもよいフェニル基を表す。ｍ及びｎは１または２を表す。
【０１４３】
上記において、アルキル基としては、例えば、炭素数２４までの直鎖または分岐の脂肪族基を表し、アルコキシル基としては例えば、炭素数１８までのアルコキシル基で、アルケニル基としては例えば、炭素数１６までのアルケニル基で例えばアリル基、２−ブテニル基などを表す。又、アルキル基、アルケニル基、フェニル基への置換分としてはハロゲン原子、例えば、塩素原子、臭素原子、フッ素原子など、ヒドロキシル基、フェニル基（このフェニル基にはアルキル基又はハロゲン原子などを置換していてもよい）などが挙げられる。
【０１４４】
以下に一般式〔２〕で表されるベンゾフェノン系化合物の具体例を示すが、本発明はこれらに限定されない。
【０１４５】
ＵＶ−１０：２，４−ジヒドロキシベンゾフェノン
ＵＶ−１１：２，２′−ジヒドロキシ−４−メトキシベンゾフェノン
ＵＶ−１２：２−ヒドロキシ−４−メトキシ−５−スルホベンゾフェノン
ＵＶ−１３：ビス（２−メトキシ−４−ヒドロキシ−５−ベンゾイルフェニルメタン）
本発明で好ましく用いられる上記記載の紫外線吸収剤は、透明性が高く、偏光板や液晶素子の劣化を防ぐ効果に優れたベンゾトリアゾール系紫外線吸収剤やベンゾフェノン系紫外線吸収剤が好ましく、不要な着色がより少ないベンゾトリアゾール系紫外線吸収剤が特に好ましく用いられる。
【０１４６】
紫外線吸収剤添加液の添加方法としては、下記に記載の方法が挙げられる。
《添加方法Ａ》
紫外線吸収剤添加液の調製方法としては、アルコールやメチレンクロライド、ジオキソランなどの有機溶剤に紫外線吸収剤を溶解してから直接ドープ組成中に添加する。
【０１４７】
《添加方法Ｂ》
紫外線吸収剤添加液の調製方法としては、アルコールやメチレンクロライド、ジオキソランなどの有機溶剤に紫外線吸収剤と少量のセルロースエステル及び／又は本発明の固形物を溶解してからインラインミキサーでドープに添加する。
【０１４８】
本発明においては、添加方法Ｂの方が、紫外線吸収剤の添加量を容易に調整できるため、生産性に優れていて好ましい。
【０１４９】
紫外線吸収剤の使用量は化合物の種類、使用条件などにより一様ではないが、通常はセルロースエステルフィルム１ｍ²当り、０．２〜５．０ｇが好ましく、０．４〜２．０ｇがさらに好ましく、０．６〜１．０ｇが特に好ましい。
【０１５０】
また、本発明においては、特に、融点が２０℃以下の紫外線吸収剤が好ましく用いられる。
【０１５１】
一般的に紫外線吸収剤は溶解性に乏しいものが多いが、２５℃で液体である可塑剤が存在すると溶解しやすくなることが見いだされた。そのため、内部に２５℃で液体である可塑剤を含有する構成の場合、紫外線吸収剤を十分に添加し、余裕をもって溶解させることが可能となり、特に高い濃度のドープを調製する際に有効であり、特にまた、膜厚４５μｍ以下の膜厚で十分な紫外線吸収能を有するフィルムを提供することが可能となった。更に、２０℃で液体である紫外線吸収剤と２５℃で液体である可塑剤を内部に含ませることによって、より高い濃度の紫外線吸収剤と可塑剤を含有させることができ、フィルムに優れた透湿性と紫外線吸収能を付与することが可能となり、しかも、これらの添加物の析出による工程汚染も少なくなるという効果も得られた。
【０１５２】
このほか、特開平６−１４８４３０号、特願平１２−１５６０３９号に記載の高分子紫外線吸収剤も好ましく用いることができる。
【０１５３】
本発明の微粒子について説明する。
本発明の微粒子としては、無機化合物の微粒子または有機化合物の微粒子が挙げられる。
【０１５４】
無機化合物としては、珪素を含む化合物、二酸化珪素、酸化アルミニウム、酸化ジルコニウム、炭酸カルシウム、タルク、クレイ、焼成カオリン、焼成ケイ酸カルシウム、水和ケイ酸カルシウム、ケイ酸アルミニウム、ケイ酸マグネシウム及びリン酸カルシウム等が好ましく、更に好ましくは、ケイ素を含む無機化合物や酸化ジルコニウムであるが、セルロースエステルフィルムの濁度を低減できるので、二酸化珪素が特に好ましく用いられる。
【０１５５】
二酸化珪素の微粒子としては、例えば、アエロジルＲ９７２、Ｒ９７２Ｖ、Ｒ９７４、Ｒ８１２、２００、２００Ｖ、３００、Ｒ２０２、ＯＸ５０、ＴＴ６００（以上日本アエロジル（株）製）等の市販品が使用できる。
【０１５６】
酸化ジルコニウムの微粒子としては、例えば、アエロジルＲ９７６及びＲ８１１（以上日本アエロジル（株）製）等の市販品が使用できる。
【０１５７】
有機化合物としては、例えば、シリコーン樹脂、弗素樹脂及びアクリル樹脂等のポリマーが好ましく、中でも、シリコーン樹脂が好ましく用いられる。
【０１５８】
上記記載のシリコーン樹脂の中でも、特に三次元の網状構造を有するものが好ましく、例えば、トスパール１０３、同１０５、同１０８、同１２０、同１４５、同３１２０及び同２４０（以上東芝シリコーン（株）製）等の商品名を有する市販品が使用できる。
【０１５９】
本発明の微粒子の１次平均粒子径としては、ヘイズを低く抑えるという観点から、２０ｎｍ以下が好ましく、更に好ましくは、５〜１６ｎｍであり、特に好ましくは、５〜１２ｎｍである。
【０１６０】
本発明の微粒子の１次平均粒子径の測定は、透過型電子顕微鏡（倍率５０万〜２００万倍）で粒子を観察を行い、粒子１００個を観察し、その平均値をもって、１次平均粒子径とした。
【０１６１】
微粒子の、見掛比重としては、７０ｇ／リットル以上が好ましく、更に好ましくは、９０〜２００ｇ／リットルであり、特に好ましくは、１００〜２００ｇ／リットルである。見掛比重が大きい程、高濃度の分散液を作ることが可能になり、ヘイズ、凝集物が良化するため好ましく、また、本発明のように固形分濃度の高いドープを調製する際には、特に好ましく用いられる。
【０１６２】
１次粒子の平均径が２０ｎｍ以下、見掛比重が７０ｇ／リットル以上の二酸化珪素微粒子は、例えば、気化させた四塩化珪素と水素を混合させたものを１０００〜１２００℃にて空気中で燃焼させることで得ることができる。また例えばアエロジル２００Ｖ、アエロジルＲ９７２Ｖ（以上日本アエロジル（株）製）の商品名で市販されており、それらを使用することができる。
【０１６３】
本発明において、上記記載の見掛比重は二酸化珪素微粒子を一定量メスシリンダーに採り、この時の重さを測定し、下記式で算出した。
【０１６４】
見掛比重（ｇ／リットル）＝二酸化珪素質量（ｇ）÷二酸化珪素の容積（リットル）
本発明の微粒子の分散液を調製する方法としては、例えば以下に示すような３種類が挙げられる。
【０１６５】
《調製方法Ａ》
溶剤と微粒子を撹拌混合した後、分散機で分散を行う。これを微粒子分散液とする。微粒子分散液をドープ液に加えて撹拌する。
【０１６６】
《調製方法Ｂ》
溶剤と微粒子を撹拌混合した後、分散機で分散を行う。これを微粒子分散液とする。別に溶剤に少量のセルロースエステルを加え、撹拌溶解する。ここで添加するセルロースエステルとして、本発明の固形物を添加することが特に好ましい。
【０１６７】
これに前記微粒子分散液を加えて撹拌する。これを微粒子添加液とする。微粒子添加液をインラインミキサーでドープ液と十分混合する。
【０１６８】
《調製方法Ｃ》
溶剤に少量のセルロースエステルを加え、撹拌溶解する。これに微粒子を加えて分散機で分散を行う。これを微粒子添加液とする。微粒子添加液をインラインミキサーでドープ液と十分混合する。
【０１６９】
調製方法Ａは二酸化珪素微粒子の分散性に優れ、調製方法Ｃは二酸化珪素微粒子が再凝集しにくい点で優れている。中でも、上記記載の調製方法Ｂは二酸化珪素微粒子の分散性と、二酸化珪素微粒子がさらに再凝集しにくい等、両方に優れている好ましい調製方法である。
【０１７０】
《分散方法》
二酸化珪素微粒子を溶剤などと混合して分散するときの二酸化珪素の濃度は５〜３０質量％が好ましく、１０〜２５質量％がさらに好ましく、１５〜２０質量％が最も好ましい。分散濃度は高い方が、添加量に対する液濁度は低くなる傾向があり、ヘイズ、凝集物が良化するため好ましい。
【０１７１】
使用される溶剤は低級アルコール類としては、好ましくはメチルアルコール、エチルアルコール、プロピルアルコール、イソプロピルアルコール、ブチルアルコール等が挙げられる。低級アルコール以外の溶媒としては特に限定されないが、セルロースエステルの製膜時に用いられる溶剤を用いることが好ましい。
【０１７２】
セルロースエステルに対する二酸化珪素微粒子の添加量はセルロースエステル１００質量部に対して、二酸化珪素微粒子は０．０１〜０．３質量部が好ましく、０．０５〜０．２質量部がさらに好ましく、０．０８〜０．１２質量部が最も好ましい。添加量は多い方が、動摩擦係数に優れ、添加量が少ない方がヘイズが低く、凝集物も少ない点が優れている。
【０１７３】
分散機は通常の分散機が使用できる。分散機は大きく分けてメディア分散機とメディアレス分散機に分けられる。二酸化珪素微粒子の分散にはメディアレス分散機がヘイズが低く好ましい。
【０１７４】
メディア分散機としてはボールミル、サンドミル、ダイノミルなどがあげられる。
【０１７５】
メディアレス分散機としては超音波型、遠心型、高圧型などがあるが、本発明においては高圧分散装置が好ましい。高圧分散装置は、微粒子と溶媒を混合した組成物を、細管中に高速通過させることで、高剪断や高圧状態など特殊な条件を作りだす装置である。高圧分散装置で処理する場合、例えば、管径１〜２０００μｍの細管中で装置内部の最大圧力条件が９．８０７ＭＰａ以上であることが好ましい。更に好ましくは１９．６１３ＭＰａ以上である。またその際、最高到達速度が１００ｍ／秒以上に達するもの、伝熱速度が４２０ｋＪ／時間以上に達するものが好ましい。
【０１７６】
上記のような高圧分散装置にはＭｉｃｒｏｆｌｕｉｄｉｃｓ Ｃｏｒｐｏｒａｔｉｏｎ社製超高圧ホモジナイザ（商品名マイクロフルイダイザ）あるいはナノマイザ社製ナノマイザがあり、他にもマントンゴーリン型高圧分散装置、例えばイズミフードマシナリ製ホモジナイザ、三和機械（株）社製ＵＨＮ−０１等が挙げられる。
【０１７７】
このようにして分散された微粒子はセルロースエステルフィルム中で０．１〜１０μｍの粒径の２次粒子を含むことが好ましく、特に０．１〜５μｍの平均粒径の２次粒子であることが好ましく、特に０．２〜２μｍの平均粒径の２次粒子であることが好ましい。
【０１７８】
又、本発明のセルロースエステルフィルムには導電性を有する物質を添加することで好ましいインピーダンスを有する光学フィルムを得ることもできる。導電性物質としては特に限定はされないが、イオン導電性物質や導電性微粒子あるいはセルロースエステルと相溶性を有する帯電防止剤などを用いることができる。
【０１７９】
ここでイオン導電性物質とは電気伝導性を示し、電気を運ぶ担体であるイオンを含有する物質のことであるが、例えば、イオン性高分子化合物を挙げることができる。
【０１８０】
イオン性高分子化合物としては、特公昭４９−２３８２８号、同４９−２３８２７号、同４７−２８９３７号にみられるようなアニオン性高分子化合物；特公昭５５−７３４号、特開昭５０−５４６７２号、特公昭５９−１４７３５号、同５７−１８１７５号、同５７−１８１７６号、同５７−５６０５９号などにみられるような、主鎖中に解離基をもつアイオネン型ポリマー；特公昭５３−１３２２３号、同５７−１５３７６号、特公昭５３−４５２３１号、同５５−１４５７８３号、同５５−６５９５０号、同５５−６７７４６号、同５７−１１３４２号、同５７−１９７３５号、特公昭５８−５６８５８号、特開昭６１−２７８５３号、同６２−９３４６号にみられるような、側鎖中にカチオン性解離基をもつカチオン性ペンダント型ポリマー；等を挙げることができる。
【０１８１】
また、導電性微粒子の例としては導電性を有する金属酸化物が挙げられる。金属酸化物の例としては、ＺｎＯ、ＴｉＯ₂、ＳｎＯ₂、Ａｌ₂Ｏ₃、Ｉｎ₂Ｏ₃、ＳｉＯ₂、ＭｇＯ、ＢａＯ、ＭｏＯ₂、Ｖ₂Ｏ₅等、或いはこれらの複合酸化物が好ましく、特にＺｎＯ、ＴｉＯ₂及びＳｎＯ₂が好ましい。異種原子を含む例としては、例えばＺｎＯに対してはＡｌ、Ｉｎ等の添加、ＴｉＯ₂に対してはＮｂ、Ｔａ等の添加、又ＳｎＯ₂に対しては、Ｓｂ、Ｎｂ、ハロゲン元素等の添加が効果的である。これら異種原子の添加量は０．０１ｍｏｌ％〜２５ｍｏｌ％の範囲が好ましいが、０．１ｍｏｌ％〜１５ｍｏｌ％の範囲が特に好ましい。
【０１８２】
また、これらの導電性を有する金属酸化物粉体の体積抵抗率は１０⁷Ωｃｍ以下、特に１０⁵Ωｃｍ以下であって、１次粒子径が１０ｎｍ〜０．２μｍの粉体をフィルム内の少なくとも一部の領域に体積分率で０．０１％〜２０％含んでいることが好ましい。
【０１８３】
特に好ましくは、特開平９−２０３８１０号に記載されているアイオネン導電性ポリマーあるいは分子間架橋を有する第４級アンモニウムカチオン導電性ポリマーなどを含有することが望ましい。
【０１８４】
架橋型カチオン性導電性ポリマーの特徴は、得られる分散性粒状ポリマーにあり、粒子内のカチオン成分を高濃度、高密度に持たせることができるため、優れた導電性を有しているばかりでなく、低相対湿度下においても導電性の劣化は見られず、粒子同志も分散状態ではよく分散されているにもかかわらず、塗布後造膜過程において粒子同志の接着性もよいため膜強度も強く、また他の物質例えば支持体にも優れた接着性を有し、耐薬品性に優れている。
【０１８５】
架橋型のカチオン性導電性ポリマーである分散性粒状ポリマーは一般に約０．０１μｍ〜０．３μｍの粒子サイズ範囲にあり、好ましくは０．０５μｍ〜０．１５μｍの範囲の粒子サイズが用いられる。ここで用いている“分散性粒状性ポリマー”の語は、視覚的観察によって透明またはわずかに濁った溶液に見えるが、電子顕微鏡の下では粒状分散物として見えるポリマーである。
【０１８６】
帯電防止剤もしくはマット剤は光学フィルム全体に含まれて良いが、好ましくは光学フィルムの表層部（表面から１０μｍまでの部分）に含まれていることが好ましく、共流延等の方法によってフィルムの表面に帯電防止剤及び／又はマット剤を含有させることが好ましい。具体的には、導電性物質及び／又はマット剤を含有するドープＡと実質的にこれらを含有しないドープＢを使用し、ドープＢの少なくとも片側の面にドープＡがあるように流延されることが好ましい。（ドープＢはドープＡより少量の微粒子が含まれていても良い）
本発明のセルロースエステルフィルムは、単層のフィルムとして作製することが出来るが、共流延法等の適用により、積層フィルムとして作製することが好ましい。
【０１８７】
本発明の製造方法に適用可能な共流延の方法について説明する。
共流延とは、異なったダイを通じて２層または３層構成にする逐次多層流延方法、２つまたは３つのスリットを有するダイ内で合流させ２層または３層構成にする同時多層流延方法、逐次多層流延と同時多層流延を組み合わせた多層流延方法のいずれであっても良い。
【０１８８】
図１は、共流延法で用いられるスリットダイの断面図を示す。
流延時の膜厚は任意に設定可能であるが、Ａ面側のドープ（Ａ面側スキン層を形成）とＢ面側ドープ（Ｂ面側スキン層を形成）の乾燥後の膜厚比は１対１００〜１００対１の範囲であることが好ましい。更に好ましくは１対２０〜２０対１であり、１対１とすることもできる。一方のドープを薄く流延する場合は薄い方のウェット膜厚（ｈｗ）を０．５〜１５０μｍ、乾燥膜厚で０．１〜３０μｍとなるように流延することが好ましく、更に好ましくはウエット膜厚（ｈｗ）２．５〜１２５μｍ、乾燥膜厚で０．５〜２５μｍ、更に好ましくはウエット膜厚（ｈｗ）２５〜１００μｍ、乾燥膜厚で５〜２０μｍとなるように流延することが好ましい。
【０１８９】
尚、本発明においては、Ｂ面側のドープとは、ドープが流延用支持体に直接、接するドープを示し、Ａ面側のドープとは、支持体に接する面とは反対側の表面層を形成する及び／または流延用支持体に直接接する以外のドープを示す。
【０１９０】
３種のドープを使用する場合は、Ａ面側のドープ（Ａ面側表層を形成）とＢ面側ドープ（Ｂ面側表層を形成）、それに挟まれるフィルム内部（コア層）を形成するためのドープの乾燥後の膜厚比も任意に設定することができる。コア層とＡ面側表層もしくはＢ面側表層の乾燥後の膜厚比は１対１００〜１００対１の範囲であることが好ましく、更に好ましくは１対２０〜２０対１であり、１対１とすることもできる。フィルム内部と表層との膜厚比は１０００対１〜１対１０であることが好ましく、１００対１〜１対１がより好ましく、更に好ましくは１０対１〜２対１が好ましい。
【０１９１】
又、表層の乾燥膜厚も任意に設定できるが、０．５〜３０μｍであることが好ましく、５〜２０μｍであることが更に好ましい。又、Ａ面側表層とＢ面側表層の膜厚は同じであっても違っていても良い。例えばＡ面側表層１０μｍとし、Ｂ面側表層２０μｍとすることも可能である。
【０１９２】
２種以上のドープを用いる場合、同時に支持体上に流延してもよいし、別々に支持体上に流延してもよい。別々に流延する場合は、支持体側のドープを先に流延して支持体上である程度乾燥させた後で、その上に重ねて流延することができる。又、３種以上のドープを使用する場合、同時流延（共流延ともいう）と逐次流延を適宜組み合わせて流延し、積層構造のフィルムを作製することもできる。同時流延もしくは逐次流延によって製膜されるこれらの方法は、乾燥されたフィルム上に塗布する方法とは異なり、積層構造の各層の境界が不明確になり、断面の観察で積層構造が明確には分かれないことがあるという特徴があり、各層間の密着性を向上させる効果がある。
【０１９３】
又、本発明のセルロースエステルはフィルムにしたときの輝点異物が少ないものであることが、特に偏光板保護フィルムあるいは位相差フィルム、光学補償フィルムの支持体として好ましく用いられる。
【０１９４】
輝点異物とは、２枚の偏光板を直交に配置し（クロスニコル）、この間にセルロースエステルフィルムを配置して、一方の面から光源の光を当てて、もう一方の面からセルロースエステルフィルムを観察したときに、光源の光がもれて見える点のことである。このとき評価に用いる偏光板は輝点異物がない保護フィルムで構成されたものであることが望ましく、偏光子の保護にガラス板を使用したものが好ましく用いられる。輝点異物はセルロースエステルに含まれる未酢化のセルロースがその原因の１つと考えられ、輝点異物の少ないセルロースエステルを用いることと、セルロースエステル溶解したドープ液を濾過することによって除去し、低減することができる。又、フィルム膜厚が薄くなるほど単位面積当たりの輝点異物数は少なくなり、フィルムに含まれるセルロースエステルの含有量が少なくなるほど輝点異物は少なくなる傾向がある。
【０１９５】
輝点異物は、輝点の直径０．０１ｍｍ以上が２００個／ｃｍ²以下であることが好ましく、更に１００個／ｃｍ²以下であることが好ましく、５０個／ｃｍ²以下であることが好ましく、３０個／ｃｍ²以下であることが好ましく、１０個／ｃｍ²以下であることが好ましいが、皆無であることが最も好ましい。又、０．００５〜０．０１ｍｍ以下の輝点についても２００個／ｃｍ²以下であることが好ましく、更に１００個／ｃｍ²以下であることが好ましく、５０個／ｃｍ²以下であることが好ましく、３０個／ｃｍ²以下であることが好ましく、１０個／ｃｍ²以下であることが好ましいが、皆無であることが最も好ましい。
【０１９６】
輝点異物を濾過によって除去する場合、セルロースエステルを単独で溶解させたものを濾過するよりも可塑剤を添加混合した組成物を濾過することが輝点異物の除去効率が高く好ましい。濾材としては、ガラス繊維、セルロース繊維、濾紙、四フッ化エチレン樹脂などのフッ素樹脂等の従来公知のものが好ましく用いられるが、セラミックス、金属等も好ましく用いられる。絶対濾過精度としては５０μｍ以下のものが好ましく用いられ、３０μｍ以下のものが更に好ましく、１０μｍ以下のものが更に好ましく、５μｍ以下のものが更に好ましく用いられる。これらは適宜組み合わせて使用することもできる。濾材はサーフェースタイプでもデプスタイプでも用いることができるが、デプスタイプの方が比較的目詰まりしにくく好ましく用いられる。
【０１９７】
本発明のセルロースエステルフィルムには活性線硬化樹脂層、クリアハードコート層、防眩層、バックコート層、易接着層、配向層、液晶層、光学異方層、反射防止層、防汚層、金属酸化物層、帯電防止層、導電層を適宜組み合わせて設けることができる。これらは塗布によって設けることもできるしあるいは大気圧プラズマ処理、プラズマＣＶＤによって設けることもできる。また、偏光板保護フィルムとして特に有用である。
【０１９８】
本発明の偏光板について説明する。
本発明の偏光板は、一般的な方法で作製することができる。例えば、本発明のセルロースエステルフィルムをアルカリ処理し、沃素溶液中に浸漬延伸して作製した偏光膜の両面に、完全ケン化型ポリビニルアルコール水溶液を用いて貼り合わせる方法がある。上記記載のアルカリケン化処理とは、このときの水系接着剤の濡れを良くし、接着性を向上させるために、セルロースエステルフィルムを高温の強アルカリ液中に浸ける処理を示す。
【０１９９】
偏光板の主たる構成要素である偏光膜とは、一定方向の偏波面の光だけを通す素子であり、現在知られている代表的な偏光膜は、ポリビニルアルコール系偏光フィルムで、これはポリビニルアルコール系フィルムにヨウ素を染色させたものと二色性染料を染色させたものがある。これらは、ポリビニルアルコール水溶液を製膜し、これを一軸延伸させて染色するか、染色した後一軸延伸してから、好ましくはホウ素化合物で耐久性処理を行ったものが用いられている。該偏光膜の面上に本発明のセルロースエステルフィルムによる偏光板用保護フィルムである透明なプラスチックフィルムが張り合わされて偏光板を形成する。
【０２００】
以上のようにして得られるセルロースエステルフィルムは、特に添加した微粒子に起因すると考えられる異物故障が低減され、又、特に薄膜フィルムであっても面品質にも優れ、ブロッキング防止効果も十分で取り扱い性に優れており、光学用フィルム、特に偏光板用保護フィルムとして有用である。
【０２０１】
【実施例】
以下、実施例を挙げて本発明を具体的に説明するが、本発明はこれらに限定されない。
【０２０２】
実施例１
《固形物１〜５の調製》
表１に記載の材料をそれぞれ所定量、加圧密閉容器に投入し、８０℃に加温して容器内圧力を２気圧とし、撹拌しながらセルロースエステル及び可塑剤を完全に溶解させた。次いで、溶液を安積濾紙（株）製の安積濾紙Ｎｏ．２４４を使用して濾過した。これを金属板上に流して溶媒を蒸発させた後、支持体より引き剥がし、これを１２０℃に保持された乾燥機内で乾燥させて固形物１〜５を得た。
【０２０３】
【表１】

【０２０４】
ＣＡＰ１（セルロースアセテートプロピオネート）：アセチル置換度２．０、プロピオニル基置換度０．８、粘度平均重合度３５０
ＣＡＰ２（セルロースアセテートプロピオネート）：アセチル置換度１．６、プロピオニル基置換度１．２、粘度平均重合度４００
ＣＡＢ１（セルロースアセテートプロピオネート）：アセチル置換度１．９、ブチリル基置換度０．７、粘度平均重合度３００
ＴＡＣ１（トリアセチルセルロース）：アセチル置換度２．７
可塑剤Ａ
トリフェニルホスフェート（ＴＰＰ） ８質量部
エチルフタリルエチルグリコレート（ＥＰＥＧ） ４質量部
溶媒Ｂ
メチレンクロライド ３０６質量部
エタノール ３４質量部
溶媒Ｃ
酢酸メチル ２３８質量部
エタノール １０２質量部
（添加液１〜１０の調製）
微粒子としてアエロジルＲ９７２Ｖ（日本アエロジル（株）製）１０質量部とエタノール９０質量部をディゾルバーで３０分間撹拌混合した後、マントンゴーリンで分散を行い微粒子分散液Ｄを得た。
【０２０５】
同様に微粒子としてアエロジル２００Ｖ（日本アエロジル（株）製）１０質量部とエタノール９０質量部をディゾルバーで３０分間撹拌混合した後、マントンゴーリンで分散を行い微粒子分散液Ｅを得た。
【０２０６】
更に、表２に記載されているように前述の固形物１〜５のいずれか及び／又はセルロースエステルと紫外線吸収剤、溶媒を添加液ミキシングタンクに投入し、加熱し、撹拌しながら、完全に溶解し、更に、微粒子分散液を十分に撹拌しながらタンクに投入し、得られた混合液をフィルターで濾過をした。
【０２０７】
【表２】

【０２０８】
紫外線吸収剤Ｆ
紫外線吸収剤ＴＩＮＵＶＩＮ−３２６（チバ・スペシャルティ・ケミカルズ（株）製） ４．０質量部
紫外線吸収剤ＴＩＮＵＶＩＮ−１０９（チバ・スペシャルティ・ケミカルズ（株）製） ７．０質量部
紫外線吸収剤ＴＩＮＵＶＩＮ−１７１（チバ・スペシャルティ・ケミカルズ（株）製） ７．０質量部
溶媒Ｇ
メチレンクロライド １００質量部
溶媒Ｈ
酢酸メチル ７０質量部
エタノール １５質量部
《ドープの作製》
【０２０９】
【表３】

【０２１０】
溶媒Ｉ
メチレンクロライド ３０６質量部
エタノール ３４質量部
溶媒Ｊ
酢酸メチル ２３８質量部
エタノール １０２質量部
表３に示したように、セルロースエステル、可塑剤、溶媒を密閉容器に入れ、混合物をゆっくり攪拌しながら徐々に昇温し、６０分かけて４５℃まで上げ溶解した。容器内は１．２気圧となった。このドープを安積濾紙（株）製の安積濾紙Ｎｏ．２４４を使用して濾過した後、静置しドープ中の泡を除いた。更に添加液を添加混合し、ドープ１〜１０を得た。
【０２１１】
各ドープはスタチックミキサーにより十分混合した後、ダイからステンレスベルト上にドープ温度２５℃で流延した。ステンレスベルトの裏面から３０℃の温度の温水を接触させて温度制御されたステンレスベルト上で１分間乾燥した後、更にステンレスベルトの裏面に、１５℃の冷水を接触させて１５秒間保持した後、ステンレスベルトから剥離した。剥離時のウェブ中の残留溶媒量は１００質量％であった。次いでテンターを用いて剥離したウェブの両端をクリップで掴み、両端のクリップ間隔を巾方向に変化させることで、１２０℃で巾方向に１．０７倍に延伸した。延伸終了後、更にローラー搬送しながら１２５℃で１０分間乾燥させ表４に示すような、幅１．３ｍ、膜厚４０μｍのセルロースエステルフィルムを得た。得られたフィルムの異物故障を目視で確認した
◎：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数０個
○：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数３個未満
△：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数３〜１０個未満
×：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数１０個以上
《ロール汚れの評価方法》
２００００ｍの各々セルロースエステルフィルムを作製した後、ステンレスバンド支持体から剥離したフィルムが接する一本目のロールの汚れ具合を目視で観察し、以下のランクに分けて評価した。
【０２１２】
◎：ロールが汚れているのが全くわからない
○：ロールのごく一部がかすかに汚れている
△：ロールが全面的にかすかに汚れている
×：ロールが全面的に汚れている
◎〜△は生産が続けられるレベル
×は生産を中断してロールの清掃が必要なレベル。
【０２１３】
【表４】

【０２１４】
《セルロースエステルの置換度の測定》
ＡＳＴＭ−Ｄ８１７−９６に規定の方法に準じて行った。
【０２１５】
《セルロースエステルの数平均分子量の測定》
高速液体クロマトグラフィにより下記条件で測定する。
【０２１６】
溶媒：アセトン
カラム：ＭＰＷ×１（東ソー（株）製）
試料濃度：０．２質量／ｖ％
流量：１．０ｍｌ／分
試料注入量：３００μｌ
標準試料：ポリメタクリル酸メチル（Ｍｗ＝１８８，２００）
温度：２３℃
その結果、本発明のセルロースエステルフィルム１〜５はいずれも異物故障が少なく、さらにロール汚れも少なく、フィルム乾燥工程での微細な凹み故障も少なく、面品質に優れることが確認された。又、膜厚が薄いことによるブロッキングの発生も認められなかった。
【０２１７】
実施例２
実施例１で用いた固形物を実施例１で得られたセルロースエステルフィルムの断裁物に替えた以外は実施例１と同様にして表５のドープ液１１〜１５を調製した。
【０２１８】
【表５】

【０２１９】
各ドープはスタチックミキサーにより十分混合した後、ダイからステンレスベルト上にドープ温度２５℃で流延した。ステンレスベルトの裏面から２８℃の温度の温水を接触させて温度制御されたステンレスベルト上で１分間乾燥した後、更にステンレスベルトの裏面に、１５℃の冷水を接触させて１５秒間保持した後、ステンレスベルトから剥離した。剥離時のウェブ中の残留溶媒量は１００質量％であった。次いでテンターを用いて剥離したウェブの両端をクリップで掴み、両端のクリップ間隔を巾方向に変化させることで、１２０℃で巾方向に１．０７倍に延伸した。延伸終了後、更にローラー搬送しながら１２５℃で１０分間乾燥させ、表６に示すような幅１．３ｍ、膜厚４５μｍのセルロースエステルフィルムを得た。
【０２２０】
得られたフィルムの異物故障を目視で確認した。
◎：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数０個
○：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数３個未満
△：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数３〜１０個未満
×：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数１０個以上
【０２２１】
【表６】

【０２２２】
その結果、本発明のセルロースエステルフィルム１１〜１５はいずれも異物故障が少なく、さらにロール汚れも少なく、フィルム乾燥工程での微細な凹み故障も少なく、面品質に優れることが確認された。
【０２２３】
実施例３
実施例１及び実施例２で得られたセルロースエステルフィルム１〜１５を各々、偏光板用保護フィルムとして用い、下記の方法に従って偏光板を作製し、得られた偏光板を液晶ディスプレーに取り付け、画質の評価を行った。
【０２２４】
《偏光膜の作製》
厚さ１２０μｍのポリビニルアルコールフィルムをヨウ素１部、ヨウ化カリウム２部、ホウ酸４部を含む水溶液に浸漬し、５０℃で４倍に延伸して偏光膜を得た。
【０２２５】
《偏光板の作製》
（１）保護フィルムとして、長手方向３０ｃｍ、巾手方向１８ｃｍに切り取ったセルロースエステルフィルム試料２枚を２ｍｏｌ／リットルの水酸化ナトリウム溶液に５０℃で２分間浸漬し、さらに水洗、乾燥させた。
【０２２６】
（２）セルロースエステルフィルム試料と同サイズに調整した上記記載の偏光膜を固形分２質量％のポリビニルアルコール接着剤槽中に１〜２秒間浸漬する。
【０２２７】
（３）前記の偏光膜に付着した過剰の接着剤を軽く取り除き、前記セルロースエステルフィルム試料のＢ面上にのせ、さらにもう１枚の前記セルロースエステルフィルム試料のＢ面と接着剤とが接する様に積層し配置する。
【０２２８】
（４）ハンドローラで積層された偏光膜とセルロースエステルフィルムとの積層物の端部から過剰の接着剤及び気泡を取り除きはり合わせる。ハンドローラの圧力は約０．２〜０．３ＭＰａ、ローラスピードは２ｍ／分とした。
【０２２９】
（５）８０℃の乾燥器中に得られた試料を２分間放置し、偏光板を作製した。
次いで、得られた偏光板を下記のようにして液晶パネルに組み込み、液晶表示装置としての特性を評価した。
【０２３０】
《液晶表示装置としての特性評価》
１５型ＴＦＴ型カラー液晶ディスプレーＬＡ−１５２９ＨＭ（ＮＥＣ製）の偏光板を剥がし、上記で作製した各々の偏光板を液晶セルのサイズに合わせて断裁した。液晶セルを挟むようにして、前記作製した偏光板２枚を偏光板の偏光軸がもとと変わらないように互いに直交するように貼り付け、１５型ＴＦＴ型カラー液晶ディスプレーを作製し、セルロースエステルフィルムの偏光板としての特性を評価したところ、本発明のセルロースエステルフィルム１〜５、１１〜１５を偏光板保護フィルムとして用いた場合、異物故障、フィルムの凹み等の面品質に起因する視認性の低下がなく、液晶ディスプレーなどの画像表示装置用の偏光板として優れていることが確認された。
【０２３１】
実施例４
《固形物６の調製》
セルローストリアセテート〔アセチル置換度２．８８（Ｆｅ；０．３ｐｐｍ，Ｍｇ；１５ｐｐｍ，Ｃａ；２６ｐｐｍ）〕と可塑剤、溶媒を以下のように所定量を加圧密閉容器に投入し、８０℃に加温して容器内圧力を２気圧とし、攪拌しながら完全に溶解させた。ついで、溶液を安積濾紙（株）製の安積濾紙Ｎｏ．２６０を使用して濾過した。これを金属板上に流して溶媒を蒸発させた後、支持体より引き剥がし、これを１２０℃に保持された乾燥機内で乾燥させて固形物６を得た。
【０２３２】
セルローストリアセテート〔アセチル置換度２．８８（Ｆｅ；０．３ｐｐｍ，Ｍｇ；１５ｐｐｍ，Ｃａ；２６ｐｐｍ）〕 １００質量部
可塑剤
トリフェニルホスフェート（ＴＰＰ） ８質量部
エチルフタリルエチルグリコレート（ＥＰＥＧ） ４質量部
溶媒
メチレンクロライド ３０６質量部
エタノール ３４質量部
《添加液の調製》
微粒子としてアエロジルＲ９７２Ｖ（日本アエロジル（株）製）１０質量部とエタノール９０質量部をディゾルバーで３０分間撹拌混合した後、マントンゴーリンで分散を行い微粒子分散液を得た。
【０２３３】
更に、前述の固形物６と紫外線吸収剤、溶媒を添加液ミキシングタンクに投入し、加熱し、撹拌しながら、完全に溶解し、更に、微粒子分散液を十分に撹拌しながらタンクに投入し、得られた混合液をフィルターで濾過をして添加液を得た。
【０２３４】
紫外線吸収剤
ＴＩＮＵＶＩＮ−３２６ ４．０質量部
（チバ・スペシャルティ・ケミカルズ（株）製）
ＴＩＮＵＶＩＮ−１０９ ７．０質量部
（チバ・スペシャルティ・ケミカルズ（株）製）
ＴＩＮＵＶＩＮ−１７１ ７．０質量部
（チバ・スペシャルティ・ケミカルズ（株）製）
固形物６ ４質量部
溶媒
メチレンクロライド １００質量部
《ドープの調製》
固形物６およびセルロースエステル、可塑剤、溶媒を表７の割合で溶解釜（密閉容器）に投入してゆっくり攪拌しながら徐々に昇温し、６０分かけて４５℃まで上げ溶解し濾過した。更に添加液を混合して、ドープ１６〜２０を調製した。それぞれの添加量は表７の通りである。
【０２３５】
【表７】

【０２３６】
《フィルムの作製》
各ドープを安積濾紙（株）製の安積濾紙Ｎｏ．２６０を使用して濾過した後、ダイからステンレスベルト上にドープ温度２５℃で流延した。ステンレスベルトの裏面から３０℃の温度の温水を接触させて温度制御されたステンレスベルト上で１分間乾燥した後、更にステンレスベルトの裏面に、１０℃の冷水を接触させて１５秒間保持した後、ステンレスベルトから剥離した。剥離時のウェブ中の残留溶媒量は１００質量％であった。次いでテンターを用いて剥離したウェブの両端をクリップで掴み、両端のクリップ間隔を巾方向に変化させることで、１２０℃で残留溶媒量１０質量％で巾方向に１．０７倍に延伸した。延伸終了後、更にローラー搬送しながら１２５℃で１０分間乾燥させ表８に示すような、幅１．３ｍ、膜厚６０μｍのセルロースエステルフィルムａ〜ｅを得た。得られたフィルムの異物故障を目視で確認した。
【０２３７】
◎：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数０個
○：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数３個未満
△：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数３〜１０個未満
×：セルロースエステルフィルム長さ１００ｍあたりの直径１０μｍ以上の異物故障数１０個以上
また、ヘイズの測定及び弾性率の測定は以下のように行った。
【０２３８】
（ヘイズの測定）
ＡＳＴＭ−Ｄ１００３−５２に従って測定した。
【０２３９】
（弾性率の測定）
セルロースエステルフィルムを２３℃、５５％ＲＨで２４時間放置した後、同条件のもとで、ＪＩＳ Ｋ７１２７に従って測定した。試料はＴＤ方向（幅手方向）１０ｍｍ×ＭＤ方向（長手方向）２００ｍｍあるいはＭＤ方向１０ｍｍ×ＴＤ方向２００ｍｍに断裁し、引っ張り速度は１００ｍｍ／ｍｉｎ、標線間距離１００ｍｍで測定した。
【０２４０】
【表８】

【０２４１】
この結果、本発明のセルロースエステルフィルムｂ〜ｅは異物故障が少なく、面品質に優れたフィルムが得られることが確認された。またさらに弾性率も高い値を示す事が明らかになり、本発明のセルロースエステルフィルムは従来に比べてより高性能のフィルムであることが判明した。
【０２４２】
【発明の効果】
実施例で実証した如く、本発明によるセルロースエステル溶液の調製用固形物、セルロースエステル溶液、セルロースエステルフィルムの製造方法、セルロースエステルフィルム、それを用いた偏光板及び表示装置は微粒子あるいはセルロースエステル自身の凝集に由来する欠陥を著しく低減することを目的としており、特にセルロースエステルフィルムの面品質に優れた効果を有する。
【図面の簡単な説明】
【図１】本発明の製造方法に用いられるスリットダイの一例を示す断面図を表す。
【符号の説明】
１ 流延口
２ スリット
３ スリット[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid for preparing a cellulose ester solution (hereinafter also simply referred to as a solid), a cellulose ester solution, a method for producing a cellulose ester film (hereinafter also simply referred to as a production method), a cellulose ester film, and a polarizing plate using the same. And a display device using the same.
[0002]
[Prior art]
In recent years, development of thin and light notebook personal computers has been progressing. Along with this, the demand for thinner and higher performance protective films for polarizing plates used in display devices such as liquid crystal display devices is also increasing. In general, a triacetyl cellulose film is widely used as a protective film for a polarizing plate, but excellent scratch resistance is required for thinning.
[0003]
In order to improve the slipperiness (blocking resistance) and scratch resistance of the triacetyl cellulose film, for example, as described in JP-A Nos. 62-37113 and 61-94725, It is known to contain or apply various particles. For example, Japanese Patent Application Laid-Open No. 7-11055 proposes a fine particle having a methyl group on the surface and a method for adding the fine particle, and describes a method for preventing the fine particles from aggregating.
[0004]
However, if a large amount of fine particles are added to the film in order to increase the slipperiness, the slipperiness is improved and the scratch resistance is improved, but there is a problem that the turbidity representing the clearness of the film is deteriorated. However, it was still insufficient for use as a polarizing plate protective film that required excellent scratch resistance and sufficient clearness.
[0005]
In particular, a thin film is strongly required to improve slipperiness (blocking resistance), and therefore, it is necessary to increase the amount of fine particles added to the cellulose ester film. However, when the amount of added fine particles is increased, there is a problem that the fine particles are easily aggregated in the cellulose solution.
[0006]
In addition, the surface quality caused by the aggregation of cellulose ester itself is a factor that has a significant effect on high-definition displays. This is also one of the causes of deteriorating film surface quality.
[0007]
In this way, cellulose ester films used in various display devices are becoming increasingly demanding on flatness and surface quality, and there is a demand for improvements in defects and defects caused by fine particles and aggregates of cellulose esters themselves. It was done.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to significantly reduce defects due to aggregation of fine particles and defects due to aggregation of the cellulose ester itself in a cellulose ester film containing fine particles, and in particular, a cellulose film excellent in surface quality. It is providing the solid substance for preparation of the cellulose-ester solution for manufacturing, a cellulose-ester solution, the manufacturing method of a cellulose-ester film, a cellulose-ester film, a polarizing plate using the same, and a display apparatus.
[0009]
[Means for Solving the Problems]
The above object of the present invention has been achieved by the following constitution.
[0010]
1. A solid for preparing a cellulose ester solution containing fine particles, wherein cellulose ester and a plasticizer are dissolved and mixed in an organic solvent and then dried.
[0011]
2. A solid for preparing a cellulose ester solution containing fine particles, wherein cellulose ester and a plasticizer are dissolved and mixed in an organic solvent, the solution is filtered, and then dried to a solvent content of less than 10% by mass.
[0012]
3. A solid for preparing a cellulose ester solution containing fine particles, wherein cellulose ester and a plasticizer are dissolved in an organic solvent, the solution is filtered, and then dried to a solvent content of less than 10% by mass at 70 to 160 ° C. .
[0013]
4). 4. A solid for preparing a cellulose ester solution containing the fine particles according to any one of 1 to 3 above, wherein a cellulose ester having a total content of Ca, Mg and Fe of 100 ppm or less is used.
[0014]
5. The cellulose ester solution used in the production process of a cellulose ester film is a cellulose ester film which is casted on a support and then peeled and dried after a cellulose ester solution containing fine particles having an average particle size of less than 0.2 μm is any one of the above 1-4 A cellulose ester solution comprising the solid for preparing a cellulose ester solution according to item 1 and an organic solvent, and being prepared by adding fine particles or a fine particle dispersion.
[0015]
6). Item 5 above, wherein 10% by mass or more of the cellulose ester in the cellulose ester solution is derived from the solid material for preparing the cellulose ester solution described in any one of items 1 to 4 above. Cellulose ester solution.
[0016]
7). In addition to the cellulose ester derived from the solid for preparing a cellulose ester solution according to any one of the above 1 to 4, it contains a cellulose ester having a total content of Ca, Mg and Fe of 100 ppm or less. The cellulose ester solution as described in 6 above.
[0017]
8). The solid content concentration for preparation of the cellulose ester solution is 21 to 40% by mass, and the fine particle content is 0.009 to 0.1% by mass, according to any one of 5 to 7 above. Cellulose ester solution.
[0018]
9. 9. The cellulose ester solution as described in any one of 5 to 8 above, wherein the organic solvent contains 50% by mass or more of at least one solvent selected from methyl acetate or acetone.
[0019]
10. When the cellulose ester has an acyl group having 2 to 4 carbon atoms as a substituent, the substitution degree of the acetyl group is X, and the substitution degree of the propionyl group or butyryl group is Y, the following formulas (I) and (II The cellulose ester solution according to any one of 5 to 9 above, wherein the cellulose ester solution satisfies the above relationship.
[0020]
(I) 2.3 ≦ X + Y ≦ 3.0
(II) 0 ≦ X ≦ 2.5
11. In the manufacturing method of the cellulose-ester film which peels after drying the cellulose-ester solution containing microparticles | fine-particles with an average particle diameter of less than 0.2 micrometer on a support body, It is any one of said 5-10. A method for producing a cellulose ester film, comprising casting a cellulose ester solution.
[0021]
12 After peeling from a support body, it has the process of extending | stretching to a draw ratio x1.01-x1.5 with the amount of residual solvents of 10-100 mass%, The manufacturing of the cellulose-ester film of said 11 characterized by the above-mentioned. Method.
[0022]
13. A cellulose ester film produced by the method for producing a cellulose ester film according to 11 or 12 above.
[0023]
14 14. The cellulose ester film as described in 13 above, wherein the total content of Ca, Mg and Fe is 100 ppm or less.
[0024]
15. 15. The cellulose ester film as described in 13 or 14 above, wherein the dry film thickness of the cellulose ester film is 20 to 65 μm.
[0025]
16. 15. The cellulose ester film as described in 13 or 14 above, wherein the dry film thickness of the cellulose ester film is 20 to 45 μm.
[0026]
17. A polarizing plate comprising the cellulose ester film according to any one of 13 to 16 above.
[0027]
18. 18. A display device comprising the polarizing plate as described in 17 above.
Hereinafter, the present invention will be described in more detail.
[0028]
When preparing a cellulose ester solution containing fine particles used for solution casting, the cellulose ester film of the present invention is dissolved and mixed in advance in an organic solvent together with a plasticizer as a cellulose ester, and then a dried cellulose ester solid is added. It is characterized by that. It is desirable that the cellulose ester and the plasticizer are uniformly mixed, and it is a feature of the present invention that the solution is dried after being filtered.
[0029]
In the invention of claim 2 of the present invention, the drying is characterized in that it is dried to a residual solvent amount of less than 10% by mass, preferably less than 5% by mass, and less than 1% by mass. It is particularly preferred to be dried to
[0030]
The invention according to claim 2 of the present invention is characterized in that the drying temperature is in particular at 70 to 160 ° C., and foreign matter failure due to fine particle aggregates of the obtained cellulose film is improved.
[0031]
These solids may contain additives such as ultraviolet absorbers and fine particles.
The solid matter containing cellulose ester obtained by dissolving with a plasticizer and then drying is contained in an amount of 10 to 100% by mass of the total cellulose ester in the cellulose ester solution used for casting, and there is little aggregation of the added fine particles. Therefore, it is preferable, and it is preferable to contain especially 15-80 mass%.
[0032]
The cellulose ester solution used for casting is prepared by dissolving the solid matter in an organic solvent. If necessary, a cellulose ester, a plasticizer, and other additives are further added and dissolved. Fine particles are added to the cellulose ester solution, mixed, and cast onto a support. The fine particles can also be added in the state of a dispersion.
[0033]
In particular, when the solid content concentration of the cellulose ester solution is high, foreign matter failure of aggregates of fine particles tends to occur, but the solid content concentration is 21 to 40% by mass, and the content of fine particles is 0.009 to 0.1% by mass. By using the cellulose ester solution of the present invention, it is possible to obtain a stable quality cellulose ester film in which foreign matter failure due to aggregates of fine particles is improved.
[0034]
In particular, when the organic solvent used in the cellulose ester solution contains 50% by mass or more of methyl acetate or acetone, the cellulose ester solution has a poor stability such that the fine particles of the cellulose ester solution are easily aggregated or a gel-like insoluble matter is precipitated. However, in the cellulose ester solution containing the solid material of the present invention, it is difficult for the fine particles to aggregate, and the foreign matter failure due to the precipitation of the fine particle aggregates and gel-like insoluble matter is improved. A cellulose ester film can be obtained.
[0035]
The cellulose ester of the present invention is particularly preferably a cellulose ester having an acyl group having 2 to 4 carbon atoms as a substituent. In particular, the substitution degree of acetyl group is X, and the substitution degree of propionyl group or butyryl group is Y. In this case, a cellulose ester satisfying the relations of the formulas (I) and (II) is preferably used.
[0036]
The present invention will be described in more detail.
The acylating agent is acid chloride (CH _Three COCl, C ₂ H _Five COCl, C _Three H ₇ In the case of COCl), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804. The cellulose ester of the present invention is prepared by mixing and reacting the amount of the acylating agent according to the degree of substitution. In the cellulose ester, these acyl groups react with the hydroxyl groups of cellulose molecules.
[0037]
Cellulose molecules are composed of many glucose units linked together, and the glucose unit has three hydroxyl groups. The number of acyl groups derived from these three hydroxyl groups is called the degree of substitution (mol%). For example, cellulose triacetate has acetyl groups bonded to all three hydroxyl groups of the glucose unit (actually 2.6 to 3.0). The cellulose ester of the present invention is particularly preferably a cellulose ester having a total acyl group substitution degree of 2.8 or less because the effect of reducing foreign matter failure due to precipitation of fine particle aggregates and gel-like insolubles is particularly preferable.
[0038]
As the cellulose ester of the present invention, a cellulose ester to which a propionate group or a butyrate group is bonded in addition to an acetyl group such as cellulose acetate propionate, cellulose acetate butyrate, or cellulose acetate propionate butyrate is preferably used.
[0039]
The butyryl group that forms butyrate may be linear or branched.
[0040]
Cellulose acetate propionate containing a propionate group as a substituent has excellent water resistance and is useful as a film for liquid crystal image display devices.
[0041]
The measuring method of the substitution degree of an acyl group can be measured according to the provisions of ASTM-D817-96.
[0042]
Moreover, it is preferable that especially the dry film thickness of a cellulose-ester film is 20-45 micrometers. This is because it is desirable to increase the amount of fine particles added in order to prevent blocking in a thin cellulose ester film, and this is likely to cause failures due to aggregation of fine particles, but this is remarkably improved by the present invention. .
[0043]
Moreover, in the manufacturing method of this invention, after peeling from a support body, it extends | stretches to draw ratio x1.01- * 1.5 by residual solvent amount 2-100 mass%, More preferably, residual solvent amount 10-100 mass%. It has the process, By this, the cellulose ester film with higher surface quality can be obtained.
[0044]
The number average molecular weight of the cellulose ester of the present invention is preferably 70,000 to 250,000, which has a high mechanical strength when molded and an appropriate dope viscosity, and more preferably 80,000 to 150,000. It is.
[0045]
The cellulose used as the raw material for the cellulose ester of the present invention is not particularly limited, and examples thereof include cotton linters, wood pulp (hardwoods and conifers), and kenafs. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively. The cellulose ester according to the present invention uses an organic solvent such as acetic acid or an organic solvent such as methylene chloride when the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride). And obtained by reaction using a protic catalyst such as sulfuric acid.
[0046]
Further, the cellulose ester used in the present invention preferably has a total content of Fe, Ca and Mg of 100 ppm or less, more preferably 80 ppm or less, and further preferably 50 ppm or less. Cellulose esters having a low content of these metals are particularly preferably used because the amount of foreign matters is further reduced. These metals can be quantified using a micro digest wet decomposition apparatus (sulfuric acid decomposition), pretreatment with alkali melting, and then ICP-AES (inductively coupled plasma emission spectrometer).
[0047]
After the cellulose ester solution containing fine particles is cast on a support, the cellulose ester solution used in the production process of the cellulose ester film is peeled and dried. From the cellulose ester having a low content of Fe, Ca, and Mg. The cellulose ester derived from the prepared solid for preparing the cellulose ester solution is preferably contained in at least 10% or more of the total cellulose ester contained in the cellulose solution. More preferably, the cellulose ester component other than the cellulose ester derived from the product contains a cellulose ester having a total content of Fe, Ca, and Mg of 100 ppm or less.
[0048]
The organic solvent of the present invention is preferably capable of dissolving a cellulose ester and has an appropriate boiling point. For example, methylene chloride, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1, 4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1, 3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1 -Propanol, nitroethane and the like can be mentioned, but organic halogen compounds such as methylene chloride, dioxolane derivatives, vinegar Methyl, ethyl acetate, preferred organic solvents are acetone (i.e., good solvent), and as.
[0049]
Moreover, as shown in the following film forming process, when drying a solvent from the web (dope film | membrane) formed on the support body in a solvent evaporation process, the organic solvent used from a viewpoint which prevents foaming in a web The boiling point of the above-mentioned good solvent is, for example, methylene chloride (boiling point 40.4 ° C), methyl acetate (boiling point 56.32 ° C), acetone (56.3 ° C). , Ethyl acetate (76.82 ° C.) and the like.
[0050]
Among the good solvents described above, when methyl acetate and acetone are used, improvement of the stability of the cellulose ester solution has been a problem. According to the present invention, these solvents are particularly effective. In particular, it is preferable that 50% by mass or more of methyl acetate or acetone is contained with respect to the total organic solvent.
[0051]
In addition to the organic solvent, it is preferable to contain 0.1 to 30% by mass of an alcohol having 1 to 4 carbon atoms. It is particularly preferable that the alcohol is contained at 5 to 30% by mass.
[0052]
After casting the dope described above onto a casting support, the solvent starts to evaporate and the alcohol ratio increases and the web (dope film) gels, making the web strong and peeling from the casting support. It is also used as a gelling solvent for facilitating the dissolution, and when these ratios are small, it also has a role of promoting the dissolution of the cellulose ester of the non-chlorine organic solvent.
[0053]
Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol and the like.
[0054]
Of these, ethanol is preferred because the dope has a relatively low boiling point, relatively low boiling point, good drying properties, and no toxicity.
[0055]
A mixed solvent of methyl acetate: ethanol with a mass ratio of 95: 5 to 50:50 is preferably used, more preferably 80:20 to 60:40, and particularly preferably a solvent with a ratio of 70:30.
[0056]
Using the cellulose ester and the organic solvent described above, film formation is performed as follows.
In the present invention, the cellulose ester solution is hereinafter also referred to as cellulose ester dope or simply dope.
[0057]
The film forming process used in the method for producing a cellulose ester film of the present invention includes the following dissolving process, casting process, solvent evaporation process, peeling process, drying process and winding process. Each process will be described below.
[0058]
<< Dissolution process >>
In the cellulose ester flakes, the flakes are dissolved in an organic solvent mainly containing the above-mentioned good solvent in a kettle to form a cellulose ester solution called a dope.
[0059]
In the present invention, at least 10% by mass is prepared by previously dissolving a cellulose ester in an organic solvent together with a plasticizer, and then adding a dried solid to prepare a dope. Of the cellulose ester added to the dope, at least 10% by mass or more is preferably added as the solid, and particularly 15 to 80% by mass is preferably added as the solid.
[0060]
The solid content concentration in the dope is preferably 21.0% by mass or more. By adjusting the solid content concentration in the dope to 21.0% by mass or more, a film with less curling can be obtained, and the roll in production Although dirt can be remarkably reduced, the solid content concentration is preferably 22.0% by mass or more, and more preferably 23% by mass or more in order to further obtain the effect.
[0061]
The upper limit of the solid content concentration in the dope is not particularly limited, but if it is too high, the viscosity of the dope becomes too high, and sharkskin may occur during casting, so that the film flatness may deteriorate. It is preferable to use in.
[0062]
The dope viscosity is preferably adjusted in the range of 10 to 50 Pa · s.
When the dope concentration is increased, the added fine particles tend to aggregate over time, but the method of the present invention can improve the stability of the dope containing fine particles.
[0063]
For dissolution, a method performed at normal pressure, a method performed below the boiling point of the preferred organic solvent (that is, a good solvent) as described above, a method performed under pressure above the boiling point of the good solvent described above, and a cooling dissolution method. There are various dissolution methods such as a method of performing the method, a method of performing at a high pressure. As a method of dissolving at a temperature higher than the boiling point of the good solvent and applying a pressure that does not boil, the foaming is suppressed by pressurizing to 0.11-1.50 MPa at 40.4-120 ° C. and in a short time. Can be dissolved.
[0064]
The solvent preferably used in the present invention may be used alone or in combination, but it is preferable in terms of production efficiency to use a mixture of a good solvent and a poor solvent, and more preferably, a mixing ratio of the good solvent and the poor solvent. Is 70-95% by mass of good solvent and 30-5% by mass of poor solvent.
[0065]
The good solvent and the poor solvent preferably used in the present invention define a solvent that dissolves the cellulose ester used alone as a good solvent and a solvent that swells or does not dissolve alone. Therefore, depending on the amount of acetic acid bonded to the cellulose ester, the good solvent and the poor solvent change. For example, when acetone is used as the solvent, the amount of the acetic acid bonded to the cellulose ester is 55% and the amount of the acetic acid is 60%. Become.
[0066]
Moreover, as a poor solvent used for this invention, methanol, ethanol, n-butanol, a cyclohexane etc. are used preferably, for example.
[0067]
As the cooling dissolution method, for example, the methods described in JP-A Nos. 9-95538, 9-95544 and 9-95557 can be used. Moreover, the high-pressure dissolution method described in JP-A No. 11-21379 can also be preferably used.
[0068]
In the present invention, fine particles having an average particle size of 0.2 μm or less are added to the dissolved cellulose ester solution. The fine particles may be added as they are or as a dispersion dispersed in an organic solvent. As the organic solvent used for the dispersion, an organic solvent used for preparing the dope is preferably used. It is preferable for the stability of the dispersion that the dispersion contains a small amount of cellulose ester, and the solid material of the present invention is preferably used as the cellulose ester added to the dispersion.
[0069]
After dissolution, it is preferable to filter the dope with a filter medium, defoam it, and send it to the next step with a pump. At that time, a plasticizer, an antioxidant, a dye, an ultraviolet absorber, etc. should be added to the dope. There is.
[0070]
For example, a dope containing all of these additives can be prepared in advance and cast, but immediately before casting, the main dope mainly composed of cellulose ester and plasticizer, fine particles, and other additives ( It is also possible to appropriately mix and cast the additive liquid containing the ultraviolet absorber) etc. with an in-line mixer installed in the piping path. This method is preferable in that the amount of additive can be arbitrarily changed and adjusted, and the present invention can reduce foreign matter failures even with such a method.
[0071]
For liquid crystal display devices, it is preferable to add an antioxidant or an ultraviolet absorber that imparts durability.
[0072]
As the antioxidant, a hindered phenol compound is preferably used, and 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl). -4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3 5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3 5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl-3- ( , 5-di-t-butyl-4-hydroxyphenyl) propionate, N, N′-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5 -Trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate Etc. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination. The amount of these compounds added is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose ester.
[0073]
In addition, heat stabilizers such as kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, alumina and other inorganic fine particles, calcium, magnesium and other alkaline earth metal salts may be added. .
[0074]
Furthermore, an antistatic agent, a flame retardant, a lubricant, an oil agent and the like can be added.
《Casting process》
An endless metal belt that feeds the dope through a pressurized metering gear pump to a pressure die and infinitely transports it at the casting position or a support for casting a rotating metal drum (hereinafter sometimes simply referred to as a support) This is a step of casting a dope from a pressure die. The surface of the casting support is a mirror surface.
[0075]
Other casting methods include a doctor blade method in which the film thickness of the cast dope film is adjusted with a blade, or a reverse roll coater method in which the film is adjusted with a reverse rotating roll, but the slit shape of the die part is prepared. A pressure die that is easy to make uniform in film thickness is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.
[0076]
In order to increase the film forming speed, two or more pressure dies may be provided on the casting support, and the dope amount may be divided and stacked. In the method for producing a cellulose ester film of the present invention, it is preferable to adjust the film formation rate of the dope on the support to 30 m / min or more from the viewpoint of producing a film having a dry film thickness of 20 to 65 μm. However, from the viewpoint of obtaining a film having good flatness, it is preferable to adjust the film forming speed to 30 to 150 m / min.
[0077]
<< Solvent evaporation process >>
In the present invention, the web (in the present invention, the dope is cast on the casting support, and the formed dope film is called a web) is heated on the casting support to evaporate the solvent. In order to evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. Drying efficiency is preferred. A method of combining them is also preferable.
[0078]
<< Peeling process >>
In this step, the web in which the solvent is evaporated on the support is peeled from the support at the peeling position. The peeled web is sent to the next process.
[0079]
The web at the time of peeling When the amount of residual solvent represented by the following formula is too large, it is difficult to peel, or conversely, if it is peeled off after sufficiently drying on the support, part of the web may be peeled off Therefore, it is preferable to peel at 10 to 120%.
[0080]
The temperature at the peeling position on the support is preferably 10 to 40 ° C, more preferably 11 to 30 ° C. Further, from the viewpoint of facilitating peeling, the residual solvent amount of the web at the peeling position is preferably 20 to 100% by mass, and more preferably 40 to 90% by mass.
[0081]
The residual solvent amount of the web of the present invention is defined by the following formula.
Residual solvent amount = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100%
Note that the heat treatment in measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.
[0082]
In order to adjust the residual solvent amount at the time of peeling as described above, the surface temperature of the support for casting after casting is controlled so that the organic solvent can be efficiently evaporated from the web. It is preferable to set the temperature at the peeling position on the support to the temperature range described above. In order to control the support temperature, it is preferable to use a heat transfer method with good heat transfer efficiency. For example, a back surface heat transfer method using a liquid is preferable.
[0083]
The heat transfer method using radiant heat or hot air is difficult to control the temperature of the support and is not a preferable method. However, in a belt (support) machine, the temperature control at the place where the belt to be transferred has come down is moderate. The belt temperature can be adjusted with a gentle breeze.
[0084]
The temperature of the support can be partially changed by dividing the heating means, and can be set to different temperatures such as a casting position, a drying part, and a peeling position of the casting support.
[0085]
As a method for increasing the film forming speed (the film forming speed can be increased because the film is peeled off while the residual solvent amount is as large as possible), there is a gel casting method (gel casting) in which even a large amount of residual solvent can be removed.
[0086]
For example, a poor solvent for the cellulose ester is added to the dope, and after the dope is cast, the gel is formed, and the temperature of the support is lowered to form a gel.
[0087]
There is also a method of adding a metal salt in the dope.
By gelling on the support and strengthening the film, it is possible to speed up the peeling and increase the film forming speed.
[0088]
When peeling at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be damaged, or slippage and vertical stripes due to peeling tension will tend to occur, and the amount of residual solvent will be reduced in consideration of economic speed and quality. It is decided.
[0089]
The release tension is usually 196 to 245 N / m when the support and the film are peeled, but the content of the UV absorber per unit mass of the cellulose ester is large, and the film is made thinner than before. In the cellulose ester film of the present invention, since wrinkles are likely to occur at the time of peeling, it is preferable to peel at a minimum tension of 166.6 N / m, more preferably at a minimum tension of 137.2 N / m. It is to peel. More preferably, the minimum tension is peeled at 100 N / m. In-plane retardation R the lower the peel tension ₀ Is preferable because it can be kept low.
[0090]
In-plane retardation R as a polarizing plate protective film ₀ Is preferably less than 20 nm, more preferably less than 10 nm, and even more preferably less than 5 nm. Most preferably, it is 0-1 nm.
[0091]
On the other hand, when the cellulose ester film of the present invention is used as a retardation film, R is obtained by stretching the film after peeling. ₀ May be 20 to 1000 nm. Thereby, for example, a 1 / 4λ plate, a 1 / 2λ plate, and the like can be manufactured.
[0092]
In-plane retardation is measured with a three-dimensional refractive index at a wavelength of 590 nm using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments). From the obtained refractive indexes nx, ny and nz Can be calculated. Moreover, the retardation value R in the film thickness direction _t Can be made from 0 to 400 nm. Preferably, the thing of 30-250 nm is obtained preferably.
[0093]
The cellulose ester film of the present invention has an in-plane retardation R and an angle θ formed by the slow axis direction and the film forming direction. ₀ Is preferably used as a support for a polarizing plate protective film or an optical compensation film.
[0094]
P ≦ 1-sin ² (2θ) × sin ² (ΠR ₀ / Λ)
P is 0.9999, λ is R ₀ And the wavelength of light 590 nm in the three-dimensional refractive index measurement for obtaining θ (radian).
[0095]
<< Drying process >>
It is a step of drying the web while holding the width by using a drying device that alternately conveys the web through rolls arranged in a staggered pattern and / or a tenter device that conveys while holding both ends of the web with clips and pins. .
[0096]
It is R to maintain the transport tension in the drying process as low as possible. ₀ Is preferably low, and is preferably 190 N / m or less. More preferably, it is 170 N / m or less, More preferably, it is 140 N / m or less, It is especially preferable that it is 100-130 N / m. In particular, it is effective to maintain it below the transport tension until the amount of residual solvent in the film is at least 5% by mass or less.
[0097]
As a drying means, hot air is generally blown on both sides of the web, but there is also a means of heating by applying microwaves instead of wind. Too much drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent.
[0098]
Throughout the whole, the drying temperature is usually 40 to 250 ° C, more preferably 70 to 180 ° C.
[0099]
The drying temperature, the amount of drying air, and the drying time differ depending on the solvent used, and the drying conditions may be appropriately selected according to the type and combination of the solvents used.
[0100]
In the drying step after peeling from the casting support surface, the web tends to shrink in the width direction due to evaporation of the solvent. Shrinkage increases as the temperature rapidly dries.
[0101]
Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the finished film.
[0102]
From this point of view, for example, a method of drying the entire drying process or a part of the process as shown in JP-A-62-46625 while holding the width ends of the web with a clip in the width direction (tenter method and Is preferred).
[0103]
In addition, it turned out that the effect that the curl of the film obtained by drying while gripping width in this way can be made small is acquired. At this time, the draw ratio in the width direction is preferably x1.01 to x1.50, more preferably x1.01 to x1.20, and x1.03 to x1.10. More preferably it is.
[0104]
When performing the tenter, the residual solvent amount of the web is preferably 35% by mass or less at the start of the tenter, and it is preferable to perform drying while applying the tenter until the residual solvent amount of the web becomes 10% by mass or less. More preferably, it is 5% by mass or less.
[0105]
Moreover, in the drying process of the cellulose ester film, the film peeled off from the support is further dried, and the residual solvent amount is preferably 3% by mass or less, more preferably 0.5% by mass or less.
[0106]
In the film drying process, generally, a method of drying while conveying a film by a roll suspension method, a pin tenter method or a clip tenter method is adopted. For the liquid crystal display member, it is preferable to dry while maintaining the width by a pin tenter method in order to improve the dimensional stability. In particular, it is particularly preferable to maintain the width in a large amount of residual solvent immediately after peeling from the support because the effect of improving dimensional stability is more exhibited.
[0107]
The means for drying the film is not particularly limited, and is generally performed with hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to carry out with hot air in terms of simplicity. The drying temperature is preferably divided into 3 to 5 stages in the range of 40 to 150 ° C and gradually increased, and more preferably in the range of 80 to 140 ° C in order to improve dimensional stability.
[0108]
Here, it is preferable that the film dried to a residual solvent amount of less than 10% by mass is returned to the dissolving step and used for preparing the cellulose ester solution.
[0109]
<Winding process>
This is a step of winding up as a cellulose ester film after the residual solvent amount in the web is 2% by mass or less, and a film having good dimensional stability can be obtained by making the residual solvent amount 0.4% by mass or less. I can do it.
[0110]
As a winding method, a generally used method may be used. There are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.
[0111]
The film thickness of the cellulose ester film varies depending on the purpose of use, but the finished film is usually in the range of 5 to 500 μm, more preferably in the range of 20 to 250 μm, particularly in the range of 20 to 120 μm as the film for a liquid crystal image display device. Is preferred. In particular, in 20 to 65 μm, defects due to aggregation of the cellulose ester itself can be reduced. Further, in the cellulose ester film having a thickness of 20 to 45 μm, it is necessary to increase the amount of added fine particles in order to prevent blocking. Failures often become a problem, but the present invention can greatly reduce foreign matter failures.
[0112]
To adjust the film thickness, it is necessary to control the dope concentration, the pumping amount of the pump, the slit gap of the die base, the extrusion pressure of the die, the speed of the casting support, etc. so as to obtain the desired thickness. Good.
[0113]
Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices. In the process from immediately after casting through the solution casting film forming method to drying, the atmosphere in the drying apparatus may be air, or may be performed in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas.
[0114]
Of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be taken into account.
[0115]
The cellulose ester film of the present invention preferably contains a plasticizer.
As the plasticizer, phosphoric acid esters and carboxylic acid esters are preferably used. In the present invention, it is particularly preferable to include a plasticizer having a melting point of 25 ° C. or lower, and the cellulose ester film has a melting point of less than 25 ° C. More preferably, a plasticizer of 25 ° C. or higher is used in combination.
[0116]
The plasticizer is not particularly limited. Examples of the phosphate ester plasticizer include triphenyl phosphate (TPP) and tricresyl phosphate (TCP), biphenyl-diphenyl phosphate, dimethyl ethyl phosphate, cresyl diphenyl phosphate, octyl diphenyl. Examples include phosphate, diphenylbiphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like.
[0117]
Representative examples of the carboxylic acid ester plasticizer include phthalic acid esters and citric acid esters. Examples of the phthalic acid ester include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diethyl hexyl phthalate (DEHP), ethyl phthalyl ethyl glycolate and the like.
[0118]
As the citrate plasticizer, acetyl triethyl citrate (OACTE), acetyl tributyl citrate (OACTB), or the like is used.
[0119]
As glycolic acid ester plasticizers, triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate (EPEG), methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. may be used alone or in combination. Is preferred.
[0120]
Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters.
[0121]
In the present invention, it is particularly preferable to use a phosphate ester plasticizer in combination with a plasticizer having a melting point of less than 25 ° C. because of excellent dimensional stability and water resistance.
[0122]
The plasticizer having a melting point of less than 25 ° C. is not particularly limited as long as the melting point is less than 25 ° C., and can be selected from the above plasticizers. Examples thereof include tricresyl phosphate, cresyl diphenyl phosphate, tributyl phosphate, diethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, triacetin, ethyl phthalyl ethyl glycolate and the like. These plasticizers are preferably used alone or in combination.
[0123]
The plasticizer having a melting point of less than 25 ° C used in the present invention preferably has a melting point of 5 to 25 ° C.
[0124]
Examples of the plasticizer having a melting point of 25 ° C. or higher include diethoxyethyl phthalate (melting point 34 ° C.), triphenyl phosphate (melting point 48.5 ° C.), benzophenone (melting point 48 ° C.), camphor (melting point 152 ° C.), o- Examples include cresyl-p-toluenesulfonate (52.5 ° C.), cyclohexyl-p-toluenesulfonamide (86 ° C.), methyl benzoyl benzoate (52 ° C.), ethyl benzoyl benzoate (melting point 58 ° C.) and the like.
[0125]
The melting point in the present invention is the melting point of the true freezing point described in the Chemical Dictionary of Kyoritsu Publishing Co., Ltd. In addition, a polymer plasticizer having a molecular weight of about 1000 to 100,000, such as polyester or acrylic resin or polyvinyl acetate copolymer, is also preferably used.
[0126]
The amount of these plasticizers used is preferably 1 to 15% by mass with respect to the cellulose ester in terms of film performance and processability. For a liquid crystal display member, 5 to 15% by mass is more preferable from the viewpoint of dimensional stability, and 7 to 12% by mass is particularly preferable. In the present invention, the total content of the plasticizer having a melting point of 25 ° C. or more and the plasticizer having a melting point of less than 25 ° C. in the cellulose ester film is preferably 1 to 20% by mass.
[0127]
Moreover, 1-10 mass% is preferable, and, as for content of the plasticizer whose melting | fusing point is less than 25 degreeC with respect to a cellulose-ester film, More preferably, it is 3-7 mass%.
[0128]
A larger proportion of the plasticizer having a melting point of less than 25 ° C. among all the plasticizers is preferable because the flexibility of the cellulose ester film is improved and the processability is excellent.
[0129]
It is preferable to use a plasticizer having a melting point of less than 25 ° C. in an amount of 1% by mass or more based on the cellulose ester because the flexibility of the cellulose ester film is improved and the processability is excellent. When a plasticizer having a temperature of less than 14 ° C. is used, the processability is better and preferable.
[0130]
Processability is when slitting or punching a base film or a liquid crystal display member. If the processability is poor, the cut surface will be saw-toothed and chips will be generated, which will be attached to the product and cause defects. Absent.
[0131]
The plasticizer content contained in the solid material of the present invention is preferably 3 to 30% by mass, and the plasticizer is appropriately used.
[0132]
The ultraviolet absorber preferably used for the cellulose ester film of the present invention will be described.
[0133]
The cellulose ester film of the present invention is used for a polarizing plate or a liquid crystal display member because of its high dimensional stability, but an ultraviolet absorber is preferably used from the viewpoint of preventing deterioration of the polarizing plate or the liquid crystal.
[0134]
As the ultraviolet absorber, those excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and having little absorption of visible light having a wavelength of 400 nm or more are preferably used from the viewpoint of good liquid crystal display properties. Specifically, the transmittance at 380 nm is preferably less than 10%, more preferably less than 5%.
[0135]
Specific examples of the ultraviolet absorber preferably used in the present invention include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Further, a polymeric ultraviolet absorber described in JP-A-6-148430 is also preferably used.
[0136]
As the benzotriazole ultraviolet absorber, a compound represented by the following general formula [1] is preferably used.
[0137]
[Chemical 1]

[0138]
Where R ₁ , R ₂ , R _Three , R _Four And R _Five May be the same or different, and may be a hydrogen atom, halogen atom, nitro group, hydroxyl group, alkyl group, alkenyl group, aryl group, alkoxyl group, acyloxy group, aryloxy group, alkylthio group, arylthio group, mono- or dialkylamino group Represents an acylamino group or a 5- to 6-membered heterocyclic group, R _Four And R _Five May be closed to form a 5-6 membered carbocyclic ring.
[0139]
Moreover, these groups described above may have an arbitrary substituent.
Although the specific example of the ultraviolet absorber preferably used for this invention below is given, this invention is not limited to these.
[0140]
UV-1: 2- (2'-hydroxy-5'-methylphenyl) benzotriazole
UV-2: 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) benzotriazole
UV-3: 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole
UV-4: 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole
UV-5: 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole
UV-6: 2,2-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol)
UV-7: 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole
UV-8: 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol (TINUVIN171, manufactured by Ciba)
UV-9: Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl- 4-Hydroxy-5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate (TINUVIN109, manufactured by Ciba)
Moreover, as a benzophenone type ultraviolet absorber which is one of the ultraviolet absorbers preferably used in the present invention, a compound represented by the following general formula [2] is preferably used.
[0141]
[Chemical 2]

[0142]
In the formula, Y represents a hydrogen atom, a halogen atom or an alkyl group, an alkenyl group, an alkoxyl group, and a phenyl group, and these alkyl group, alkenyl group, and phenyl group may have a substituent. A is a hydrogen atom, an alkyl group, an alkenyl group, a phenyl group, a cycloalkyl group, an alkylcarbonyl group, an alkylsulfonyl group, or —CO (NH). _n-1 -D group is represented, D represents the alkyl group, the alkenyl group, or the phenyl group which may have a substituent. m and n represent 1 or 2.
[0143]
In the above, the alkyl group represents, for example, a linear or branched aliphatic group having up to 24 carbon atoms, the alkoxy group includes, for example, an alkoxy group up to 18 carbon atoms, and the alkenyl group includes, for example, 16 carbon atoms. An alkenyl group up to, for example, an allyl group, a 2-butenyl group, or the like. In addition, as substituents for alkyl groups, alkenyl groups and phenyl groups, halogen atoms such as chlorine atoms, bromine atoms and fluorine atoms, hydroxyl groups and phenyl groups (this phenyl group is substituted with alkyl groups or halogen atoms, etc.) May be used).
[0144]
Specific examples of the benzophenone compound represented by the general formula [2] are shown below, but the present invention is not limited thereto.
[0145]
UV-10: 2,4-dihydroxybenzophenone
UV-11: 2,2'-dihydroxy-4-methoxybenzophenone
UV-12: 2-hydroxy-4-methoxy-5-sulfobenzophenone
UV-13: Bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane)
The ultraviolet absorber described above preferably used in the present invention is preferably a benzotriazole-based ultraviolet absorber or a benzophenone-based ultraviolet absorber, which has high transparency and is excellent in the effect of preventing the deterioration of the polarizing plate and the liquid crystal element, and unnecessary coloring. A benzotriazole-based ultraviolet absorber with a lower content is particularly preferably used.
[0146]
Examples of the method for adding the ultraviolet absorber addition liquid include the methods described below.
<< Addition method A >>
As a method for preparing the ultraviolet absorber addition liquid, the ultraviolet absorber is dissolved in an organic solvent such as alcohol, methylene chloride, dioxolane, etc. and then added directly into the dope composition.
[0147]
<< Addition method B >>
As a method for preparing the ultraviolet absorber addition liquid, an ultraviolet absorber and a small amount of cellulose ester and / or a solid substance of the present invention are dissolved in an organic solvent such as alcohol, methylene chloride, dioxolane, and then added to the dope with an in-line mixer. .
[0148]
In the present invention, the addition method B is preferable because the addition amount of the ultraviolet absorber can be easily adjusted, so that the productivity is excellent.
[0149]
The amount of UV absorber used is not uniform depending on the type of compound and conditions of use, but usually 1m of cellulose ester film. ² It is preferably 0.2 to 5.0 g, more preferably 0.4 to 2.0 g, and particularly preferably 0.6 to 1.0 g.
[0150]
In the present invention, in particular, an ultraviolet absorber having a melting point of 20 ° C. or lower is preferably used.
[0151]
In general, many ultraviolet absorbers have poor solubility, but it has been found that the presence of a plasticizer that is liquid at 25 ° C. facilitates dissolution. Therefore, in the case of a structure containing a plasticizer that is liquid at 25 ° C., it is possible to sufficiently add an ultraviolet absorber and dissolve it with a margin, which is particularly effective when preparing a high concentration dope. In particular, it has become possible to provide a film having a film thickness of 45 μm or less and sufficient ultraviolet absorbing ability. Furthermore, by containing an ultraviolet absorber that is liquid at 20 ° C. and a plasticizer that is liquid at 25 ° C., a higher concentration of ultraviolet absorber and plasticizer can be contained, and the film has excellent transparency. It was possible to impart wettability and ultraviolet absorbing ability, and the effect of reducing process contamination due to precipitation of these additives was also obtained.
[0152]
In addition, polymeric ultraviolet absorbers described in JP-A-6-148430 and Japanese Patent Application No. 12-156039 can also be preferably used.
[0153]
The fine particles of the present invention will be described.
The fine particles of the present invention include inorganic compound fine particles or organic compound fine particles.
[0154]
Inorganic compounds include silicon-containing compounds, silicon dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, etc. More preferably, it is an inorganic compound containing silicon or zirconium oxide, but silicon dioxide is particularly preferably used because the turbidity of the cellulose ester film can be reduced.
[0155]
As the fine particles of silicon dioxide, for example, commercially available products such as Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (above Nippon Aerosil Co., Ltd.) can be used.
[0156]
As the fine particles of zirconium oxide, for example, commercially available products such as Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) can be used.
[0157]
As the organic compound, for example, a polymer such as a silicone resin, a fluorine resin, and an acrylic resin is preferable, and among these, a silicone resin is preferably used.
[0158]
Among the above-described silicone resins, those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120 and 240 (above Toshiba Silicone Co., Ltd.) ) Etc. can be used.
[0159]
The primary average particle diameter of the fine particles of the present invention is preferably 20 nm or less, more preferably 5 to 16 nm, and particularly preferably 5 to 12 nm from the viewpoint of suppressing haze.
[0160]
The primary average particle diameter of the fine particles of the present invention is measured by observing particles with a transmission electron microscope (magnification of 500,000 to 2,000,000 times), observing 100 particles, and using the average value, the primary average particle size is measured. The diameter.
[0161]
The apparent specific gravity of the fine particles is preferably 70 g / liter or more, more preferably 90 to 200 g / liter, and particularly preferably 100 to 200 g / liter. A larger apparent specific gravity makes it possible to make a high-concentration dispersion, which improves haze and agglomerates, and is preferable when preparing a dope having a high solid content concentration as in the present invention. Are particularly preferably used.
[0162]
Silicon dioxide fine particles having an average primary particle diameter of 20 nm or less and an apparent specific gravity of 70 g / liter or more are, for example, a mixture of vaporized silicon tetrachloride and hydrogen burned in air at 1000 to 1200 ° C. Can be obtained. For example, it is marketed with the brand name of Aerosil 200V and Aerosil R972V (above Nippon Aerosil Co., Ltd. product), and can use them.
[0163]
In the present invention, the apparent specific gravity described above was calculated by the following equation by measuring a weight of silicon dioxide fine particles in a graduated cylinder and measuring the weight at that time.
[0164]
Apparent specific gravity (g / liter) = Mass of silicon dioxide (g) ÷ Volume of silicon dioxide (liter)
Examples of the method for preparing the dispersion of fine particles of the present invention include the following three types.
[0165]
<< Preparation Method A >>
After stirring and mixing the solvent and the fine particles, dispersion is performed with a disperser. This is a fine particle dispersion. The fine particle dispersion is added to the dope solution and stirred.
[0166]
<< Preparation Method B >>
After stirring and mixing the solvent and the fine particles, dispersion is performed with a disperser. This is a fine particle dispersion. Separately, a small amount of cellulose ester is added to the solvent and dissolved by stirring. As the cellulose ester added here, it is particularly preferable to add the solid material of the present invention.
[0167]
The fine particle dispersion is added to this and stirred. This is a fine particle addition solution. The fine particle additive solution is sufficiently mixed with the dope solution using an in-line mixer.
[0168]
<< Preparation Method C >>
Add a small amount of cellulose ester to the solvent and dissolve with stirring. Fine particles are added to this and dispersed by a disperser. This is a fine particle addition solution. The fine particle additive solution is sufficiently mixed with the dope solution using an in-line mixer.
[0169]
Preparation method A is excellent in dispersibility of silicon dioxide fine particles, and preparation method C is excellent in that silicon dioxide fine particles are difficult to re-aggregate. Among them, the preparation method B described above is a preferable preparation method that is excellent in both dispersibility of the silicon dioxide fine particles and that the silicon dioxide fine particles are less likely to reaggregate.
[0170]
《Distribution method》
The concentration of silicon dioxide when the silicon dioxide fine particles are mixed and dispersed with a solvent is preferably 5 to 30% by mass, more preferably 10 to 25% by mass, and most preferably 15 to 20% by mass. A higher dispersion concentration is preferable because liquid turbidity with respect to the added amount tends to be low, and haze and aggregates are improved.
[0171]
The solvent used is preferably lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like. Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film forming of a cellulose ester.
[0172]
The amount of silicon dioxide fine particles added to cellulose ester is preferably 0.01 to 0.3 parts by mass, more preferably 0.05 to 0.2 parts by mass, and more preferably 0.05 to 0.2 parts by mass with respect to 100 parts by mass of cellulose ester. Most preferred is 08 to 0.12 parts by mass. The larger the added amount, the better the dynamic friction coefficient, and the smaller the added amount, the lower the haze and the fewer agglomerates.
[0173]
As the disperser, a normal disperser can be used. Dispersers can be broadly divided into media dispersers and medialess dispersers. For dispersing silicon dioxide fine particles, a medialess disperser is preferred because of its low haze.
[0174]
Examples of the media disperser include a ball mill, a sand mill, and a dyno mill.
[0175]
Examples of the medialess disperser include an ultrasonic type, a centrifugal type, and a high pressure type. In the present invention, a high pressure disperser is preferable. The high pressure dispersion device is a device that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube. When processing with a high-pressure dispersion apparatus, for example, the maximum pressure condition inside the apparatus is preferably 9.807 MPa or more in a thin tube having a tube diameter of 1 to 2000 μm. More preferably, it is 19.613 MPa or more. Further, at that time, those having a maximum reaching speed of 100 m / second or more and those having a heat transfer speed of 420 kJ / hour or more are preferable.
[0176]
The high-pressure dispersion apparatus as described above includes an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and other manton gorin type high-pressure dispersion apparatuses such as a homogenizer manufactured by Izumi Food Machinery, Examples include UHN-01 manufactured by Wako Machine Co., Ltd.
[0177]
The fine particles dispersed in this manner preferably contain secondary particles having a particle size of 0.1 to 10 μm in the cellulose ester film, and in particular, secondary particles having an average particle size of 0.1 to 5 μm. In particular, secondary particles having an average particle diameter of 0.2 to 2 μm are preferable.
[0178]
Moreover, the optical film which has preferable impedance can also be obtained by adding the substance which has electroconductivity to the cellulose-ester film of this invention. Although it does not specifically limit as an electroconductive substance, The antistatic agent etc. which have compatibility with an ionic electroconductive substance, electroconductive fine particles, or a cellulose ester can be used.
[0179]
Here, the ion conductive substance is a substance that shows electric conductivity and contains ions that are carriers for carrying electricity, and examples thereof include ionic polymer compounds.
[0180]
Examples of the ionic polymer compound include anionic polymer compounds such as those described in JP-B-49-23828, JP-A-49-23827, and JP-A-47-28937; JP-B-55-734, JP-A-50-54672 Ionene type polymers having a dissociating group in the main chain, as seen in JP-B Nos. 59-14735, 57-18175, 57-18176, 57-56059, etc .; No. 57-15376, No. 53-45231, No. 55-145783, No. 55-65950, No. 55-67746, No. 57-11342, No. 57-19735, No. 58-56858. No., JP-A 61-27853, 62-9346, and a cationic pendant type having a cationic dissociation group in the side chain Rimmer; and the like.
[0181]
Examples of conductive fine particles include conductive metal oxides. Examples of metal oxides include ZnO, TiO ₂ , SnO ₂ , Al ₂ O _Three , In ₂ O _Three , SiO ₂ , MgO, BaO, MoO ₂ , V ₂ O _Five Or composite oxides thereof are preferable, in particular ZnO, TiO. ₂ And SnO ₂ Is preferred. Examples of containing different atoms include, for example, addition of Al, In, etc. to ZnO, TiO ₂ For Nb, Ta, etc., and SnO ₂ In contrast, the addition of Sb, Nb, halogen elements and the like is effective. The amount of these different atoms added is preferably in the range of 0.01 mol% to 25 mol%, but is particularly preferably in the range of 0.1 mol% to 15 mol%.
[0182]
The volume resistivity of these conductive metal oxide powders is 10 ⁷ Ωcm or less, especially 10 ^Five It is preferable that a powder having a primary particle diameter of 10 nm to 0.2 μm is contained in an area of 0.01% to 20% in a volume fraction in at least a part of the film.
[0183]
It is particularly preferable to contain an ionene conductive polymer described in JP-A-9-203810 or a quaternary ammonium cation conductive polymer having intermolecular crosslinking.
[0184]
The characteristic of the cross-linked cationic conductive polymer is the dispersible granular polymer obtained, and since it can have a high concentration and high density of the cationic component in the particles, it only has excellent conductivity. No deterioration of conductivity was observed even under low relative humidity, and although the particles were well dispersed in the dispersed state, the adhesion of the particles was good in the film-forming process after coating, so the film strength was also low. It is strong and has excellent adhesion to other substances such as supports, and has excellent chemical resistance.
[0185]
The dispersible granular polymer, which is a crosslinked cationic conductive polymer, generally has a particle size range of about 0.01 μm to 0.3 μm, preferably a particle size of 0.05 μm to 0.15 μm. As used herein, the term “dispersible particulate polymer” is a polymer that appears to be a clear or slightly turbid solution by visual observation but appears as a granular dispersion under an electron microscope.
[0186]
The antistatic agent or matting agent may be contained in the entire optical film, but it is preferably contained in the surface layer portion (the portion from the surface to 10 μm) of the optical film. It is preferable to contain an antistatic agent and / or a matting agent on the surface. Specifically, a dope A containing a conductive material and / or a matting agent and a dope B substantially not containing these are used, and the dope B is cast so that the dope A is present on at least one side of the dope B. It is preferable. (Dope B may contain a smaller amount of fine particles than Dope A)
The cellulose ester film of the present invention can be produced as a single layer film, but is preferably produced as a laminated film by application of a co-casting method or the like.
[0187]
A co-casting method applicable to the production method of the present invention will be described.
Co-casting is a sequential multilayer casting method in which two or three layers are configured through different dies, and a simultaneous multilayer casting method in which two or three slits are combined in a die having two or three slits. Any of the multilayer casting methods combining sequential multilayer casting and simultaneous multilayer casting may be used.
[0188]
FIG. 1 shows a cross-sectional view of a slit die used in the co-casting method.
The film thickness at the time of casting can be arbitrarily set, but the film thickness ratio after drying of the dope on the A side (forms the A side skin layer) and the B side dope (forms the B side skin layer) is A range of 1 to 100 to 100 to 1 is preferable. More preferably, it is 1: 20-20: 1, and can be 1: 1. When one dope is cast thinly, it is preferably cast so that the thinner wet film thickness (hw) is 0.5 to 150 μm and the dry film thickness is 0.1 to 30 μm, more preferably wet. The film thickness (hw) is 2.5 to 125 μm, the dry film thickness is 0.5 to 25 μm, more preferably the wet film thickness (hw) is 25 to 100 μm, and the dry film thickness is 5 to 20 μm. preferable.
[0189]
In the present invention, the B-side dope refers to a dope in which the dope is in direct contact with the casting support, and the A-side dope is a surface layer opposite to the surface in contact with the support. And / or dopes other than in direct contact with the casting support.
[0190]
When three types of dopes are used, in order to form an A-side dope (forms the A-side surface layer), a B-side dope (forms the B-side surface layer), and the film interior (core layer) sandwiched between them The film thickness ratio after drying of the dope can also be set arbitrarily. The thickness ratio after drying of the core layer and the A-side surface layer or B-side surface layer is preferably in the range of 1 to 100 to 100 to 1, more preferably 1 to 20 to 20 to 1. It can also be 1. The film thickness ratio between the inside of the film and the surface layer is preferably 1000: 1 to 1:10, more preferably 100: 1 to 1: 1, and still more preferably 10: 1 to 2: 1.
[0191]
Moreover, although the dry film thickness of a surface layer can also be set arbitrarily, it is preferable that it is 0.5-30 micrometers, and it is still more preferable that it is 5-20 micrometers. The film thicknesses of the A-side surface layer and the B-side surface layer may be the same or different. For example, the A-side surface layer may be 10 μm and the B-side surface layer may be 20 μm.
[0192]
When using 2 or more types of dope, you may cast on a support body simultaneously, and you may cast on a support body separately. In the case of casting separately, the dope on the support side can be cast first and dried to some extent on the support, and then overlaid on the support. When three or more kinds of dopes are used, a film having a laminated structure can be produced by appropriately combining simultaneous casting (also referred to as co-casting) and sequential casting. Unlike the method of coating on a dried film, these methods, which are formed by simultaneous casting or sequential casting, make the boundary of each layer of the laminated structure unclear, and the laminated structure is clear by observing the cross section. There is a feature that there is a case where there is no separation, there is an effect of improving the adhesion between each layer.
[0193]
Further, the cellulose ester of the present invention is preferably used as a support for a polarizing plate protective film, a retardation film, or an optical compensation film, in particular, having a small amount of bright spot foreign matters when formed into a film.
[0194]
A bright spot foreign material is an arrangement in which two polarizing plates are arranged orthogonally (crossed Nicols), a cellulose ester film is arranged between them, light from the light source is applied from one side, and the cellulose ester film is applied from the other side. This is the point where the light from the light source appears to be leaked. At this time, the polarizing plate used for the evaluation is desirably composed of a protective film having no bright spot foreign matter, and a polarizing plate using a glass plate for protecting the polarizer is preferably used. The bright spot foreign matter is considered to be one of the causes due to the unacetylated cellulose contained in the cellulose ester, and is reduced by using the cellulose ester with less bright spot foreign matter and filtering the dope solution in which the cellulose ester is dissolved. can do. Further, the thinner the film thickness, the smaller the number of bright spot foreign matter per unit area, and the lower the content of cellulose ester contained in the film, the fewer bright spot foreign matter.
[0195]
The bright spot foreign matter has a bright spot diameter of 0.01 mm or more of 200 pieces / cm. ² Or less, more preferably 100 / cm ² Or less, preferably 50 / cm ² Or less, preferably 30 / cm ² Preferably, the number is 10 / cm ² The following is preferred, but most preferably none. Also, for bright spots of 0.005 to 0.01 mm or less, 200 / cm ² Or less, more preferably 100 / cm ² Or less, preferably 50 / cm ² Or less, preferably 30 / cm ² Preferably, the number is 10 / cm ² The following is preferred, but most preferably none.
[0196]
When removing bright spot foreign matter by filtration, it is preferable to filter the composition in which a plasticizer is added and mixed, rather than filtering a cellulose ester dissolved alone, because the bright spot foreign matter removal efficiency is high. As the filter medium, conventionally known materials such as glass fibers, cellulose fibers, filter paper, and fluororesins such as tetrafluoroethylene resin are preferably used, but ceramics, metals and the like are also preferably used. The absolute filtration accuracy is preferably 50 μm or less, more preferably 30 μm or less, still more preferably 10 μm or less, and even more preferably 5 μm or less. These can be used in combination as appropriate. The filter medium can be either a surface type or a depth type, but the depth type is preferably used because it is relatively less clogged.
[0197]
The cellulose ester film of the present invention has an actinic ray curable resin layer, a clear hard coat layer, an antiglare layer, a back coat layer, an easy adhesion layer, an alignment layer, a liquid crystal layer, an optical anisotropic layer, an antireflection layer, an antifouling layer, A metal oxide layer, an antistatic layer, and a conductive layer can be provided in appropriate combination. These can be provided by coating, or can be provided by atmospheric pressure plasma treatment or plasma CVD. Moreover, it is particularly useful as a polarizing plate protective film.
[0198]
The polarizing plate of the present invention will be described.
The polarizing plate of the present invention can be produced by a general method. For example, there is a method in which a cellulose ester film of the present invention is alkali-treated and bonded to both surfaces of a polarizing film produced by immersing and stretching in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. The alkali saponification treatment described above refers to a treatment in which the cellulose ester film is immersed in a high-temperature strong alkaline solution in order to improve the wetness of the aqueous adhesive and improve the adhesiveness.
[0199]
The polarizing film, which is the main component of the polarizing plate, is an element that transmits only light having a polarization plane in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol film. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed. These are formed by forming a polyvinyl alcohol aqueous solution into a film and dyeing it by uniaxial stretching or dyeing and then uniaxially stretching, and then performing a durability treatment with a boron compound. A transparent plastic film, which is a protective film for a polarizing plate made of the cellulose ester film of the present invention, is laminated on the surface of the polarizing film to form a polarizing plate.
[0200]
The cellulose ester film obtained as described above is reduced in foreign matter failure, which is considered to be caused by the added fine particles, and is excellent in surface quality even in the case of a thin film, and has sufficient anti-blocking effect and handleability. And is useful as a protective film for optical films, particularly polarizing plates.
[0201]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these.
[0202]
Example 1
<< Preparation of solids 1-5 >>
A predetermined amount of each of the materials shown in Table 1 was put into a pressurized sealed container, heated to 80 ° C. to set the pressure in the container to 2 atm, and the cellulose ester and the plasticizer were completely dissolved while stirring. Subsequently, the solution was Azumi filter paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. Filtered using 244. After flowing this on a metal plate to evaporate the solvent, it was peeled off from the support and dried in a dryer maintained at 120 ° C. to obtain solids 1 to 5.
[0203]
[Table 1]

[0204]
CAP1 (cellulose acetate propionate): acetyl substitution degree 2.0, propionyl group substitution degree 0.8, viscosity average polymerization degree 350
CAP2 (cellulose acetate propionate): acetyl substitution degree 1.6, propionyl group substitution degree 1.2, viscosity average polymerization degree 400
CAB1 (cellulose acetate propionate): acetyl substitution degree 1.9, butyryl group substitution degree 0.7, viscosity average polymerization degree 300
TAC1 (triacetyl cellulose): degree of acetyl substitution 2.7
Plasticizer A
8 parts by mass of triphenyl phosphate (TPP)
Ethyl phthalyl ethyl glycolate (EPEG) 4 parts by mass
Solvent B
306 parts by mass of methylene chloride
34 parts by mass of ethanol
Solvent C
Methyl acetate 238 parts by mass
102 parts by mass of ethanol
(Preparation of additive solutions 1-10)
10 parts by mass of Aerosil R972V (manufactured by Nippon Aerosil Co., Ltd.) and 90 parts by mass of ethanol were stirred and mixed with a dissolver for 30 minutes as fine particles, and then dispersed with Manton Gorin to obtain a fine particle dispersion D.
[0205]
Similarly, 10 parts by mass of Aerosil 200V (manufactured by Nippon Aerosil Co., Ltd.) and 90 parts by mass of ethanol were stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton Gorin to obtain a fine particle dispersion E.
[0206]
Furthermore, as described in Table 2, any one of the above-mentioned solids 1 to 5 and / or cellulose ester and an ultraviolet absorber and a solvent are put into an additive liquid mixing tank, heated, stirred, and completely Furthermore, the fine particle dispersion was put into a tank with sufficient stirring, and the obtained mixed solution was filtered with a filter.
[0207]
[Table 2]

[0208]
UV absorber F
Ultraviolet absorber TINUVIN-326 (Ciba Specialty Chemicals Co., Ltd.) 4.0 parts by mass
Ultraviolet absorber TINUVIN-109 (Ciba Specialty Chemicals Co., Ltd.) 7.0 parts by mass
Ultraviolet absorber TINUVIN-171 (Ciba Specialty Chemicals Co., Ltd.) 7.0 parts by mass
Solvent G
100 parts by mass of methylene chloride
Solvent H
70 parts by mass of methyl acetate
15 parts by mass of ethanol
<Production of dope>
[0209]
[Table 3]

[0210]
Solvent I
306 parts by mass of methylene chloride
34 parts by mass of ethanol
Solvent J
Methyl acetate 238 parts by mass
102 parts by mass of ethanol
As shown in Table 3, cellulose ester, a plasticizer, and a solvent were placed in a sealed container, and the mixture was gradually heated while being slowly stirred, and the temperature was raised to 45 ° C. over 60 minutes and dissolved. The inside of the container was 1.2 atm. This dope was added to Azumi Filter Paper No. After filtering using 244, it left still and the bubble in dope was removed. Furthermore, the additive solution was added and mixed to obtain dopes 1 to 10.
[0211]
Each dope was sufficiently mixed by a static mixer and then cast from a die onto a stainless steel belt at a dope temperature of 25 ° C. After drying for 1 minute on a temperature-controlled stainless steel belt by contacting hot water at a temperature of 30 ° C. from the back of the stainless steel belt, and further holding 15 ° C. cold water on the back of the stainless steel belt for 15 seconds, Peeled from the stainless steel belt. The amount of residual solvent in the web at the time of peeling was 100% by mass. Next, the both ends of the peeled web were gripped with clips using a tenter, and the clip interval at both ends was changed in the width direction, so that the web was stretched 1.07 times in the width direction at 120 ° C. After the completion of stretching, the cellulose ester film having a width of 1.3 m and a film thickness of 40 μm as shown in Table 4 was obtained by drying at 125 ° C. for 10 minutes while further conveying with a roller. Visual confirmation of foreign matter failure of the obtained film
A: Zero foreign matter failure with a diameter of 10 μm or more per 100 m length of cellulose ester film
○: Less than 3 foreign matter failures with a diameter of 10 μm or more per 100 m length of cellulose ester film
Δ: The number of foreign matter failures with a diameter of 10 μm or more per 100 m length of the cellulose ester film is less than 3 to 10
×: The number of foreign matter failures of 10 μm or more per 100 m length of the cellulose ester film is 10 or more
<Roll dirt evaluation method>
After producing each 20000 m cellulose ester film, the degree of dirt on the first roll contacted with the film peeled off from the stainless steel band support was visually observed and evaluated according to the following ranks.
[0212]
A: I do not know that the roll is dirty
○: A small part of the roll is slightly dirty
Δ: The roll is slightly faintly stained
×: The roll is completely dirty
◎ ~ △ is the level at which production can continue
× indicates a level where production is interrupted and rolls need to be cleaned.
[0213]
[Table 4]

[0214]
<< Measurement of substitution degree of cellulose ester >>
It carried out according to the method prescribed | regulated to ASTM-D817-96.
[0215]
<Measurement of number average molecular weight of cellulose ester>
Measured by high performance liquid chromatography under the following conditions.
[0216]
Solvent: Acetone
Column: MPW × 1 (manufactured by Tosoh Corporation)
Sample concentration: 0.2 mass / v%
Flow rate: 1.0 ml / min
Sample injection volume: 300 μl
Standard sample: polymethyl methacrylate (Mw = 188,200)
Temperature: 23 ° C
As a result, it was confirmed that the cellulose ester films 1 to 5 of the present invention were all excellent in surface quality, with few foreign matter failures, little roll dirt, few fine dent failures in the film drying process. Moreover, generation | occurrence | production of the blocking by thin film thickness was not recognized.
[0217]
Example 2
Dope solutions 11 to 15 shown in Table 5 were prepared in the same manner as in Example 1, except that the solid material used in Example 1 was replaced with the cut product of the cellulose ester film obtained in Example 1.
[0218]
[Table 5]

[0219]
Each dope was sufficiently mixed by a static mixer and then cast from a die onto a stainless steel belt at a dope temperature of 25 ° C. After drying for 1 minute on a temperature-controlled stainless steel belt by contacting hot water at a temperature of 28 ° C. from the back surface of the stainless steel belt, and further holding cold water at 15 ° C. for 15 seconds on the back surface of the stainless steel belt, Peeled from the stainless steel belt. The amount of residual solvent in the web at the time of peeling was 100% by mass. Next, the both ends of the peeled web were gripped with clips using a tenter, and the clip interval at both ends was changed in the width direction, so that the web was stretched 1.07 times in the width direction at 120 ° C. After completion of stretching, the film was further dried at 125 ° C. for 10 minutes while being conveyed by a roller to obtain a cellulose ester film having a width of 1.3 m and a film thickness of 45 μm as shown in Table 6.
[0220]
The resulting film was visually confirmed for foreign matter failure.
A: Zero foreign matter failure with a diameter of 10 μm or more per 100 m length of cellulose ester film
○: Less than 3 foreign matter failures with a diameter of 10 μm or more per 100 m length of cellulose ester film
Δ: The number of foreign matter failures with a diameter of 10 μm or more per 100 m length of the cellulose ester film is less than 3 to 10
×: The number of foreign matter failures of 10 μm or more per 100 m length of the cellulose ester film is 10 or more
[0221]
[Table 6]

[0222]
As a result, it was confirmed that the cellulose ester films 11 to 15 of the present invention were all excellent in surface quality with few foreign matter failures, little roll dirt, few fine dent failures in the film drying process.
[0223]
Example 3
Using each of the cellulose ester films 1 to 15 obtained in Example 1 and Example 2 as a protective film for a polarizing plate, a polarizing plate was produced according to the following method, and the obtained polarizing plate was attached to a liquid crystal display, Was evaluated.
[0224]
<Production of polarizing film>
A 120 μm thick polyvinyl alcohol film was immersed in an aqueous solution containing 1 part of iodine, 2 parts of potassium iodide, and 4 parts of boric acid, and stretched 4 times at 50 ° C. to obtain a polarizing film.
[0225]
<Production of polarizing plate>
(1) As a protective film, two cellulose ester film samples cut in a longitudinal direction of 30 cm and a lateral direction of 18 cm were immersed in a 2 mol / liter sodium hydroxide solution at 50 ° C. for 2 minutes, further washed with water and dried.
[0226]
(2) The polarizing film described above adjusted to the same size as the cellulose ester film sample is immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.
[0227]
(3) Excess adhesive adhered to the polarizing film is lightly removed and placed on the B side of the cellulose ester film sample, and the B side of the other cellulose ester film sample is in contact with the adhesive. Laminate and arrange.
[0228]
(4) Excess adhesive and bubbles are removed and bonded from the end of the laminate of the polarizing film and the cellulose ester film laminated by the hand roller. The pressure of the hand roller was about 0.2 to 0.3 MPa, and the roller speed was 2 m / min.
[0229]
(5) The sample obtained in an oven at 80 ° C. was left for 2 minutes to produce a polarizing plate.
Next, the obtained polarizing plate was incorporated into a liquid crystal panel as described below, and the characteristics as a liquid crystal display device were evaluated.
[0230]
《Characteristic evaluation as a liquid crystal display device》
The polarizing plate of 15-type TFT color liquid crystal display LA-1529HM (manufactured by NEC) was peeled off, and each of the polarizing plates prepared above was cut according to the size of the liquid crystal cell. The two polarizing plates prepared as described above were bonded so as to be orthogonal to each other so that the polarizing axis of the polarizing plate did not change, with a liquid crystal cell being sandwiched, and a 15-inch TFT color liquid crystal display was prepared. When the characteristics as a polarizing plate were evaluated, when the cellulose ester films 1 to 5 and 11 to 15 of the present invention were used as a polarizing plate protective film, the visibility deteriorated due to surface quality such as foreign matter failure and film dents. This was confirmed to be excellent as a polarizing plate for an image display device such as a liquid crystal display.
[0231]
Example 4
<< Preparation of Solid 6 >>
Cellulose triacetate (acetyl substitution degree 2.88 (Fe; 0.3 ppm, Mg; 15 ppm, Ca; 26 ppm)), plasticizer, and solvent are charged in a pressurized sealed container as shown below and heated to 80 ° C. The container was heated to a pressure of 2 atm and dissolved completely with stirring. Subsequently, the solution was obtained from Azumi Filter Paper No. Filter using 260. After flowing this on a metal plate to evaporate the solvent, it was peeled off from the support and dried in a drier maintained at 120 ° C. to obtain a solid 6.
[0232]
Cellulose triacetate [acetyl substitution degree 2.88 (Fe; 0.3 ppm, Mg; 15 ppm, Ca; 26 ppm)] 100 parts by mass
Plasticizer
8 parts by mass of triphenyl phosphate (TPP)
Ethyl phthalyl ethyl glycolate (EPEG) 4 parts by mass
solvent
306 parts by mass of methylene chloride
34 parts by mass of ethanol
<< Preparation of additive liquid >>
As fine particles, 10 parts by mass of Aerosil R972V (manufactured by Nippon Aerosil Co., Ltd.) and 90 parts by mass of ethanol were stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton Gorin to obtain a fine particle dispersion.
[0233]
Furthermore, the above-mentioned solid substance 6, ultraviolet absorber and solvent are put into an additive liquid mixing tank, heated and stirred to dissolve completely, and further the fine particle dispersion is put into the tank while stirring sufficiently. The obtained liquid mixture was filtered with a filter to obtain an additive liquid.
[0234]
UV absorber
TINUVIN-326 4.0 parts by mass
(Ciba Specialty Chemicals Co., Ltd.)
TINUVIN-109 7.0 parts by mass
(Ciba Specialty Chemicals Co., Ltd.)
TINUVIN-171 7.0 parts by mass
(Ciba Specialty Chemicals Co., Ltd.)
4 parts by mass of solid 6
solvent
100 parts by mass of methylene chloride
<< Preparation of dope >>
The solid 6 and cellulose ester, plasticizer, and solvent were charged in a dissolution vessel (sealed container) in the ratios shown in Table 7 and gradually heated while slowly stirring, and the temperature was raised to 45 ° C. over 60 minutes, followed by filtration. Furthermore, the additive liquid was mixed and dope 16-20 was prepared. The respective addition amounts are as shown in Table 7.
[0235]
[Table 7]

[0236]
<< Production of film >>
Each dope was manufactured by Azumi Filter Paper No. After filtration using 260, it was cast from a die onto a stainless steel belt at a dope temperature of 25 ° C. After drying for 1 minute on a stainless steel belt whose temperature is controlled by contacting hot water at a temperature of 30 ° C. from the back surface of the stainless steel belt, and further holding cold water of 10 ° C. on the back surface of the stainless steel belt for 15 seconds, Peeled from the stainless steel belt. The amount of residual solvent in the web at the time of peeling was 100% by mass. Next, the both ends of the peeled web were gripped with clips using a tenter, and the distance between the clips at both ends was changed in the width direction, so that the web was stretched 1.07 times in the width direction at 120 ° C. with a residual solvent amount of 10 mass%. After the completion of stretching, the cellulose ester films a to e having a width of 1.3 m and a film thickness of 60 μm as shown in Table 8 were obtained by drying at 125 ° C. for 10 minutes while further conveying the rollers. The resulting film was visually confirmed for foreign matter failure.
[0237]
A: Zero foreign matter failure with a diameter of 10 μm or more per 100 m length of cellulose ester film
○: Less than 3 foreign matter failures with a diameter of 10 μm or more per 100 m length of cellulose ester film
Δ: The number of foreign matter failures with a diameter of 10 μm or more per 100 m length of the cellulose ester film is less than 3 to 10
×: The number of foreign matter failures of 10 μm or more per 100 m length of the cellulose ester film is 10 or more
Moreover, the measurement of haze and the elastic modulus were performed as follows.
[0238]
(Measurement of haze)
Measured according to ASTM-D1003-52.
[0239]
(Measurement of elastic modulus)
The cellulose ester film was allowed to stand at 23 ° C. and 55% RH for 24 hours, and then measured according to JIS K7127 under the same conditions. The sample was cut into TD direction (width direction) 10 mm × MD direction (longitudinal direction) 200 mm or MD direction 10 mm × TD direction 200 mm, and the tensile speed was 100 mm / min and the distance between marked lines was 100 mm.
[0240]
[Table 8]

[0241]
As a result, it was confirmed that the cellulose ester films b to e of the present invention had few foreign matter failures and a film having excellent surface quality was obtained. Further, it was revealed that the modulus of elasticity was also high, and the cellulose ester film of the present invention was found to be a higher performance film than conventional.
[0242]
【Effect of the invention】
As demonstrated in the Examples, the solids for preparing the cellulose ester solution according to the present invention, the cellulose ester solution, the method for producing the cellulose ester film, the cellulose ester film, the polarizing plate and the display device using the same are fine particles or the cellulose ester itself. The object is to remarkably reduce defects derived from agglomeration, and in particular, it has an excellent effect on the surface quality of the cellulose ester film.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a slit die used in the manufacturing method of the present invention.
[Explanation of symbols]
1 Casting entrance
2 slits
3 Slit

Claims (4)

  A solid for preparing a cellulose ester solution containing fine particles, wherein cellulose ester and a plasticizer are dissolved and mixed in an organic solvent and then dried.   A solid for preparing a cellulose ester solution containing fine particles, wherein cellulose ester and a plasticizer are dissolved and mixed in an organic solvent, the solution is filtered, and then dried to a solvent content of less than 10% by mass.   A solid for preparing a cellulose ester solution containing fine particles, wherein cellulose ester and a plasticizer are dissolved in an organic solvent, the solution is filtered, and then dried to a solvent content of less than 10% by mass at 70 to 160 ° C. .   The solid for preparing a cellulose ester solution containing fine particles according to any one of claims 1 to 3, wherein a cellulose ester having a total content of Ca, Mg and Fe of 100 ppm or less is used.

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