JP4052444B2 - Optical disc substrate - Google Patents

Description

【００１３】
本発明において、「精密転写性」とは、熱可塑性樹脂成形材料を用いて射出成形法（射出圧縮成形法を含む）などによって光ディスク基板を製造する場合に、スタンパーに刻印された微細な凹凸形状を忠実に転写することができる性質のことである。
【００１４】
そもそも、射出成形法（射出圧縮成形法を含む）などによって光ディスク基板を製造する場合に、基板表面に形成される微細な凹凸形状は、金型キャビティ内に充填された樹脂が加圧されることで、該凹凸形状を反転したパターンが予め刻印されているスタンパーの溝に入り込み、次いで一定時間保持された後に冷却固化して形成される。このスキームの中でキャビティに充填される樹脂は金型壁面（スタンパー面）と接触した直後から熱を奪われる。その結果、基板表面には時間経過と共に発達する冷却固化層が形成される。また、基板内部においても冷却が進行して樹脂温度が低下することによる粘度上昇が起こる。
【００１５】
本発明者らは実験によって、▲１▼転写精度は金型キャビティ内への樹脂の充填が完了した直後に基板表面付近に形成される冷却固化層の変形性と該固化層を変形させる圧力の伝達性によって左右されること、▲２▼成形プロセスの中で転写が起こる時点の樹脂表面状態と考えられる転移域〜ガラス域の弾性率が低い材料を用いると高転写率の光ディスク基板が提供されること、などを見出した。そして、主たる二価フェノール成分が１,１−ビス（４−ヒドロキシフェニル）プロパンである芳香族ポリカーボネート樹脂（以後、ＢｉｓＰ−ＰＲＤ系樹脂と称する）よりなる光学用成形材料を用いて成形された光ディスク基板は高転写率を示すことが判明した。しかも、ＢｉｓＰ−ＰＲＤ系樹脂製の光ディスク基板は高能率で得られるものである。
【００１６】
また本発明によれば、ＢｉｓＰ−ＰＲＤ系樹脂は吸水率が極めて低く、該樹脂よりなる光学用成形材料を用いて成形された光ディスク基板は吸湿による反り変化が小さいことも判明した。
【００１７】
本発明で提供されるＢｉｓＰ−ＰＲＤ系樹脂は、１,１−ビス（４−ヒドロキシフェニル）プロパンとカーボネート前駆体とを溶液重合法または溶融重合法によって反応させることによって製造することができる。
【００２０】
カーボネート前駆体としてはカルボニルハライド、カーボネートエステルまたはハロホルメート等が使用され、具体的にはホスゲン、ジフェニルカーボネートまたは二価フェノールのジハロホルメート等が挙げられるが、ホスゲンまたはジフェニルカーボネートが好ましい。
【００２１】
上記二価フェノールとカーボネート前駆体を例えば溶液重合法または溶融重合法等によって反応させてポリカーボネート樹脂を製造するに当っては、必要に応じて触媒、末端停止剤、二価フェノールの酸化防止剤等を使用してもよい。
【００２２】
溶液重合法による反応は、二価フェノールとホスゲンとの反応であり、通常、酸結合剤および有機溶媒の存在下に行われる。酸結合剤としては、例えば水酸化ナトリウム、水酸化カリウム等のアルカリ金属水酸化物、またはピリジン等のアミン化合物が用いられる。有機溶媒としては、例えば塩化メチレン、クロロベンゼン等のハロゲン化炭化水素が用いられる。また反応促進のために、例えばトリエチルアミン、テトラ−ｎ−ブチルアンモニウムブロマイド、テトラ−ｎ−ブチルホスホニウムブロマイド等の第三級アミン、第四級アンモニウム化合物、第四級ホスホニウム化合物等の触媒を用いることもできる。その際、反応温度は０〜４０℃程度、反応時間は１０分〜５時間程度、反応中のｐＨは９以上に保つのが好ましい。
【００２３】
重合反応においては、通常末端停止剤が使用される。かかる末端停止剤としては単官能フェノール類を使用することができる。単官能フェノール類は、末端停止剤として分子量調節のために一般的に使用され、かくして得られたポリカーボネート樹脂は末端が単官能フェノール類に基づく基によって封鎖されているため、未封鎖のものと比べて熱安定性に優れている。かかる単官能フェノール類としては、一般にはフェノールまたは低級アルキル置換フェノールであって、下記式［２］
【００２４】
【化３】

【００２５】
［式中、Ａは水素原子または炭素数１〜９の直鎖または分岐のアルキル基あるいはフェニル置換アルキル基であり、ｒは１〜５、好ましくは１〜３の整数である。］
で表される単官能フェノール類を示すことができる。
【００２６】
上記単官能フェノール類の具体例としては、例えばフェノール、ｐ−ｔｅｒｔ−ブチルフェノール、ｐ−クミルフェノールおよびイソオクチルフェノールが挙げられる。
【００２７】
また、他の単官能フェノール類として、長鎖のアルキル基あるいは脂肪族エステル基を置換基として有するフェノール類または安息香酸クロライド類、もしくは長鎖のアルキルカルボン酸クロライド類を使用することができる。これらはポリカーボネート樹脂の末端を封鎖し分子量調節剤として機能するのみならず、該樹脂の溶融流動性を向上せしめ、成形加工性を向上せしめる他、基板としての物性、とりわけ樹脂の吸水率を低くする効果があり、また基板の複屈折率も低減し得る効果もあり、好ましく使用される。なかでも、下記式［３］および［４］
【００２８】
【化４】

【００２９】
【化５】

【００３０】
［式中、Ｘは−Ｒ−Ｏ−、−Ｒ−ＣＯ−Ｏ−または−Ｒ−Ｏ−ＣＯ−である。ここでＲは単結合または炭素数１〜１０、好ましくは１〜５の二価の脂肪族炭化水素基を示し、ｎは１０〜５０の整数を示す。］
で表される長鎖のアルキル基を置換基として有するフェノール類が好ましく使用される。
【００３１】
前記式［３］の置換フェノール類としては、ｎが１０〜３０、特に１０〜２６のものが好ましく、その具体例としては、例えばデシルフェノール、ドデシルフェノール、テトラデシルフェノール、ヘキサデシルフェノール、オクタデシルフェノール、エイコシルフェノール、ドコシルフェノールおよびトリアコンチルフェノール等が挙げられる。
【００３２】
また、前記式［４］の置換フェノール類としてはＸが−Ｒ−ＣＯ−Ｏ−であり、Ｒが単結合である化合物が適当であり、ｎが１０〜３０、特に１０〜２６のものが好適であって、その具体例としては、例えばヒドロキシ安息香酸デシル、ヒドロキシ安息香酸ドデシル、ヒドロキシ安息香酸テトラデシル、ヒドロキシ安息香酸ヘキサデシル、ヒドロキシ安息香酸エイコシル、ヒドロキシ安息香酸ドコシルおよびヒドロキシ安息香酸トリアコンチルが挙げられる。
【００３３】
これらの末端停止剤は、得られたポリカーボネート樹脂の全末端に対して、少くとも５モル％、好ましくは少くとも１０モル％導入されることが望ましく、また、末端停止剤は単独でまたは２種以上混合して使用してもよい。
【００３４】
溶融重合法による反応は、通常二価フェノールとカーボネートエステルとのエステル交換反応であり、不活性ガスの存在下に二価フェノールとカーボネートエステルとを加熱しながら混合して、生成するアルコールまたはフェノールを留出させる方法により行われる。反応温度は生成するアルコールまたはフェノールの沸点等により異なるが、通常１２０〜３５０℃の範囲である。反応後期には反応系を１０〜０.１Ｔｏｒｒ（１.３〜０.０１３×１０³Ｐａ）程度に減圧して生成するアルコールまたはフェノールの留出を容易にさせる。反応時間は通常１〜４時間程度である。
【００３５】
カーボネートエステルとしては、置換されていてもよい炭素数６〜１０のアリール基、アラルキル基あるいは炭素数１〜４のアルキル基などのエステルが挙げられる。具体的にはジフェニルカーボネート、ジトリルカーボネート、ビス（クロロフェニル）カーボネート、ｍ―クレジルカーボネート、ジナフチルカーボネート、ビス（ジフェニル）カーボネート、ジメチルカーボネート、ジエチルカーボネート、ジブチルカーボネートなどが挙げられ、なかでもジフェニルカーボネートが好ましい。
【００３６】
また、重合速度を高めるために重合触媒を用いることができ、かかる重合触媒としては、例えば水酸化ナトリウム、水酸化カリウム、二価フェノールのナトリウム塩、カリウム塩等のアルカリ金属化合物；水酸化カルシウム、水酸化バリウム、水酸化マグネシウム等のアルカリ土類金属化合物；テトラメチルアンモニウムヒドロキシド、テトラエチルアンモニウムヒドロキシド、トリメチルアミン、トリエチルアミン等の含窒素塩基性化合物；アルカリ金属やアルカリ土類金属のアルコキシド類；アルカリ金属やアルカリ土類金属の有機酸塩類；その他に亜鉛化合物類、ホウ素化合物類、アルミニウム化合物類、珪素化合物類、ゲルマニウム化合物類、有機スズ化合物類、鉛化合物類、オスミウム化合物類、アンチモン化合物類、マンガン化合物類、チタン化合物類、ジルコニウム化合物類などの通常エステル化反応、エステル交換反応に使用される触媒を用いることができる。触媒は単独で使用してもよいし、２種以上組み合わせて使用してもよい。これらの重合触媒の使用量は、原料の二価フェノール１モルに対し、好ましくは１×１０^-8〜１×１０^-3当量、より好ましくは１×１０^-7〜５×１０^-4当量の範囲で選ばれる。
【００３７】
また、かかる重合反応において、フェノール性の末端基を減少するために、重合反応の後期あるいは終了後に、例えばビス（クロロフェニル）カーボネート、ビス（ブロモフェニル）カーボネート、ビス（ニトロフェニル）カーボネート、ビス（フェニルフェニル）カーボネート、クロロフェニルフェニルカーボネート、ブロモフェニルフェニルカーボネート、ニトロフェニルフェニルカーボネート、フェニルフェニルカーボネート、メトキシカルボニルフェニルフェニルカーボネートおよびエトキシカルボニルフェニルフェニルカーボネート等の化合物を加えることが好ましい。なかでも２−クロロフェニルフェニルカーボネート、２−メトキシカルボニルフェニルフェニルカーボネートおよび２−エトキシカルボニルフェニルフェニルカーボネートが好ましく、特に２−メトキシカルボニルフェニルフェニルカーボネートが好ましく使用される。
【００３８】
本発明で提供される光ディスク基板の原料樹脂となるＢｉｓＰ−ＰＲＤ系樹脂は、２３℃の純水に浸漬した場合の飽和吸水率が０.２５重量％以下であることが好ましく、０.２０重量％以下であることがより好ましい。飽和吸水率が０.２５重量％を超えると、吸湿および脱湿過程において光ディスクの反り変形が生じ易くなり、フォーカスエラーやトラッキングエラーなどを起こし易くなるので好ましくない。光ディスクの吸湿および脱湿過程における反り変形に関しては以下の測定法を用いた。すなわち、ディスクを温度３０℃、湿度９０％ＲＨの環境（Ａ環境）下で飽和吸水率に達するまで暴露した後、温度２３℃、湿度５０％ＲＨの環境（Ｂ環境）下に移した時に生じる中心から５８ｍｍ部のチルト（Ｔｉｌｔ）変化を経時的に測定し、チルト（Ｔｉｌｔ）変化の最大値と定常に達したときの値の差（△Ｔｉｌｔ）を比較したものである。このときのディスクの△Ｔｉｌｔは０.９度以内、好ましくは０.７５度以内、さらに好ましくは０.５度以内である。
【００３９】
本発明で提供される光ディスク基板の原料樹脂であるＢｉｓＰ−ＰＲＤ系樹脂は、従来公知の方法（溶液重合法、溶融重合法等）により製造した後、溶液状態において濾過処理を行ない、不純物や異物を徹底的に除去することが好ましい。さらに、射出成形（射出圧縮成形を含む）に供するためのペレット状ポリカーボネート樹脂を得る押出工程（ペレット化工程）においても、溶融状態の時に、焼結金属フィルターを通すなどして異物を除去することが好ましい。該フィルターとしては濾過精度１０μｍのものが好ましく使用される。また必要により、例えば、リン原子を含む酸化防止剤などの添加剤を加えることも好ましい。いずれにしても射出成形（射出圧縮成形を含む）前の原料樹脂は異物、不純物、溶媒などの含有量を極力低くしておくことが必要である。
【００４０】
前記ＢｉｓＰ−ＰＲＤ系樹脂より光ディスク基板を製造する場合には、通常、射出成形機（射出圧縮成形機を含む）を用いる。該成形機は一般的に使用されているものでよいが、炭化物の発生を抑制し、ディスク基板の信頼性を高める観点からシリンダーやスクリューと樹脂との付着性が低く、且つ、耐食性・耐摩耗性を示す材料を使用してなるものを用いることが好ましい。成形工程の環境は、本発明の目的から考えて、可能な限りクリーンであることが好ましい。また、成形に供する材料を十分乾燥して水分を除去することや、溶融樹脂の分解を招くような滞留を起こさないように配慮することも重要となる。
【００４１】
かくして成形された光ディスク基板は、ＤＶＤ（Ｄｉｇｉｔａｌ Ｖｅｒｓａｔｉｌｅ Ｄｉｓｃ）など現行の光ディスクはもちろん、ＢＤ（Ｂｌｕ−ｒａｙ Ｄｉｓｃ）やＨＤ−ＤＶＤ−ＲＡＭ等で代表される高密度光ディスク用基板としても好適に使用される。
【００４２】
本発明の光ディスク基板は、原料となるＢｉｓＰ−ＰＲＤ系樹脂の精密転写性が極めて優れているので、ピット列もしくはグルーブ列の間隔が０.１〜０.８μｍ、好ましくは０.１〜０.５μｍ、さらに好ましくは０.１〜０.３５μｍである光ディスク基板を、従来の成形法によって、容易に得ることが可能となる。またグルーブもしくはピットの光学的深さが、記録再生に使用されるレーザー光の波長λと基板の屈折率ｎに対してλ／８ｎ〜λ／２ｎ、好ましくはλ／６ｎ〜λ／２ｎ、さらに好ましくはλ／４ｎ〜λ／２ｎの範囲にある光ディスク基板を得ることができる。かくして、１００Ｇｂｉｔ／ｉｎｃｈ²以上の記録密度を有する光ディスクの基板も容易に提供することができる。
【００４３】
【実施例】
以下、実施例を挙げて本発明を詳細に説明するが、本発明はその趣旨を超えない限り、何らこれに限定されるものではない。実施例または比較例において「部」は重量部を示す。なお、各種樹脂の物性測定、該樹脂を用いた光ディスク基板の成形・評価は以下の方法に従った。
【００４４】
（１）ガラス転移温度
ＴＡインスツルメント社製の熱分析システム ＤＳＣ−２９１０を使用して、窒素雰囲気下（窒素流量：４０ｍｌ／ｍｉｎ）・昇温速度：２０℃／ｍｉｎの条件下で測定した。
【００４５】
（２）貯蔵弾性率
レオメトリック社製の動的粘弾性測定装置 ＲＤＡIIを使用して、周波数８９.７ｒａｄ／ｓｅｃ・降温速度２℃／ｍｉｎの条件下で、ゴム域〜ガラス域におけるずり貯蔵弾性率の温度依存性を測定した。表１に記載の値は、該温度依存性曲線からＴｇ’−５℃における値を読み取ったものである。ここで、「Ｔｇ’−５℃」の「Ｔｇ’」はずり貯蔵弾性率（Ｇ’）と同時に測定されるずり損失弾性率（Ｇ”）の温度依存性曲線から得た力学的ガラス転移温度を示す。
【００４６】
（３）吸水率
ＡＳＴＭ Ｄ−５７０に従い、φ４５ｍｍ成形プレートを水中浸漬し重量変化率（重量％）により求めた。
【００４７】
（４）転写性
日精樹脂工業製の射出成形機 ＭＯ４０Ｄ−３Ｈ、深さ２００ｎｍ・間隔０.５μｍ・幅０.２μｍの溝が刻まれたスタンパーを用いて、直径１２０ｍｍ・厚み０.６ｍｍの光ディスク基板を成形した。なお、シリンダー温度は３６０℃の一定とし、金型温度を表１に記載の通り各樹脂ごとに設定した。
【００４８】
上記基板にスタンパーから転写された溝の深さを、原子間力顕微鏡（セイコー電子工業 ＳＰＩ−３７００）を用いて、該基板の半径４０ｍｍの位置にて５ヶ所を測定した。各樹脂の転写性は次式で示される転写率として表した。この値が大きいほど転写性が優れている。
転写率（％）＝ １００ × ［基板の溝深さ／スタンパーの溝深さ］
【００４９】
（５）ΔＴｉｌｔ
日精樹脂工業製の射出成形機 ＭＯ４０Ｄ−３Ｈを用いて、各ペレットから直径１２０ｍｍ・厚み１.２ｍｍの光ディスク基板を射出成形した。次いで、該基板に反射膜、誘電体層１、相変化記録膜、誘電体層２を順にスパッタ蒸着させ、その上にポリカーボネート製薄膜カバー層を貼り合わせ光ディスクを得た。
【００５０】
上記光ディスクを温度３０℃、湿度９０％ＲＨの環境（Ａ環境）下で飽和吸水率に達するまで暴露した後、温度２３℃、湿度５０％ＲＨの環境（Ｂ環境）下に移した。その後、環境変化によって生じる中心から５８ｍｍ部のＴｉｌｔ変化をジャパン・イー・エム製の３次元形状測定器ＤＬＤ−３０００Ｕにより経時的に測定し、Ｔｉｌｔ変化が最大に達した値および定常に達した値の差を△Ｔｉｌｔとした。
【００５１】
［実施例１］
温度計、撹拌機および還流冷却器の付いた反応器に、４８％水酸化ナトリウム水溶液４９．２部およびイオン交換水３５７．６部を仕込み、これに１,１−ビス（４−ヒドロキシフェニル）プロパン４５．３部、ハイドロサルファイト０.０９部を溶解した後、塩化メチレン２０２．６部を加え、撹拌下、１５〜２５℃でホスゲン２３．６部を約４０分かけて吹き込んだ。ホスゲンの吹き込み終了後、４８％水酸化ナトリウム水溶液１６.４部およびｐ−ｔｅｒｔ−ブチルフェノール１.８９部を加え、撹拌を再開、乳化後トリエチルアミン０.０７部を加え、さらに２８〜３３℃で１時間撹拌して反応を終了した。反応終了後生成物を塩化メチレンで希釈して水洗した後、塩酸酸性にして水洗し、さらに水相の導電率がイオン交換水とほぼ同じになるまで水洗を繰り返し、ポリカーボネート樹脂の塩化メチレン溶液を得た。次いで、この溶液を目開き０.３μｍのフィルターに通過させ、さらに軸受け部に異物取出口を有する隔離室付きニーダー中の温水に滴下、塩化メチレンを留去しながらポリカーボネート樹脂をフレーク化し、引続き該含液フレークを粉砕・乾燥してパウダーを得た。その後、該パウダーにトリス（２,４−ｄｉ−ｔｅｒｔ−ブチルフェニル）ホスファイトを０.００２５重量％、ステアリン酸モノグリセリドを０.０５重量％添加し、均一に混合した後、かかるパウダーをベント式二軸押出機［神戸製鋼（株）製ＫＴＸ−４６］により脱気しながら溶融混練し、ポリカーボネート樹脂のペレットを得た。該ペレットのガラス転移温度、貯蔵弾性率、吸水率、光弾性定数を表１に掲載した。
【００５２】
該ペレットから、射出成形機（日精樹脂工業 ＭＯ４０Ｄ−３Ｈ）、キャビティ厚０.６ｍｍｔ・直径１２０ｍｍの金型、深さ２００ｎｍ・間隔０.５μｍ・幅０.２μｍの溝が刻まれたスタンパーを用い、シリンダー設定温度３６０℃、金型温度１１９℃、充填時間０.２秒、冷却時間１５秒、型締力４０トンの条件で光ディスク基板を成形した。この時の転写性評価結果も表１に併記した。
【００５３】
［比較例１］
２,２−ビス（４−ヒドロキシフェニル）プロパンより得られたポリカーボネート樹脂（帝人化成製パンライト ＡＤ−５５０３）を用い、金型温度を１１２℃とした以外は実施例１と同様にして基板成形を行い、該基板の転写性を評価した。この時の転写性評価結果を樹脂物性とともに表１に記載した。
【００５４】
【発明の効果】
本発明によれば、光ディスク、とりわけ高密度光ディスクの基板を射出成形法などにより製造する場合に、スタンパー上に予め刻印された凹凸形状が正確に転写されており（高転写率）、且つ、吸水による反り変形が小さい光ディスク基板を提供することが可能となり、その奏する効果は格別なものである。
【００５５】
【表１】

注．ΔT＝ガラス転移温度と金型温度との差＝Tg−Tmo[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk substrate molded using an optical molding material made of an aromatic polycarbonate resin having excellent processability and low water absorption. More specifically, the present invention relates to an optical disc substrate having a high transfer rate and less warpage in the field of optical discs such as DVD (Digital Versatile Disc) and BD (Blu-ray Disc). In particular, the present invention relates to a substrate for a high-density optical disk having a very large recording capacity.
[0002]
[Prior art]
In recent years, the recording density of optical discs has been steadily improved, and a capacity of 4.7 GB has been realized in DVD-R, DVD-RW, and DVD-RAM that can be recorded / reproduced recently, including a read-only DVD-ROM. It was. Also, MO disks with a capacity of 5.2 GB on both sides and a diameter of 5.25 "with a capacity of 1.3 GB on one side are already on the market. However, along with the advancement of information technology, the market development of the optical disc field is remarkable, and in the future, high-density optical discs capable of recording a huge amount of information are expected to appear. For example, an optical disc having a recording density of 100 Gbit / inch ² or higher that can support digital high-quality broadcasting and the like is also desired.
[0003]
Increasing the density of the optical disk is usually achieved by increasing the density of the grooves by, for example, reducing the interval between pits and grooves formed on the substrate of the disk. For example, in increasing the density from CD to DVD, measures are taken to increase the recording density in the track direction by narrowing the track pitch from 1.6 μm to 0.74 μm.
[0004]
An optical disk substrate is manufactured by injection molding (including injection compression molding) of a thermoplastic resin. At that time, a fine uneven shape that becomes a source of a recording / reproducing signal pre-engraved on the stamper is formed on the substrate surface from the stamper. Transcribed. Therefore, how accurately the uneven shape can be transferred when forming a substrate, that is, precise transferability is important. In particular, this importance becomes significant in the formation of a substrate for a high-density optical disk. In a high-density optical disk, in addition to being made of a substrate with a high transfer rate, it is extremely important in practice that the warpage deformation of the substrate due to environmental changes (for example, moisture absorption) is small. This is because if the substrate warps greatly, the reflection angle of the laser beam increases, which causes undesirable problems such as signal reading errors. In particular, during drive operation, the temperature inside the machine is high and the humidity is low. Therefore, a rapid change is likely to occur, and a focus error such as a signal being unreadable due to deformation of the disk is likely to occur.
[0005]
By the way, as a substrate material such as CD (compact disc), MO (magneto-optical disc), DVD (Digital Versatile Disk), etc., it has many excellent properties such as transparency, heat resistance, impact resistance and the like. Polycarbonate resin obtained by reacting phosgene or diphenyl carbonate with 2-bis- (4-hydroxyphenyl) propane (common name: bisphenol A) (hereinafter referred to as BisP-A resin) has been widely used. It was.
[0006]
However, recently, as the density has been increased as described above, an optical disk substrate formed from a BisP-A resin having an excellent balance of physical properties has not been sufficiently satisfactory in terms of precision transferability and warpage. In high-density optical disks with extremely large recording capacities that will appear in the future, it is clear that the groove width and the pitch interval between grooves will become narrower, the groove gradient will become steeper, and the substrate will become thinner. is there. Therefore, it is obvious that it is extremely difficult to obtain a substrate having a high transfer rate and a low warpage by using the BisP-A resin, and the improvement thereof is necessary.
[0007]
In order to meet the demand for improvement in transferability, various studies have been made so far from both sides of molding technology and material modification. As for the former, for example, it has been confirmed that a method of setting the cylinder temperature and the mold temperature at the time of substrate molding high is effective. However, since this method is a high-temperature molding, the cooling time in the mold must be lengthened, which causes a problem that the molding cycle is extended and the productivity is poor. If molding is performed with a high cycle forcibly, a mold release failure occurs when the substrate is taken out of the mold, and the pits and grooves are deformed. On the contrary, there arises a problem that the transfer accuracy is lowered. As for the latter, for example, a method of containing a large amount of low molecular weight in a polycarbonate resin (JP-A-9-208684, JP-A-11-1551), or a method of using a specific long-chain alkylphenol as a terminal terminator (Japanese Patent Laid-Open No. 11-269260) has been proposed. However, the above method generally leads to a decrease in the thermal stability of the resin, and the resin is thermally decomposed during molding, so that the mechanical strength of the obtained substrate is significantly reduced, the substrate is cracked when the substrate is ejected from the mold, In addition, when handling the final product optical disc, there is a drawback such as damage. As described above, all of the conventional techniques aim to improve transferability by improving the fluidity of the resin, but a substrate that can withstand practical use has not been obtained with high efficiency. Furthermore, when the optical disk substrate is formed, the mechanism by which the transfer occurs is not clarified, and there remains room for reconsideration in terms of essential points.
[0008]
On the other hand, in response to the demand for suppressing water absorption deformation, for example, in Japanese Patent Application Laid-Open No. 2000-11449, “a substrate, a recording layer arranged on this substrate for recording an information signal, and a laminate on the recording layer” The disk-shaped information recording medium has a transparent protective layer and records / reproduces information signals by making light incident from the transparent protective layer side. The substrate includes a resin-made core layer and a core layer. An information recording medium comprising: a surface layer made of a resin that has an irregularity of information signals on the recording layer side on one side and has fluidity compared to the core layer In other words, a substrate using a resin having a water absorption rate of 0.3% or less on the substrate surface layer has been proposed, and a method for solving the problem with a complicated substrate configuration such as two-color molding or sandwich molding is disclosed.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical disk substrate, particularly a high-density optical disk substrate, which has a high transfer rate and a small amount of warping deformation.
[0010]
As a result of intensive research aimed at achieving the above object, the present inventors have used a material made of an aromatic polycarbonate resin having a specific structure as a molding material, so that the optical disk substrate has a high transfer rate and does not warp even with a simple configuration. It was found that can be obtained. The present invention has been completed based on this finding.
[0011]
[Means for Solving the Problems]
Hereinafter, the present invention will be described in detail. According to the present invention, the dihydric phenol component is molded using an optical molding material made of an aromatic polycarbonate resin which is 1,1-bis (4-hydroxyphenyl) propane represented by the following formula [1]. An optical disc substrate is provided.
[0012]
[Chemical 2]

[0013]
In the present invention, “precise transferability” means a fine uneven shape stamped on a stamper when an optical disk substrate is manufactured by an injection molding method (including an injection compression molding method) using a thermoplastic resin molding material. It is a property that can be transferred faithfully.
[0014]
In the first place, when manufacturing an optical disk substrate by injection molding (including injection compression molding), etc., the fine uneven shape formed on the substrate surface is that the resin filled in the mold cavity is pressurized. Then, a pattern having the concavo-convex shape reversed is formed in a groove of a stamper stamped in advance, and is then cooled and solidified after being held for a predetermined time. In this scheme, the resin filled in the cavity is deprived of heat immediately after coming into contact with the mold wall surface (stamper surface). As a result, a cooled and solidified layer that develops over time is formed on the substrate surface. Also, the viscosity increases due to the cooling inside the substrate and the resin temperature decreasing.
[0015]
Through experiments, the present inventors have determined that (1) transfer accuracy is determined by the deformability of the cooled solidified layer formed near the substrate surface immediately after the resin filling into the mold cavity is completed and the pressure for deforming the solidified layer. (2) High transfer rate optical disk substrate can be provided by using a material having a low elastic modulus in the transition region to the glass region, which is considered to be the resin surface state at the time of transfer during the molding process. I found out. An optical disk molded using an optical molding material made of an aromatic polycarbonate resin whose main dihydric phenol component is 1,1-bis (4-hydroxyphenyl) propane (hereinafter referred to as BisP-PRD resin). The substrate was found to exhibit a high transfer rate. In addition, an optical disk substrate made of BisP-PRD resin can be obtained with high efficiency.
[0016]
Further, according to the present invention, it has also been found that the BisP-PRD resin has an extremely low water absorption rate, and the optical disk substrate molded using the optical molding material made of the resin has a small warp change due to moisture absorption.
[0017]
The BisP-PRD resin provided in the present invention can be produced by reacting 1,1-bis (4-hydroxyphenyl) propane and a carbonate precursor by a solution polymerization method or a melt polymerization method.
[0020]
As the carbonate precursor, carbonyl halide, carbonate ester, haloformate or the like is used, and specifically, phosgene, diphenyl carbonate, dihaloformate of dihydric phenol, or the like can be mentioned, but phosgene or diphenyl carbonate is preferable.
[0021]
In producing a polycarbonate resin by reacting the dihydric phenol with a carbonate precursor by, for example, a solution polymerization method or a melt polymerization method, a catalyst, a terminal terminator, a dihydric phenol antioxidant, etc., as necessary. May be used.
[0022]
The reaction by the solution polymerization method is a reaction between a dihydric phenol and phosgene, and is usually performed in the presence of an acid binder and an organic solvent. As the acid binder, for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an amine compound such as pyridine is used. As the organic solvent, for example, halogenated hydrocarbons such as methylene chloride and chlorobenzene are used. In order to accelerate the reaction, a catalyst such as a tertiary amine such as triethylamine, tetra-n-butylammonium bromide or tetra-n-butylphosphonium bromide, a quaternary ammonium compound or a quaternary phosphonium compound may be used. it can. At that time, the reaction temperature is preferably about 0 to 40 ° C., the reaction time is about 10 minutes to 5 hours, and the pH during the reaction is preferably maintained at 9 or more.
[0023]
In the polymerization reaction, a terminal terminator is usually used. As such a terminal terminator, monofunctional phenols can be used. Monofunctional phenols are generally used as end terminators for molecular weight control, and the polycarbonate resins thus obtained are blocked with groups based on monofunctional phenols, so that they are compared with unblocked ones. Excellent thermal stability. Such monofunctional phenols are generally phenols or lower alkyl-substituted phenols having the following formula [2]
[0024]
[Chemical 3]

[0025]
[Wherein, A is a hydrogen atom, a linear or branched alkyl group having 1 to 9 carbon atoms or a phenyl-substituted alkyl group, and r is an integer of 1 to 5, preferably 1 to 3. ]
The monofunctional phenol represented by these can be shown.
[0026]
Specific examples of the monofunctional phenols include phenol, p-tert-butylphenol, p-cumylphenol and isooctylphenol.
[0027]
In addition, as other monofunctional phenols, phenols or benzoic acid chlorides having a long chain alkyl group or an aliphatic ester group as a substituent, or long chain alkyl carboxylic acid chlorides can be used. These not only block the ends of the polycarbonate resin and function as a molecular weight regulator, but also improve the melt fluidity of the resin and improve molding processability, and lower the physical properties of the substrate, especially the water absorption rate of the resin. It is effective and has an effect of reducing the birefringence of the substrate, and is preferably used. Among these, the following formulas [3] and [4]
[0028]
[Formula 4]

[0029]
[Chemical formula 5]

[0030]
[Wherein, X represents —R—O—, —R—CO—O— or —R—O—CO—. Here, R represents a single bond or a divalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 5 carbon atoms, and n represents an integer of 10 to 50. ]
Phenols having a long-chain alkyl group represented by the formula as a substituent are preferably used.
[0031]
As the substituted phenols of the formula [3], those having n of 10 to 30, particularly 10 to 26 are preferable, and specific examples thereof include decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, and the like. , Eicosylphenol, docosylphenol, triacontylphenol and the like.
[0032]
Further, as the substituted phenols of the above formula [4], those in which X is —R—CO—O— and R is a single bond are suitable, and those in which n is 10 to 30, particularly 10 to 26. Specific examples thereof include, for example, decyl hydroxybenzoate, dodecyl hydroxybenzoate, tetradecyl hydroxybenzoate, hexadecyl hydroxybenzoate, eicosyl hydroxybenzoate, docosyl hydroxybenzoate and triacontyl hydroxybenzoate.
[0033]
These end terminators are desirably introduced in an amount of at least 5 mol%, preferably at least 10 mol%, based on the total terminals of the obtained polycarbonate resin. You may mix and use above.
[0034]
The reaction by the melt polymerization method is usually a transesterification reaction between a dihydric phenol and a carbonate ester. In the presence of an inert gas, the dihydric phenol and the carbonate ester are mixed with heating, and the resulting alcohol or phenol is mixed. It is carried out by a distilling method. The reaction temperature varies depending on the boiling point of the alcohol or phenol produced, but is usually in the range of 120 to 350 ° C. In the latter stage of the reaction, the reaction system is reduced in pressure to about 10 to 0.1 Torr (1.3 to 0.013 × 10 ³ Pa) to facilitate the distillation of the alcohol or phenol produced. The reaction time is usually about 1 to 4 hours.
[0035]
Examples of the carbonate ester include esters such as an optionally substituted aryl group having 6 to 10 carbon atoms, an aralkyl group, or an alkyl group having 1 to 4 carbon atoms. Specific examples include diphenyl carbonate, ditolyl carbonate, bis (chlorophenyl) carbonate, m-cresyl carbonate, dinaphthyl carbonate, bis (diphenyl) carbonate, dimethyl carbonate, diethyl carbonate, and dibutyl carbonate. Is preferred.
[0036]
In order to increase the polymerization rate, a polymerization catalyst can be used. Examples of the polymerization catalyst include alkali metal compounds such as sodium hydroxide, potassium hydroxide, sodium salt of dihydric phenol, potassium salt; calcium hydroxide, Alkaline earth metal compounds such as barium hydroxide and magnesium hydroxide; nitrogen-containing basic compounds such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylamine and triethylamine; alkoxides of alkali metals and alkaline earth metals; alkali metals And organic acid salts of alkaline earth metals; other zinc compounds, boron compounds, aluminum compounds, silicon compounds, germanium compounds, organotin compounds, lead compounds, osmium compounds, antimony compounds, manganese Conversion Things, titanium compounds, usually the esterification reaction, such as zirconium compounds, there can be used a catalyst used in the transesterification reaction. A catalyst may be used independently and may be used in combination of 2 or more type. The amount of these polymerization catalysts used is preferably 1 × 10 ⁻⁸ to 1 × 10 ⁻³ equivalents, more preferably 1 × 10 ^{−7 to} 5 × 10 ⁻⁴ equivalents, relative to 1 mole of dihydric phenol as a raw material. Selected by range.
[0037]
Further, in this polymerization reaction, in order to reduce phenolic end groups, for example, bis (chlorophenyl) carbonate, bis (bromophenyl) carbonate, bis (nitrophenyl) carbonate, bis (phenyl) is used at a later stage or after completion of the polymerization reaction. It is preferable to add compounds such as (phenyl) carbonate, chlorophenyl phenyl carbonate, bromophenyl phenyl carbonate, nitrophenyl phenyl carbonate, phenylphenyl carbonate, methoxycarbonylphenyl phenyl carbonate and ethoxycarbonylphenyl phenyl carbonate. Of these, 2-chlorophenyl phenyl carbonate, 2-methoxycarbonylphenyl phenyl carbonate and 2-ethoxycarbonylphenyl phenyl carbonate are preferable, and 2-methoxycarbonylphenyl phenyl carbonate is particularly preferably used.
[0038]
The BisP-PRD resin used as the raw material resin for the optical disk substrate provided by the present invention preferably has a saturated water absorption of 0.25% by weight or less when immersed in pure water at 23 ° C., and 0.20% by weight. % Or less is more preferable. If the saturated water absorption exceeds 0.25% by weight, the optical disk is likely to be warped and deformed in the process of moisture absorption and dehumidification, and a focus error and a tracking error are likely to occur. The following measurement method was used for warp deformation in the process of moisture absorption and dehumidification of the optical disk. In other words, it occurs when the disk is exposed to a temperature of 30 ° C. and a humidity of 90% RH (A environment) until the saturated water absorption is reached and then moved to an environment of 23 ° C. and a humidity of 50% RH (B environment). The tilt change at the 58 mm portion from the center is measured over time, and the difference between the maximum value of the tilt change and the value when reaching the steady state (ΔTilt) is compared. At this time, ΔTilt of the disk is within 0.9 degree, preferably within 0.75 degree, and more preferably within 0.5 degree.
[0039]
The BisP-PRD resin, which is a raw material resin for an optical disk substrate provided by the present invention, is produced by a conventionally known method (solution polymerization method, melt polymerization method, etc.), and then filtered in a solution state to obtain impurities and foreign matters. Is preferably removed thoroughly. Further, in the extrusion process (pelletizing process) for obtaining a pellet-like polycarbonate resin for use in injection molding (including injection compression molding), foreign matters are removed by passing a sintered metal filter or the like in the molten state. Is preferred. As the filter, those having a filtration accuracy of 10 μm are preferably used. Moreover, it is also preferable to add additives, such as antioxidant containing a phosphorus atom, as needed. In any case, it is necessary that the raw material resin before injection molding (including injection compression molding) has a low content of foreign matters, impurities, solvents and the like as much as possible.
[0040]
When manufacturing an optical disk substrate from the BisP-PRD resin, an injection molding machine (including an injection compression molding machine) is usually used. The molding machine may be a commonly used one, but it has low adhesion between the cylinder and screw and the resin from the viewpoint of suppressing the generation of carbides and improving the reliability of the disk substrate, and also has corrosion resistance and wear resistance. It is preferable to use a material made of a material exhibiting properties. The environment of the molding process is preferably as clean as possible in view of the object of the present invention. It is also important to take into consideration that the material used for molding is sufficiently dried to remove moisture, and that no retention that causes decomposition of the molten resin occurs.
[0041]
The optical disk substrate thus formed is suitably used as a substrate for high-density optical disks represented by BD (Blu-ray Disc) and HD-DVD-RAM as well as current optical disks such as DVD (Digital Versatile Disc). The
[0042]
Since the optical disk substrate of the present invention is extremely excellent in precision transfer of BisP-PRD resin as a raw material, the interval between pit rows or groove rows is 0.1 to 0.8 μm, preferably 0.1 to 0.1. An optical disk substrate having a thickness of 5 μm, more preferably 0.1 to 0.35 μm can be easily obtained by a conventional molding method. The optical depth of the grooves or pits is λ / 8n to λ / 2n, preferably λ / 6n to λ / 2n, preferably λ / 6n to λ / 2n, with respect to the wavelength λ of the laser beam used for recording and reproduction and the refractive index n of the substrate. An optical disk substrate preferably in the range of λ / 4n to λ / 2n can be obtained. Thus, an optical disk substrate having a recording density of 100 Gbit / inch ² or more can be easily provided.
[0043]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to this unless it exceeds the meaning. In the examples or comparative examples, “parts” represents parts by weight. Measurement of physical properties of various resins and molding / evaluation of optical disk substrates using the resins were performed according to the following methods.
[0044]
(1) Glass transition temperature Using a thermal analysis system DSC-2910 manufactured by TA Instruments, under a nitrogen atmosphere (nitrogen flow rate: 40 ml / min) / temperature increase rate: 20 ° C./min. .
[0045]
(2) Storage elastic modulus Shear storage elasticity in a rubber region to a glass region under a condition of a frequency of 89.7 rad / sec and a temperature decrease rate of 2 ° C./min using a dynamic viscoelasticity measuring device RDAII manufactured by Rheometric Co. The temperature dependence of the rate was measured. The values shown in Table 1 are values obtained by reading the values at Tg′−5 ° C. from the temperature dependence curve. Here, the mechanical glass transition temperature obtained from the temperature dependence curve of the shear loss elastic modulus (G ″) measured at the same time as the “Tg ′” shear storage elastic modulus (G ′) of “Tg′−5 ° C.” Indicates.
[0046]
(3) Water absorption rate According to ASTM D-570, a φ45 mm molded plate was immersed in water, and the weight change rate (% by weight) was obtained.
[0047]
(4) Transferable Nissei Resin Kogyo injection molding machine MO40D-3H, optical disk with a diameter of 120 mm and a thickness of 0.6 mm using a stamper with grooves 200 nm deep, 0.5 μm apart, and 0.2 μm wide. A substrate was molded. The cylinder temperature was fixed at 360 ° C., and the mold temperature was set for each resin as shown in Table 1.
[0048]
The depth of the groove transferred from the stamper to the substrate was measured at five positions at a radius of 40 mm of the substrate using an atomic force microscope (Seiko Electronics Industry SPI-3700). The transferability of each resin was expressed as a transfer rate represented by the following formula. The larger this value, the better the transferability.
Transfer rate (%) = 100 × [groove depth of substrate / groove depth of stamper]
[0049]
(5) ΔTilt
An optical disk substrate having a diameter of 120 mm and a thickness of 1.2 mm was injection-molded from each pellet using an injection molding machine MO40D-3H manufactured by Nissei Plastic Industry. Next, a reflective film, a dielectric layer 1, a phase change recording film, and a dielectric layer 2 were sequentially deposited on the substrate, and a polycarbonate thin film cover layer was bonded thereon to obtain an optical disk.
[0050]
The optical disk was exposed to reach a saturated water absorption rate in an environment (temperature A) at 30 ° C. and humidity 90% RH, and then moved to an environment (temperature B) at 23 ° C. and humidity 50% RH. Thereafter, the tilt change of 58 mm from the center caused by the environmental change was measured over time by the 3D shape measuring instrument DLD-3000U manufactured by Japan EM, and the value at which the tilt change reached the maximum and the value reached the steady state. The difference between the two was ΔTilt.
[0051]
[Example 1]
A reactor equipped with a thermometer, a stirrer, and a reflux condenser was charged with 49.2 parts of a 48% aqueous sodium hydroxide solution and 357.6 parts of ion-exchanged water, and 1,1-bis (4-hydroxyphenyl) was added thereto. After 45.3 parts of propane and 0.09 part of hydrosulfite were dissolved, 202.6 parts of methylene chloride was added, and 23.6 parts of phosgene was blown in at about 15 to 25 ° C. over about 40 minutes with stirring. After completion of the phosgene blowing, 16.4 parts of a 48% aqueous sodium hydroxide solution and 1.89 parts of p-tert-butylphenol were added, stirring was resumed, and after emulsification, 0.07 parts of triethylamine was added. The reaction was terminated by stirring for a period of time. After completion of the reaction, the product is diluted with methylene chloride, washed with water, acidified with hydrochloric acid, washed with water, and further washed with water until the conductivity of the aqueous phase becomes substantially the same as that of ion-exchanged water. Obtained. Next, this solution is passed through a filter having a mesh opening of 0.3 μm, and further dropped into warm water in a kneader with an isolation chamber having a foreign matter outlet at the bearing, and the polycarbonate resin is flaked while distilling off methylene chloride. The liquid-containing flakes were pulverized and dried to obtain a powder. Thereafter, 0.0025 wt% tris (2,4-di-tert-butylphenyl) phosphite and 0.05 wt% stearic acid monoglyceride are added to the powder and mixed uniformly. The mixture was melt-kneaded while degassing with a twin-screw extruder [KTX-46 manufactured by Kobe Steel Co., Ltd.] to obtain polycarbonate resin pellets. Table 1 shows the glass transition temperature, storage elastic modulus, water absorption, and photoelastic constant of the pellet.
[0052]
From the pellet, an injection molding machine (Nissei Plastic Industries MO40D-3H), a mold having a cavity thickness of 0.6 mm, a diameter of 120 mm, and a stamper in which grooves having a depth of 200 nm, an interval of 0.5 μm, and a width of 0.2 μm are engraved The optical disk substrate was molded under the conditions of a cylinder set temperature of 360 ° C., a mold temperature of 119 ° C., a filling time of 0.2 seconds, a cooling time of 15 seconds, and a clamping force of 40 tons. The results of evaluation of transferability at this time are also shown in Table 1.
[0053]
[Comparative Example 1]
Substrate molding was performed in the same manner as in Example 1 except that a polycarbonate resin obtained from 2,2-bis (4-hydroxyphenyl) propane (Teijin Kasei Panlite AD-5503) was used and the mold temperature was 112 ° C. The transferability of the substrate was evaluated. The transferability evaluation results at this time are shown in Table 1 together with the resin properties.
[0054]
【The invention's effect】
According to the present invention, when a substrate of an optical disk, particularly a high-density optical disk, is manufactured by an injection molding method or the like, the concavo-convex shape imprinted in advance on the stamper is accurately transferred (high transfer rate) and water absorption Therefore, it is possible to provide an optical disk substrate that is less warped and deformed, and the effect it produces is exceptional.
[0055]
[Table 1]

note. ΔT = difference between glass transition temperature and mold temperature = Tg-Tmo

Claims (2)

An aromatic having a saturated water absorption of 0.25% by weight or less and 100 mol% of carbonate-bonded repeating units derived from 1,1-bis (4-hydroxyphenyl) propane represented by the following formula [1] The interval between pit rows or groove rows made of polycarbonate resin is 0.1 to 0.8 μm, and the optical depth of the pits or grooves is λ with respect to the wavelength λ of the laser beam used for recording and reproduction and the refractive index n of the substrate. An optical disk substrate in the range of / 8n to λ / 2n .

  The optical disk substrate according to claim 1, wherein a transfer rate of pits or grooves imprinted by the stamper is 95% or more.