JP3897695B2

JP3897695B2 - Write-once optical recording medium with low-to-high recording polarity for short wavelengths

Info

Publication number: JP3897695B2
Application number: JP2002381401A
Authority: JP
Inventors: 登笹
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2002-12-27
Filing date: 2002-12-27
Publication date: 2007-03-28
Anticipated expiration: 2022-12-27
Also published as: JP2004213753A

Description

【０００１】
【発明の属する技術分野】
本発明は、追記型光記録媒体（ＷＯＲＭ：ＷｒｉｔｅＯｎｃｅＲｅａｄＭａｎｙ）、特に青色レーザ波長或いはそれ以下の領域でも高密度の記録が可能な追記型光記録媒体に関する。
【０００２】
【従来の技術】
超高密度の記録が可能となる青色レーザの開発は急速に進んでおり、それに対応した追記型光記録媒体の開発が行われている。
従来の追記型光記録媒体では、有機材料からなる記録層にレーザ光を照射し、主に有機材料の分解・変質による屈折率変化を生じさせることで記録ピットを形成させており、記録層に用いられる有機材料の光学定数や分解挙動が、良好な記録ピットを形成させるための重要な要素となっている。
従って、記録層に用いる有機材料としては、青色レーザ波長に対する光学的性質や分解挙動の適切な材料を選択する必要がある。即ち、未記録時の反射率を高め、またレーザの照射によって有機材料が分解し大きな屈折率変化が生じるようにするため（これによって大きな変調度が得られる）、記録再生波長は大きな吸収帯の長波長側の裾に位置するように選択される。
何故ならば、有機材料の大きな吸収帯の長波長側の裾は、適度な吸収係数を有し且つ大きな屈折率が得られる波長領域となるためである。
しかしながら、青色レーザ波長に対する光学的性質が従来並みの値を有する有機材料は殆ど見出されていない。これは、青色レーザ波長近傍に吸収帯を持つ有機材料を得るためには、分子骨格を小さくするか又は共役系を短くする必要があるが、そうすると吸収係数の低下、即ち屈折率の低下を招くためである。
つまり、青色レーザ波長近傍に吸収帯を持つ有機材料は多数存在し、吸収係数を制御することは可能となるが、大きな屈折率を持たないため、大きな変調度を得ることができなくなる。
【０００３】
青色レーザ対応の有機材料としては、例えば、特許文献１〜５に記載がある。
しかし、これらの公報では、実施例を見ても溶液と薄膜のスペクトルを測定しているのみで、記録再生に関する記載はない。
特許文献６〜８には、実施例に記録の記載があるものの、記録波長は４８８ｎｍであり、また記録条件や記録密度に関する記載はなく、良好な記録ピットが形成できた旨の記載があるのみである。
特許文献９には、実施例に記録の記載があるものの、記録波長は４３０ｎｍであり、また記録条件や記録密度に関する記載はなく、良好な変調度が得られた旨の記載があるのみである。
特許文献１０〜１９には、実施例に記録波長４３０ｎｍ、ＮＡ０．６５での記録例があるが、最短ピットが０．４μｍという低記録密度条件（ＤＶＤと同等の記録密度）である。
特許文献２０には、記録再生波長は４０５〜４０８ｎｍであるが、記録密度に関する具体的な記載がなく、１４Ｔ−ＥＦＭ信号の記録という低記録密度条件である。
【０００４】
以上のように、現在実用化されている青色半導体レーザの発振波長の中心である４０５ｎｍ近傍においては、従来の追記型光記録媒体の記録層に要求される光学定数と同程度の光学定数を有する有機材料が殆んど存在しない。
また、４０５ｎｍ近傍で記録条件を明確にし、ＤＶＤよりも高記録密度で記録された例はない。
更に、従来の有機材料を用いた追記型光記録媒体では、記録再生波長近傍に有機材料の主吸収帯が存在するため、有機材料の光学定数の波長依存性が大きくなり（僅かな波長変動量δλに対して複素屈折率の変動量δｎやδｋが非常に大きくなる。図１参照）、レーザの個体差や環境温度の変化等による記録再生波長の変動に対し、記録感度、変調度、ジッタ、エラー率といったような記録特性や、反射率等が大きく変化するという問題があった。
一方、色素開発のコストと労力を低減させるため、色素の吸収極大が書き込み光の波長よりも長波長にある光記録媒体が、特許文献２１に記載されているが、この文献記載の発明と本発明との相違については後で説明する。
【０００５】
【特許文献１】
特開２００１−１８１５２４号公報
【特許文献２】
特開２００１−１５８８６５号公報
【特許文献３】
特開２０００−３４３８２４号公報
【特許文献４】
特開２０００−３４３８２５号公報
【特許文献５】
特開２０００−３３５１１０号公報
【特許文献６】
特開平１１−２２１９６４号公報
【特許文献７】
特開平１１−３３４２０６号公報
【特許文献８】
特開２０００−４３４２３号公報
【特許文献９】
特開平１１−５８９５５号公報
【特許文献１０】
特開２００１−３９０３４号公報
【特許文献１１】
特開２０００−１４９３２０号公報
【特許文献１２】
特開２０００−１１３５０４号公報
【特許文献１３】
特開２０００−１０８５１３号公報
【特許文献１４】
特開２０００−２２２７７２号公報
【特許文献１５】
特開２０００−２１８９４０号公報
【特許文献１６】
特開２０００−２２２７７１号公報
【特許文献１７】
特開２０００−１５８８１８号公報
【特許文献１８】
特開２０００−２８０６２１号公報
【特許文献１９】
特開２０００−２８０６２０号公報
【特許文献２０】
特開２００１−１４６０７４号公報
【特許文献２１】
特開２００２−７４７４０号公報
【０００６】
【発明が解決しようとする課題】
従来、特に追記型光記録媒体では、ハイ・ツー・ロー（ＨｉｇｈｔｏＬｏｗ）記録極性が常識である。従って、従来と同様な複素屈折率を有する色素等の有機材料を選択する必要があるが、上述したように、青色レーザ波長以下の記録再生波長領域で、赤色レーザ波長領域と同等の複素屈折率を実現することは非常に困難である。また、青色レーザ波長以下の記録再生波長領域で、赤色レーザ波長領域と同等の複素屈折率を有する有機材料が存在した場合でも、その有機材料の複素屈折率を記録再生波長に最適化することは非常に困難である。
何故ならば、一般的に短波長対応の有機材料は、分子骨格が小さいためドナーやアクセプター効果を有する置換基を導入できる部分が少なくなるし、分子骨格が大きい場合でも共役系が短いため、ドナーやアクセプター効果を有する置換基の効果が十分発揮されなくなるからである。
【０００７】
また、従来の場合、ハイ・ツー・ロー記録極性を実現させるには、例えば記録再生波長に対し、有機材料層の吸収帯を短波長側に位置するようにし、かつ記録再生波長をその吸収帯の裾に位置させなければならないが、この条件では、記録再生波長の選択によって、有機材料層をその都度設計しなければならないという問題、或いは、記録再生時のレーザの波長変動に対し、記録再生特性が大幅に変化してしまうという問題があった。
そこで、本発明は、次のイ）〜ハ）のような追記型光記録媒体の提供を目的とする。
イ）５００ｎｍ以下の記録再生波長、特に４０５ｎｍ近傍の波長領域であっても記録再生可能な生産性に優れた（生産性良く作製できる）追記型光記録媒体。
ロ）記録再生波長の変動に対し、記録感度、変調度、ジッタ、エラー率といったような記録特性や、反射率等の変化が少ない追記型光記録媒体。
ハ）溝部と溝間部の両方に記録可能な追記型光記録媒体。
【０００８】
【課題を解決するための手段】
上記課題は、次の１）〜１５）の発明によって解決される。
１）基板上に、記録再生波長に対して記録を実現させるのに十分な光吸収機能を有する有機材料層、反射層が順次設けられた構造を有し、記録極性がロー・ツー・ハイであり、波長５００ｎｍ以下の光により記録再生可能な追記型光記録媒体。
２）基板上に、反射層、記録再生波長に対して記録を実現させるのに十分な光吸収機能を有する有機材料層、カバー層が順次設けられた構造を有し、記録極性がロー・ツー・ハイであり、波長５００ｎｍ以下の光により記録再生可能な追記型光記録媒体。
３）有機材料層と反射層の間に断熱層を有する１）又は２）記載の追記型光記録媒体。
４）断熱層が、ＳｉＯ_２、ＺｎＳ・ＳｉＯ_２、ＺｒＯ_２の何れかを主成分とする材料からなる３）記載の追記型光記録媒体。
５）断熱層が、ＺｎＳ、ＺｒＯ_２、Ｙ_２Ｏ_３及びＳｉＯ_２からなる３）記載の追記型光記録媒体。
６）断熱層が、ＺｒＯ_２、ＴｉＯ_２、ＳｉＯ_２、及びＸからなり、ＸがＡｌ_２Ｏ_３、ＭｇＯ、ＣａＯ、ＮｂＯ、Ｙ_２Ｏ_３、ＣｅＯから選ばれた少なくとも１つである３）記載の追記型光記録媒体。
７）有機材料層中の有機材料は、その主吸収帯が記録再生波長に対して長波長側に位置し、かつ記録再生波長近傍には主吸収帯に帰属しない吸収帯を有する１）〜６）の何れかに記載の追記型光記録媒体。
８）基板上に、有機材料層とこれに隣接する光吸収層が設けられた構造を有し、記録極性がロー・ツー・ハイであり、波長５００ｎｍ以下の光により記録再生可能な追記型光記録媒体。
９）基板上に、光吸収層、有機材料層、反射層が順次設けられた構造を有する８）記載の追記型光記録媒体。
１０）基板上に、反射層、有機材料層、光吸収層、カバー層が順次設けられた構造を有する８）記載の追記型光記録媒体。
１１）光吸収層の光吸収機能により、有機材料層に複素屈折率変化、体積変化、空洞部の何れかを生じて記録極性がロー・ツー・ハイ化する８）〜１０）の何れかに記載の追記型光記録媒体。
１２）光吸収層の光吸収機能により、光吸収層が変形して記録極性がロー・ツー・ハイ化する８）〜１０）の何れかに記載の追記型光記録媒体。
１３）有機材料層中の有機材料の主吸収帯が記録再生波長に対して長波長側に位置する８）〜１２）の何れかに記載の追記型光記録媒体。
１４）更に有機材料層中の有機材料が、（記録再生波長における有機材料層の光吸収機能）＜（記録再生波長における光吸収層の光吸収機能）の関係を満足する１３）記載の追記型光記録媒体。
１５）基板に案内溝を有し、溝部（グルーブ）と溝間部（ランド）の両方に記録部が形成される１）〜１４）の何れかに記載の追記型光記録媒体。
【０００９】
以下、上記本発明について詳しく説明する。
従来、追記型光記録媒体には高反射率化が要求されてきた。これはＲＯＭとの互換性を重視してきたためである。
しかしながら、現在開発が行われている青色レーザ波長に対応した光記録媒体では、相変化を利用した書き換え型の光記録媒体がＲＯＭに先行して開発されており、書き換え型の光記録媒体は、青色波長領域での標準媒体となっている。
この書き換え型の光記録媒体は、一般的に反射率が１０％程度以下の低反射率である。従って、青色レーザ波長以下の短波長領域では、もはや高反射率化という課題はさほど重要でなくなる。また、青色レーザ波長以下の短波長領域では、反射層自体の反射率も低下するため、ＲＯＭが実現された場合でも、必ずしも従来のような高い反射率を有することは期待できない。
そこで本発明では、青色レーザ波長以下（５００ｎｍ以下）の記録再生波長において、追記型光記録媒体の記録極性をロー・ツー・ハイ（ＬｏｗｔｏＨｉｇｈ）化することを提案する。
【００１０】
なお、前述の特許文献２１に記載の技術では、従来の色素（有機化合物）と記録再生波長の関係を逆転させた追記型光記録媒体を実現させているが、この技術は色素の主吸収帯の短波長側の裾に記録再生波長を合わせたものであって、色素の記録再生波長への整合が容易になった訳ではない（図２参照）。また、この技術においては、記録極性に関する記載がなく、本発明とは技術思想が異なる。
本発明の第一の態様では、記録再生波長を主吸収帯に合わせるのではなく、主吸収帯に帰属せず主吸収帯よりも短波長側にある吸収帯近傍に記録再生波長を設定する（図３参照。図中の斜線領域に記録再生波長を設定する）。
言い換えれば、記録再生波長近傍に、主吸収帯に帰属しない吸収帯（主吸収帯よりも吸収機能が小さく、スペクトルがブロードな吸収帯）を有し、この吸収帯よりも長波長側に主吸収帯を有する有機化合物を用いる（図３参照）。
【００１１】
なお、本発明でいう「主吸収帯」とは、図４に示すように、可視域の範囲で最も吸収の大きな吸収帯を指し、一般的にはＨＯＭＯ−ＬＵＭＯ（ホモ−ルモ）の遷移に基づく吸収帯を指す。
従って、例えば、図５に示すような吸収スペクトルを有する色素（有機材料）では、３００ｎｍ以下の波長域に最も大きな吸収帯を有するが、本発明ではこの吸収帯を主吸収帯とは呼ばず、７００ｎｍ近傍の吸収帯（可視域で最も大きな吸収帯）を主吸収帯と呼ぶ。
また、本発明でいう「主吸収帯に帰属せず、主吸収帯よりも短波長側にある吸収帯」とは、図４に示すように、主吸収帯とは別の遷移に基づく吸収帯を指す（ＨＯＭＯ−ＬＵＭＯの遷移に基づく吸収帯ではない）。
【００１２】
本発明では記録極性をロー・ツー・ハイ化するが、そのメリットとしては次のイ）〜ニ）などが挙げられる。
イ）有機材料の主吸収帯と記録再生波長の位置関係を細かく制御する必要がないため、ＣＤ−ＲやＤＶＤ−Ｒ等で検討されてきた一般的な色素、或いは合成の容易な化合物を利用することが可能である。
ロ）従来の追記型光記録媒体と同じか又は断熱層を追加しただけの層構成であり、光記録媒体の構成が単純である。
ハ）有機材料の主吸収帯近傍に記録再生波長を設定しないため、短波長化が容易である（記録再生波長の選択の自由度が大きい）
ニ）記録再生波長の変動に対し、記録感度、変調度、ジッタ、エラー率といったような記録特性や、反射率等の変化を小さくすることができる（大きな吸収係数を有する主吸収帯の吸収機能を利用しないため、記録再生波長近傍での有機材料の複素屈折率変動が少ないことによる）
【００１３】
本発明の第一の態様では、記録極性をロー・ツー・ハイ化するため、基板上に、記録再生波長に対して記録を実現させるのに十分な光吸収機能を有する有機材料層、反射層が順次設けられた光記録媒体構成、或いは、基板上に、反射層、記録再生波長に対して記録を実現させるのに十分な光吸収機能を有する有機材料層、カバー層が順次設けられた光記録媒体構成を採用する。
この光記録媒体構成では、有機材料層以外の層は記録を実現させるだけの光吸収機能を持たないため、有機材料層が主たる光吸収機能を担う必要がある。
本発明で用いることのできる有機化合物としては、記録再生波長に対して記録を実現させるのに十分な光吸収機能を有するものであれば何ら制限はないが、ロー・ツー・ハイ記録を容易に実現させるため、主吸収帯が記録再生波長に対して長波長側に位置し、記録再生波長近傍には主吸収帯に帰属しない吸収帯を有する有機材料を用いることが好ましい。
【００１４】
なお、この記録再生波長近傍に存在する、主吸収帯に帰属しない吸収帯は、記録を実現させるのに十分な光吸収機能を有する必要がある。
例えば、図５の吸収スペクトルを有する色素（有機材料）では、主吸収帯に帰属しない吸収帯が、記録を実現させるのに十分な光吸収能を持っているが、図８の吸収スペクトルを有する色素（有機材料）では、主吸収帯に帰属しない吸収帯が記録再生波長域とずれており、記録を実現させるのに十分な光吸収能を持っていない（図５、図８中の破線領域は、現在実用化されている青色レーザ波長４０５ｎｍを中心に、その変動可能性範囲を含めた記録再生波長範囲を示したものである）。
従って、基板上に、記録再生波長に対して記録を実現させるのに十分な光吸収機能を有する有機材料層、反射層が順次設けられた光記録媒体構成、或いは、基板上に、反射層、記録再生波長に対して記録を実現させるのに十分な光吸収機能を有する有機材料層、カバー層が順次設けられた光記録媒体構成を採用する場合は、有機材料層として、例えば図５のような吸収スペクトルを有する有機材料を用いることが好ましい。
【００１５】
有機材料層として、主吸収帯が記録再生波長に対して長波長側に位置し、記録再生波長近傍には主吸収帯に帰属しない吸収帯を有する有機材料を用いることで、容易に記録極性のロー・ツー・ハイ化が実現でき、また有機材料層が主たる光吸収機能を担うため、光記録媒体構成の単純化を図ることができる。
以上説明した本発明の第一の態様においては、有機材料層の光吸収機能によって、次のイ）〜ニ）の記録原理により記録部を形成する。
イ）基板を変形させる。
ロ）有機材料層の複素屈折率を変化させる。
ハ）有機材料層の体積を変化させる。
ニ）有機材料層に空洞部を形成させる。
しかし、本発明には、上記第一の態様だけでなく「主吸収帯が記録再生波長に対して長波長側に位置し、記録再生波長近傍には主吸収帯に帰属しない吸収帯を有する有機材料」を必ずしも使用しなくてよい第二の態様も包含される。
【００１６】
本発明の第二の態様では、記録極性をロー・ツー・ハイ化するため、基板上に、光吸収層と有機材料層が隣接する構造を有する光記録媒体構成を採用する。
この光記録媒体構成では、光吸収層に主たる光吸収機能を担わせることができ、有機材料層から主たる光吸収機能を除くことが可能となるため、有機材料の選択の自由度を大幅に高めることができる。
この光記録媒体構成では、有機材料として、前述したような、「主吸収帯が記録再生波長に対して長波長側に位置し、記録再生波長近傍には主吸収帯に帰属しない吸収帯を有する有機材料」が選択できるだけでなく、任意の有機材料を用いることができる。即ち、記録再生波長と有機材料層の吸収帯の位置関係や、記録再生波長域での有機材料層の吸収機能等に大きな制限はない。
例えば、記録再生波長域で殆ど吸収を持たない図８に示すような吸収スペクトルを示す有機材料を用いることも可能である。
但し、未記録時の反射率を高め、また記録再生特性の向上を図るためには、（記録再生波長における有機材料層の光吸収機能）＜（記録再生波長における光吸収層の光吸収機能）の関係を満足することが好ましい。
【００１７】
この光記録媒体構成では、従来の有機材料を用いた追記型光記録媒体に対して光吸収層を追加したため、従来には無かった光吸収層の変形等の記録原理を利用することができ、記録極性のロー・ツー・ハイ化がより容易に実現できる。
基板上に、光吸収層と有機材料層が隣接する構造を有する光記録媒体構成の具体例としては、基板上に、光吸収層、有機材料層、反射層が順次設けられた構造を有する光記録媒体、或いは、基板上に、反射層、有機材料層、光吸収層、カバー層が順次設けられた構造を有する光記録媒体等が挙げられる。
以上説明した本発明の第二の態様においては、光吸収層の光吸収機能によって、次のイ）〜ホ）の記録原理により記録部を形成する。
イ）光吸収層を変形させる。
ロ）基板を変形させる。
ハ）有機材料層の複素屈折率を変化させる。
ニ）有機材料層の体積を変化させる。
ホ）有機材料層に空洞部を形成させる。
但し、上記の条件を満足しても、必ずしも記録極性をロー・ツー・ハイ化できる訳ではなく、各層の膜厚や複素屈折率を適宜最適化する必要があることは言うまでもない。
【００１８】
また、本発明では、
イ）記録再生波長に対して主吸収帯が長波長側に存在する有機材料を選択するか、或いは、主吸収帯が記録再生波長に対して長波長側に位置し、記録再生波長近傍には主吸収帯に帰属しない吸収帯を有する有機材料を選択する、
ロ）有機材料層に隣接して光吸収層を設ける、
ことにより、従来のように、有機材料の吸収スペクトルと記録再生波長の関係を保つ必要がなくなり、記録再生波長の変動に対し、記録感度、変調度、ジッタ、エラー率といったような記録特性や、反射率等の変化を従来に比べて大幅に低減できる（図３参照。従来の追記型光記録媒体の吸収スペクトルと記録再生波長の関係を図１〜図２に示す。本発明の追記型光記録媒体では、記録再生波長近傍での複素屈折率の変化が非常に緩やかになる）。
【００１９】
更に本発明の第一の態様では、有機材料層の複素屈率変化や体積変化を効率よく発生させ、また記録感度を向上させるため、有機材料層と反射層の間に断熱層を設けることも好ましい。この断熱層は、いわゆる断熱効果を担うだけでなく、未記録時の反射率を制御したり、変調度を制御するためにも利用可能である。
従来の有機材料層を用いた追記型光記録媒体では、一般的にスピンコート法によって有機材料層が形成されるため、有機材料層の膜厚が（溝部の膜厚）＞（溝間部の膜厚）となってしまう。また、有機材料のみが光吸収機能を担い、有機材料が光学定数変化等を起こして主たる変調度を発生させていた。
従って、溝部では良好な記録が行えても、溝間部では有機材料層膜厚が薄くなるため、光吸収機能の低下と、記録による位相差変化量の低下を招き、一般的には良好な記録が行えない（特に基板上に有機材料層、反射層が順次積層された光記録媒体の溝間部では、反射層の高熱伝導性によって、有機材料層内の温度が記録部を形成させるだけの温度に達し難い）。
【００２０】
但し、有機材料層を蒸着法や、塗布条件を最適化したスピンコート法の適用により、溝間部でも溝部と同様な記録再生特性を得ることは可能である。
一方、本発明の第一の態様では、有機材料と反射層の間に断熱層を導入するため、溝間部で有機材料層膜厚が薄くなって十分な光吸収機能を確保できなくても、断熱層によって反射層からの熱の拡散を抑制でき、有機材料層を記録部が形成できるまでの温度に高めることができる。その結果、記録部を溝部と溝間部の何れか一方だけでなく、両方に形成することができる。
なお、溝部と溝間部で、記録感度や変調度等の記録再生特性は異ってもよい（必ずしも同一である必要はない）。
【００２１】
また、本発明の第二の態様では、従来光吸収機能を担っていた有機材料層から、主たる光吸収機能を除き、有機材料層に隣接して光吸収層を設ける。
この光記録媒体の光吸収層は、後述するようにセラミックス、金属、半金属等の材料から構成され、通常はスパッタ法や蒸着法によって成膜されるため、溝部と溝間部での光吸収機能に差が生じない。
従って、例えばスピンコート法によって成膜された有機材料層が光吸収層上に設けられた光記録媒体では、溝部と溝間部の有機材料層の膜厚の違いによって、変調度等の差異を生じる場合はあるが、容易に溝間部と溝部に記録部を形成させることが可能となる。そのため容易に高密度化できる。
但し、前述のように、本発明では溝部と溝間部の一方にのみ記録部を形成させてもよい。
【００２２】
本発明の光記録媒体は、基本的には基板又は基板とカバー層、有機材料層、断熱層、反射層、或いは基板又は基板とカバー層、有機材料層、光吸収層、反射層から構成されるものであるが、更に必要に応じて下引層、上引層、保護層等を設けても良い。
基板の材質としては、基本的には記録光及び再生光に対し透明であればよい。
このような材料としては、例えばアクリル樹脂、メタクリル樹脂、ポリカーボネート樹脂、ポリオレフィン樹脂（特に非晶質ポリオレフィン）、ポリエステル樹脂、ポリスチレン樹脂、エポキシ樹脂等の樹脂、ガラス、ガラス上に光硬化性樹脂等の放射線硬化性樹脂からなる樹脂層を設けたもの等を使用することができる。これらの中で、高生産性、コスト、耐吸湿性などの点からは、射出成型ポリカーボネートが好ましく、耐薬品性、耐吸湿性などの点からは、非晶質ポリオレフィンが好ましい。また、高速応答、或いは空隙が発生しないなどの点からは、ガラス基板が好ましい。
有機材料層や光吸収層に接して樹脂基板又は樹脂層を設け、その樹脂基板又は樹脂層上に記録再生光の案内溝やピットを有していてもよい。
【００２３】
有機材料層に用いる有機材料としては色素が好ましい例として挙げられる。
色素としては含金属アゾ系色素、フタロシアニン系色素、ナフタロシアニン系色素、シアニン系色素、アゾ系色素、スクアリリウム系色素、含金属インドアニリン系色素、トリアリールメタン系色素、メロシアニン系色素、アズレニウム系色素、ナフトキノン系色素、アントラキノン系色素、インドフェノール系色素、キサンテン系色素、オキサジン系色素、ピリリウム系色素等が挙げられる。
また、有機材料層は、有機材料の安定や耐光性向上のために、一重項酸素クエンチャーとして遷移金属キレート化合物（例えば、アセチルアセトナートキレート、ビスフェニルジチオール、サリチルアルデヒドオキシム、ビスジチオ−α−ジケトン等）等や、記録感度向上のために金属系化合物等の記録感度向上剤を含有していても良い。
ここで金属系化合物とは、遷移金属等の金属が原子、イオン、クラスター等の形で化合物に含まれるものを言い、例えばエチレンジアミン系錯体、アゾメチン系錯体、フェニルヒドロキシアミン系錯体、フェナントロリン系錯体、ジヒドロキシアゾベンゼン系錯体、ジオキシム系錯体、ニトロソアミノフェノール系錯体、ピリジルトリアジン系錯体、アセチルアセトナート系錯体、メタロセン系錯体、ポルフィリン系錯体のような有機金属化合物が挙げられる。金属原子としては特に限定されないが、遷移金属であることが好ましい。
また、必要に応じて他系統の色素を併用することもできる。
【００２４】
更に、必要に応じて、バインダー、レベリング剤、消泡剤等を併用することもできる。
好ましいバインダーとしては、ポリビニルアルコール、ポリビニルピロリドン、ニトロセルロース、酢酸セルロース、ケトン系樹脂、アクリル系樹脂、ポリスチレン系樹脂、ウレタン系樹脂、ポリビニルブチラール、ポリカーボネート、ポリオレフィン等が挙げられる。
有機材料層の膜厚は、記録方法などにより適切な膜厚が異なる為、特に限定するものではないが、通常５０〜３００ｎｍである。
有機材料層の成膜方法としては、真空蒸着法、スパッタリング法、ドクターブレード法、キャスト法、スピンコート法、浸漬法等一般に行われている薄膜形成法が挙げられる。量産性、コスト面からはスピンコート法が好ましく、また、厚みの均一な記録層が得られるという点からは、塗布法よりも真空蒸着法等の方が好ましい。
【００２５】
スピンコート法による成膜の場合、回転数は５００〜１５０００ｒｐｍが好ましく、スピンコートの後、場合によっては加熱或いは溶媒蒸気に当てる等の処理を行っても良い。
ドクターブレード法、キャスト法、スピンコート法、浸漬法等の塗布方法により記録層を形成する場合の塗布溶媒としては、基板を侵さない溶媒であればよく、特に限定されない。
例えば、ジアセトンアルコール、３−ヒドロキシ−３−メチル−２−ブタノン等のケトンアルコール系溶媒；メチルセロソルブ、エチルセロソルブ等のセロソルブ系溶媒；ｎ−ヘキサン、ｎ−オクタン等の鎖状炭化水素系溶媒；シクロヘキサン、メチルシクロヘキサン、エチルシクロヘキサン、ジメチルシクロヘキサン、ｎ−ブチルシクロヘキサン、ｔｅｒｔ−ブチルシクロヘキサン、シクロオクタン等の環状炭化水素系溶媒；テトラフルオロプロパノール、オクタフルオロペンタノール、ヘキサフルオロブタノール等のパーフルオロアルキルアルコール系溶媒；乳酸メチル、乳酸エチル、イソ酪酸メチル等のヒドロキシカルボン酸エステル系溶媒等が挙げられる。
この他、有機材料層としては、高分子材料、相変化材料、フォトクロミック材料、サーモクロミック材料等も好ましく用いることができる。
【００２６】
光吸収層としては、十分な記録感度を確保するという点で、記録再生波長に対する吸収係数がある程度大きいものを用いることが好ましく、ＳｉＣ、Ｂ_４Ｃ、ＴｉＣ、ＷＣなどの炭化物系の非酸化物；アモルファス炭素、黒鉛、ダイアモンド等の炭素系の非酸化物、フェライト等に代表されるセラミックス；Ｔｅ−ＴｅＯ_２、Ｔｅ−ＴｅＯ_２−Ｐｄ、Ｓｂ_２Ｓｅ_３／Ｂｉ_２Ｔｅ_３、Ｇｅ−Ｔｅ−Ｓｂ−Ｓ、Ｔｅ−ＴｅＯ_２−Ｇｅ−Ｓｎ、Ｔｅ−Ｇｅ−Ｓｎ−Ａｕ、Ｇｅ−Ｔｅ−Ｓｎ、Ｓｎ−Ｓｅ−Ｔｅ、Ｓｂ−Ｓｅ−Ｔｅ、Ｓｂ−Ｓｅ、Ｇａ−Ｓｅ−Ｔｅ、Ｇａ−Ｓｅ−Ｔｅ−Ｇｅ、Ｉｎ−Ｓｅ、Ｉｎ−Ｓｅ−Ｔｌ−Ｃｏ、Ｇｅ−Ｓｂ−Ｔｅ、Ｉｎ−Ｓｅ−Ｔｅ、Ａｇ−Ｉｎ−Ｓｂ−Ｔｅ、Ａｇ−Ｚｎ、Ｃｕ−Ａｌ−Ｎｉ、Ｉｎ−Ｓｂ、Ｉｎ−Ｓｂ−Ｓｅ、Ｉｎ−Ｓｂ−Ｔｅ等の相変化記録材料；ニッケル、クロム、チタン、タンタル等の純粋金属；銅／アルミニウム、ニッケル／鉄などの合金；シリコン等の半金属；Ｇｅ等の半導体等を用いることが可能である。
そのうち、光吸収層として、Ｓｉ、Ｇｅを含有する材料を用いることが好ましく、例えば、Ｓｉ、Ｇｅ、ＳｉＣ等が好ましい例として挙げられる。
光吸収層の膜厚は、通常５〜１５０ｎｍである。
【００２７】
断熱層としては、例えば、Ａｌ_２Ｏ_３、ＭｇＯ、ＢｅＯ、ＺｒＯ_２、ＵＯ_２、ＴｈＯ_２などの単純酸化物系の酸化物；ＳｉＯ_２、２ＭｇＯ・ＳｉＯ_２、ＭｇＯ・ＳｉＯ_２、ＣａＯ・ＳｉＯ_３、ＺｒＯ_２・ＳｉＯ_２、３Ａｌ_２Ｏ_３・２ＳｉＯ_２、２ＭｇＯ・２Ａｌ_２Ｏ_３・５ＳｉＯ_２、Ｌｉ_２Ｏ・Ａｌ_２Ｏ_３・４ＳｉＯ_２などのケイ酸塩系の酸化物；Ａｌ_２ＴｉＯ_５、ＭｇＡｌ_２Ｏ_４、Ｃａ_１０（ＰＯ_４）_６（ＯＨ）_２、ＢａＴｉＯ_３、ＬｉＮｂＯ_３、ＰＺＴ＝Ｐｂ（Ｚｒ，Ｔｉ）Ｏ_３、ＰＬＺＴ＝（Ｐｂ，Ｌａ）（Ｚｒ，Ｔｉ）Ｏ_３、フェライトなどの複酸化物系の酸化物；Ｓｉ_３Ｎ_４、Ｓｉ_６−ＺＡｌ_ＺＯ_ＺＮ_８−Ｚ、ＡｌＮ、ＢＮ、ＴｉＮなどの窒化物系の非酸化物；ＳｉＣ、Ｂ_４Ｃ、ＴｉＣ、ＷＣなどの炭化物系の非酸化物；ＬａＢ_６、ＴｉＢ_２、ＺｒＢ_２などのホウ化物系の非酸化物；ＣｄＳ、ＭｏＳ_２などの硫化物系の非酸化物；ＭｏＳｉ_２などのケイ化物系の非酸化物；アモルファス炭素、黒鉛、ダイアモンド等の炭素系の非酸化物を用いることができる。
記録再生光に対する透明性や生産性の観点からは、ＳｉＯ_２を主体（主成分）とすること、或いはＺｎＳ・ＳｉＯ_２を主体（主成分）とすることが好ましい例として挙げられる。また、断熱効果を十分得るためには、ＺｒＯ_２を主体（主成分）とすることも好ましい。ここで、主成分とは、断熱層材料全体の５０重量％以上を占めることを意味する。
更に、ＺｎＳ、ＺｒＯ_２、Ｙ_２Ｏ_３、ＳｉＯ_２からなる酸化物又はＺｒＯ_２、ＴｉＯ_２、ＳｉＯ_２、及びＸからなり、ＸがＡｌ_２Ｏ_３、ＭｇＯ、ＣａＯ、ＮｂＯ、或いはＹ_２Ｏ_３、ＣｅＯなどの希土類酸化物から選ばれた少なくとも１つである材料も好ましい。
断熱層の厚みは、通常５〜２００ｎｍ程度とする。
【００２８】
有機材料層の上には、直接又は断熱層や上引層等を介して、反射層を形成してもよく、その好ましい膜厚は、５０〜３００ｎｍである。
反射層の材料としては、再生光の波長で反射率の十分高いもの、例えば、Ａｕ、Ａｌ、Ａｇ、Ｃｕ、Ｔｉ、Ｃｒ、Ｎｉ、Ｐｔ、Ｔａ、Ｃｒ、Ｐｄなどの金属を単独で或いは合金にして用いることができる。中でもＡｕ、Ａｌ、Ａｇは反射率が高く反射層の材料として適している。
また、上記金属を主成分として他の元素を含んでいても良く、他の元素としては、Ｍｇ、Ｓｅ、Ｈｆ、Ｖ、Ｎｂ、Ｒｕ、Ｗ、Ｍｎ、Ｒｅ、Ｆｅ、Ｃｏ、Ｒｈ、Ｉｒ、Ｃｕ、Ｚｎ、Ｃｄ、Ｇａ、Ｉｎ、Ｓｉ、Ｇｅ、Ｔｅ、Ｐｂ、Ｐｏ、Ｓｎ、Ｂｉなどの金属及び半金属を挙げることができる。
中でもＡｇを主成分とするものは、コストが安く高反射率が出易い点から特に好ましい。
金属以外の材料で低屈折率薄膜と高屈折率薄膜を交互に積み重ねて多層膜を形成し、反射層として用いることも可能である。
反射層を形成する方法としては、例えば、スパッタ法、イオンプレーティング法、化学蒸着法、真空蒸着法等が挙げられる。
また、基板の上や反射層の下に反射率の向上、記録特性の改善、密着性の向上等のために公知の無機系又は有機系の上引層、下引層、或いは接着層を設けることもできる。
【００２９】
反射層の上に形成する保護層の材料としては、反射層を外力から保護するものであれば特に限定されない。有機材料としては、熱可塑性樹脂、熱硬化性樹脂、電子線硬化性樹脂、ＵＶ硬化性樹脂等を挙げることができる。また、無機材料としては、ＳｉＯ_２、ＳｉＮ_４、ＭｇＦ_２、ＳｎＯ_２等が挙げられる。
熱可塑性樹脂、熱硬化性樹脂は適当な溶剤に溶解した塗布液を塗布し乾燥することによって形成することができる。
ＵＶ硬化性樹脂は、そのまま又は適当な溶剤に溶解した塗布液を塗布し、ＵＶ光を照射して硬化させることによって形成することができる。ＵＶ硬化性樹脂としては、例えば、ウレタンアクリレート、エポキシアクリレート、ポリエステルアクリレートなどのアクリレート系樹脂を用いることができる。
これらの材料は単独で用いても混合して用いても良いし、１層だけでなく多層膜にして用いても良い。
保護層の形成方法としては、記録層と同様にスピンコート法やキャスト法等の塗布法、スパッタ法、化学蒸着法等が用いられるが、中でもスピンコート法が好ましい。
保護層の膜厚は、一般に０．１〜１００μｍの範囲であるが、本発明においては、３〜３０μｍが好ましい。
また、反射層面に更に基板を貼り合わせてもよく、また反射層面相互を内面とし対向させ光学記録媒体２枚を貼り合わせても良い。
基板鏡面側に、表面保護やゴミ等の付着防止のために紫外線硬化樹脂層や、無機系薄膜等を成膜してもよい。
【００３０】
カバー層は、高密度化を図るため高ＮＡのレンズを用いる場合に必要となる。
例えば高ＮＡ化すると、再生光が透過する部分の厚さを薄くする必要がある。これは、高ＮＡ化に伴い、光学ピックアップの光軸に対してディスク面が垂直からズレる角度（いわゆるチルト角、光源の波長の逆数と対物レンズの開口数の積の２乗に比例する）により発生する収差の許容量が小さくなるためであり、このチルト角が基板の厚さによる収差の影響を受け易いためである。
従って、基板の厚さを薄くしてチルト角に対する収差の影響をなるべく小さくするようにしている。
そこで、例えば基板上に凹凸を形成して記録層とし、その上に反射層を設け、更にその上に光を透過する薄膜である光透過性のカバー層を設けるようにし、カバー層側から再生光を照射して記録層の情報を再生するような光記録媒体や、基板上に反射層を設け、その上に記録層を設け、更にこの上に光透過性を有するカバー層を設けるようにし、カバー層側から再生光を照射して記録層の情報を再生するような光記録媒体が提案されている。
【００３１】
このようにすれば、カバー層を薄型化していくことで対物レンズの高ＮＡ化に対応可能である。つまり、薄いカバー層を設け、このカバー層側から記録再生することで、更なる高記録密度化を図ることができる。
なお、このようなカバー層は、ポリカーボネートシートや、紫外線硬化型樹脂により形成されるのが一般的である。また、本発明で言うカバー層には、カバー層を接着するための層を含めてもよい。
カバー層の厚みは、通常０．０１〜０．５ｍｍ程度とする。
本発明の光記録媒体に使用されるレーザ光は、高密度記録のため波長は短いほど好ましいが、特に３５０〜５３０ｎｍのレーザ光が好ましく、その代表例としては、中心波長４０５ｎｍのレーザ光が挙げられる。
【００３２】
【実施例】
以下、本発明を実施例により更に具体的に説明するが、本発明はこれらの実施例によって限定されるものではない。
【００３３】
実施例１
溝深さ５５ｎｍのトラッキング用案内溝を有する基板上に、下記〔化１〕で示される色素からなる有機材料層（平均厚さ約６０ｎｍ）、Ａｇ反射層（厚さ１５０ｎｍ）、紫外線硬化型樹脂からなる保護層（厚さ５μｍ）を順次積層した追記型光記録媒体を作製した。
〔化１〕で示される色素の吸収スペクトルは、図５のようであり、ＣＤ−Ｒに適した吸収スペクトルを有する。
また、この〔化１〕の色素は、本発明で言うところの、「記録再生波長に対して光吸収機能を有する有機材料」であり、更に、「主吸収帯が記録再生波長に対して長波長側に位置し、記録再生波長近傍には主吸収帯に帰属しない吸収帯を有する有機材料」である。
【化１】

【００３４】
この光記録媒体に対して、パルステック工業（株）製の光ディスク評価装置ＤＤＵ−１０００（波長：４０５ｎｍ、ＮＡ：０．６５）を用いて、溝部（グルーブ部）に下記の条件で記録を行った結果、記録極性をロー・ツー・ハイ化することができた。

この光記録媒体では、記録パワー７．５ｍＷ近傍において最良ジッタが得られ、ジッタ（σ／Ｔｗ）は９．５％が得られた。
また、この時のイコライズ後の再生信号のアイパターンを図６に示すが、非常に良好な記録が実現できることが確認できた。
更に、図７に、記録パワーを変えて記録した時の、ジッタ変化、及び未記録部（△）と記録部（■）の再生信号レベル変化（反射率変化）の測定結果を示す。図７から分るように、記録コントラストも十分大きく、また良好なジッタ特性が得られた。
【００３５】
実施例２
断熱層の導入により、最良ジッタが得られる記録パワーが低下し、しかも良好なジッタが得られることを確認するため、色素層（有機材料層）と反射層の間に、表１で示される断熱層を挿入した点以外は、実施例１と同様にして追記型光記録媒体を作製した。
この光記録媒体に対して、実施例１と同様にして溝部（グルーブ部）に記録を行い、最適記録パワーと最良ジッタを測定した。結果を表１に示す。
なお、記録極性は、何れもロー・ツー・ハイであることを確認した。
更に、断熱層を導入しない実施例１の光記録媒体の場合、溝間部（ランド部）には、１１．０ｍＷ以下の記録パワー範囲でジッタを測定できるレベルの記録が行えなかったが、断熱層を導入した本実施例の光記録媒体では、溝間部でもジッタを測定可能な記録が行えることが確認できた。
但し、本実施例では、溝部と溝間部の溝形状や、色素の塗布状態の制御、或いは色素層の膜厚を最適化していないため、溝間部への記録では、溝部への記録に比べて最適記録パワーが平均で約２．０ｍＷ程度上昇し、最良ジッタも１２．０％程度となった。
【表１】

【００３６】
実施例３
溝深さ５５ｎｍのトラッキング用案内溝を有する基板上に、ＳｉＣからなる光吸収層（厚さ１０ｎｍ）、〔化２〕で示される色素からなる有機材料層（平均厚さ約６０ｎｍ）、Ａｇ反射層（厚さ１５０ｎｍ）、紫外線硬化型樹脂からなる保護層（厚さ５μｍ）を順次積層した追記型光記録媒体を作製した。
〔化２〕で示される色素の吸収スペクトルは、図８のようであり、ＣＤ−Ｒに適した吸収スペクトルを有する。
また、この〔化２〕の色素は、記録再生波長域に殆ど吸収を持たず、本発明で言うところの、「（記録再生波長における有機材料層の光吸収機能）＜（記録再生波長における光吸収層の光吸収機能）の関係を満足する有機材料」である。
【化２】

この光記録媒体に対して、パルステック工業（株）製の光ディスク評価装置ＤＤＵ−１０００（波長：４０５ｎｍ、ＮＡ：０．６５）を用いて、溝間部（ランド部）に下記の条件で記録を行った。
その結果、記録極性はロー・ツー・ハイであり、記録パワー８．５ｍＷ近傍において最良ジッタが得られ、ジッタ（σ／Ｔｗ）は１０．０％であった。
またこの時のイコライズ後の再生信号のアイパターンは図６とほぼ同様であり、非常に良好な記録を実現できることが確認できた。
更に、記録パワーを変えて記録した時の、ジッタ変化の測定結果は、図９に示す通りであり、良好なジッタ特性が得られることを確認できた。

【００３７】
以上の実施例から明らかなように、〔化１〕や〔化２〕に示すような、赤色レーザ波長に対応した色素を用いても、青色領域で良好な記録再生特性を実現できる。
また、〔化１〕や〔化２〕の色素の吸収スペクトル（図５、図８）から分るように、青色レーザ波長領域での吸収係数の変化が緩やかであるため、複素屈折率（ｎ、ｋ）の波長依存性も従来に比べて非常に小さい。
【００３８】
【発明の効果】
本発明によれば、５００ｎｍ以下の記録再生波長、特に４０５ｎｍ近傍の波長領域であっても記録再生可能で生産性に優れ、記録再生波長の変動に対し、記録感度、変調度、ジッタ、エラー率といったような記録特性や、反射率等の変化が少なく、溝部と溝間部の両方に記録可能な追記型光記録媒体を提供できる。
【図面の簡単な説明】
【図１】従来の有機材料を用いた追記型光記録媒体では、僅かな波長変動量δλに対して複素屈折率の変動量δｎやδｋが非常に大きくなることを示す図。
【図２】特許文献２１に記載の技術では、従来と同様、色素の記録再生波長への整合が容易になった訳ではないことを示す図。
【図３】本発明は、記録再生波長を主吸収帯に合わせるものではなく、主吸収帯に帰属せず、主吸収帯よりも短波長側にある吸収帯近傍（図中の斜線領域）に記録再生波長を設定することを示す図。
【図４】本発明でいう「主吸収帯」を説明するための図。
【図５】実施例１で用いた色素の吸収スペクトルを示す図。
【図６】実施例１の追記型光記録媒体の再生信号のアイパターンを示す図。
【図７】実施例１で、記録パワーを変えて記録した時の、ジッタ変化、及び未記録部（△）と記録部（■）の変化の測定結果を示す図。
【図８】実施例３で用いた色素の吸収スペクトルを示す図。
【図９】実施例３で、記録パワーを変えて記録した時の、ジッタ変化の測定結果を示す図。
【符号の説明】
ｎ複素屈折率の実部
ｋ複素屈折率の虚部
δλ 波長変動量
δｎ複素屈折率の変動量
δｋ複素屈折率の変動量[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a write-once optical recording medium (WORM), and more particularly to a write-once optical recording medium capable of high-density recording even in a blue laser wavelength region or less.
[0002]
[Prior art]
Development of blue lasers capable of ultra-high density recording is rapidly progressing, and write-once type optical recording media corresponding thereto are being developed.
In conventional write-once optical recording media, recording pits are formed by irradiating a recording layer made of an organic material with laser light and causing a change in refractive index mainly due to decomposition and alteration of the organic material. The optical constant and decomposition behavior of the organic material used are important factors for forming good recording pits.
Accordingly, it is necessary to select an organic material used for the recording layer that is suitable for optical properties and decomposition behavior with respect to the blue laser wavelength. In other words, the recording / reproducing wavelength has a large absorption band in order to increase the reflectivity when unrecorded, and to cause a large change in refractive index due to decomposition of the organic material by laser irradiation (this provides a large degree of modulation). It is selected so as to be located at the bottom of the long wavelength side.
This is because the skirt on the long wavelength side of the large absorption band of the organic material is a wavelength region having an appropriate absorption coefficient and a large refractive index.
However, few organic materials have been found in which the optical properties with respect to the blue laser wavelength have the same values as before. In order to obtain an organic material having an absorption band in the vicinity of the blue laser wavelength, it is necessary to reduce the molecular skeleton or shorten the conjugated system, but this leads to a decrease in absorption coefficient, that is, a decrease in refractive index. Because.
That is, there are many organic materials having an absorption band near the blue laser wavelength, and the absorption coefficient can be controlled. However, since there is no large refractive index, a large degree of modulation cannot be obtained.
[0003]
For example, Patent Documents 1 to 5 describe organic materials for blue lasers.
However, these publications only measure the spectra of the solution and the thin film even when looking at the examples, and there is no description regarding recording and reproduction.
In Patent Documents 6 to 8, although there is a description of recording in the examples, the recording wavelength is 488 nm, and there is no description regarding recording conditions and recording density, and only a description that good recording pits can be formed. It is.
Although Patent Document 9 has a description of recording in the examples, the recording wavelength is 430 nm, and there is no description regarding recording conditions and recording density, but only a description that a good degree of modulation has been obtained. .
In Patent Documents 10 to 19, there is an example of recording at a recording wavelength of 430 nm and NA of 0.65 in the examples, but the low recording density condition (recording density equivalent to DVD) is that the shortest pit is 0.4 μm.
In Patent Document 20, the recording / reproducing wavelength is 405 to 408 nm, but there is no specific description regarding the recording density, and a low recording density condition of recording a 14T-EFM signal.
[0004]
As described above, in the vicinity of 405 nm, which is the center of the oscillation wavelength of the blue semiconductor laser currently in practical use, it has an optical constant comparable to that required for the recording layer of the conventional write-once optical recording medium. There is almost no organic material.
In addition, there are no examples in which recording conditions are clarified near 405 nm and recording is performed at a higher recording density than DVD.
Furthermore, in a write-once type optical recording medium using a conventional organic material, the main absorption band of the organic material exists in the vicinity of the recording / reproducing wavelength, so the wavelength dependency of the optical constant of the organic material increases (slight wavelength fluctuation amount). The complex refractive index fluctuations δn and δk are very large with respect to δλ (see Fig. 1), and the recording sensitivity, modulation factor, and jitter with respect to fluctuations in the recording / reproducing wavelength due to individual differences of lasers, environmental temperature changes, etc. There has been a problem that recording characteristics such as error rate, reflectivity, etc. vary greatly.
On the other hand, in order to reduce the cost and labor of dye development, an optical recording medium in which the absorption maximum of the dye is longer than the wavelength of the writing light is described in Patent Document 21. Differences from the invention will be described later.
[0005]
[Patent Document 1]
JP 2001-181524 A
[Patent Document 2]
JP 2001-158865 A
[Patent Document 3]
JP 2000-343824 A
[Patent Document 4]
JP 2000-343825 A
[Patent Document 5]
JP 2000-335110 A
[Patent Document 6]
Japanese Patent Application Laid-Open No. 11-221964
[Patent Document 7]
Japanese Patent Laid-Open No. 11-334206
[Patent Document 8]
JP 2000-43423 A
[Patent Document 9]
JP-A-11-58955
[Patent Document 10]
JP 2001-39034 A
[Patent Document 11]
JP 2000-149320 A
[Patent Document 12]
JP 2000-113504 A
[Patent Document 13]
JP 2000-108513 A
[Patent Document 14]
JP 2000-222772 A
[Patent Document 15]
JP 2000-218940 A
[Patent Document 16]
JP 2000-222771 A
[Patent Document 17]
JP 2000-158818 A
[Patent Document 18]
JP 2000-280621 A
[Patent Document 19]
JP 2000-280620 A
[Patent Document 20]
Japanese Patent Laid-Open No. 2001-146074
[Patent Document 21]
JP 2002-74740 A
[0006]
[Problems to be solved by the invention]
Conventionally, high-to-low recording polarity is a common sense particularly in a write-once type optical recording medium. Therefore, it is necessary to select an organic material such as a dye having the same complex refractive index as in the past. However, as described above, in the recording / reproducing wavelength region below the blue laser wavelength, the complex refractive index equivalent to the red laser wavelength region is used. It is very difficult to realize. Even when an organic material having a complex refractive index equivalent to that of the red laser wavelength region exists in the recording / reproducing wavelength region below the blue laser wavelength, it is not possible to optimize the complex refractive index of the organic material to the recording / reproducing wavelength. It is very difficult.
This is because, in general, organic materials for short wavelengths have a small molecular skeleton, so that there are few parts that can introduce donors and substituents having an acceptor effect, and even if the molecular skeleton is large, the conjugated system is short. This is because the effect of the substituent having an acceptor effect is not sufficiently exhibited.
[0007]
In the conventional case, in order to realize the high-to-low recording polarity, for example, the absorption band of the organic material layer is positioned on the short wavelength side with respect to the recording / reproducing wavelength, and the recording / reproducing wavelength is set to the absorption band. However, under this condition, the recording / reproducing operation is performed against the problem that the organic material layer has to be designed each time by selecting the recording / reproducing wavelength, or the laser wavelength fluctuation during recording / reproducing. There was a problem that the characteristics changed significantly.
Accordingly, an object of the present invention is to provide a write-once type optical recording medium as described in the following a) to c).
B) A write-once type optical recording medium that is excellent in productivity capable of recording / reproducing even at a recording / reproducing wavelength of 500 nm or less, particularly in a wavelength region near 405 nm (which can be produced with good productivity).
B) A write-once type optical recording medium with little change in recording characteristics such as recording sensitivity, modulation degree, jitter, error rate, and reflectivity with respect to fluctuations in recording and reproducing wavelength
C) A write-once type optical recording medium that can be recorded in both the groove and the groove.
[0008]
[Means for Solving the Problems]
The above problems are solved by the following inventions 1) to 15).
1) A structure in which an organic material layer having a light absorption function sufficient to realize recording at a recording / reproducing wavelength and a reflective layer are sequentially provided on a substrate, and the recording polarity is low to high. A write-once optical recording medium that can be recorded and reproduced with light having a wavelength of 500 nm or less.
2) A structure in which a reflective layer, an organic material layer having a light absorption function sufficient to realize recording at a recording / reproducing wavelength, and a cover layer are sequentially provided on a substrate, and the recording polarity is low-to-two. A write-once optical recording medium that is high and can be recorded and reproduced by light having a wavelength of 500 nm or less.
3) The write-once type optical recording medium according to 1) or 2), wherein a heat insulating layer is provided between the organic material layer and the reflective layer.
4) Thermal insulation layer is SiO ₂ , ZnS · SiO ₂ , ZrO ₂ The write-once type optical recording medium according to 3), which is made of a material containing any of the above as a main component.
5) Thermal insulation layer is ZnS, ZrO ₂ , Y ₂ O ₃ And SiO ₂ The write-once type optical recording medium according to 3).
6) Thermal insulation layer is ZrO ₂ TiO ₂ , SiO ₂ And X, where X is Al ₂ O ₃ , MgO, CaO, NbO, Y ₂ O ₃ The write-once type optical recording medium according to 3), which is at least one selected from CeO.
7) The organic material in the organic material layer has an absorption band whose main absorption band is located on the longer wavelength side with respect to the recording / reproducing wavelength and has an absorption band that does not belong to the main absorption band in the vicinity of the recording / reproducing wavelength. The write-once type optical recording medium according to any one of the above.
8) Write-once light having a structure in which an organic material layer and a light absorption layer adjacent to the organic material layer are provided on a substrate, recording polarity is low-to-high, and recording / reproduction can be performed with light having a wavelength of 500 nm or less. recoding media.
9) The write-once type optical recording medium according to 8), which has a structure in which a light absorption layer, an organic material layer, and a reflective layer are sequentially provided on a substrate.
10) The write-once type optical recording medium according to 8), which has a structure in which a reflective layer, an organic material layer, a light absorbing layer, and a cover layer are sequentially provided on a substrate.
11) Any one of complex refractive index change, volume change, and cavity is generated in the organic material layer by the light absorption function of the light absorption layer, and the recording polarity becomes low to high. The write-once type optical recording medium as described.
12) The write-once type optical recording medium according to any one of 8) to 10), wherein the light absorption layer is deformed and the recording polarity becomes low-to-high due to the light absorption function of the light absorption layer.
13) The write-once type optical recording medium according to any one of 8) to 12), wherein the main absorption band of the organic material in the organic material layer is located on the long wavelength side with respect to the recording / reproducing wavelength.
14) Further, the organic material in the organic material layer satisfies the relationship of (light absorption function of the organic material layer at the recording / reproducing wavelength) <(light absorption function of the light absorbing layer at the recording / reproducing wavelength) 13) Optical recording medium.
15) The write-once type optical recording medium according to any one of 1) to 14), wherein the substrate has a guide groove and a recording part is formed in both the groove part (groove) and the groove part (land).
[0009]
Hereinafter, the present invention will be described in detail.
Conventionally, high reflectivity has been required for write-once type optical recording media. This is because compatibility with the ROM has been emphasized.
However, in the optical recording medium corresponding to the blue laser wavelength currently being developed, a rewritable optical recording medium using phase change has been developed ahead of ROM, and the rewritable optical recording medium is It is a standard medium in the blue wavelength region.
This rewritable optical recording medium generally has a low reflectance of about 10% or less. Therefore, in the short wavelength region below the blue laser wavelength, the problem of increasing the reflectance is no longer important. Also, in the short wavelength region below the blue laser wavelength, the reflectivity of the reflective layer itself also decreases, so even when a ROM is realized, it cannot be expected to have a high reflectivity as in the prior art.
Therefore, the present invention proposes to make the recording polarity of the write-once optical recording medium low to high at a recording / reproducing wavelength of blue laser wavelength or less (500 nm or less).
[0010]
The technique described in Patent Document 21 described above realizes a write-once type optical recording medium in which the relationship between a conventional dye (organic compound) and a recording / reproducing wavelength is reversed, but this technique uses a main absorption band of the dye. The recording / reproducing wavelength is adjusted to the bottom of the short wavelength side, and it is not easy to match the dye to the recording / reproducing wavelength (see FIG. 2). In this technique, there is no description about the recording polarity, and the technical idea is different from the present invention.
In the first aspect of the present invention, the recording / reproducing wavelength is not set to the main absorption band, but is set in the vicinity of the absorption band which is not attributed to the main absorption band and is shorter than the main absorption band ( (See Fig. 3. The recording / reproducing wavelength is set in the shaded area in the figure).
In other words, there is an absorption band that does not belong to the main absorption band in the vicinity of the recording / reproducing wavelength (an absorption band having a smaller absorption function than the main absorption band and a broad spectrum), and the main absorption is on the longer wavelength side than this absorption band. An organic compound having a band is used (see FIG. 3).
[0011]
In addition, as shown in FIG. 4, the “main absorption band” in the present invention refers to the absorption band having the largest absorption in the visible range, and generally refers to the transition of HOMO-LUMO (homomo-Lumo). Refers to the absorption band based on.
Therefore, for example, a dye (organic material) having an absorption spectrum as shown in FIG. 5 has the largest absorption band in a wavelength region of 300 nm or less, but in the present invention, this absorption band is not called a main absorption band. The absorption band near 700 nm (the largest absorption band in the visible range) is called the main absorption band.
The “absorption band not belonging to the main absorption band and located on the shorter wavelength side than the main absorption band” in the present invention is an absorption band based on a transition different from the main absorption band as shown in FIG. (Not an absorption band based on the HOMO-LUMO transition).
[0012]
In the present invention, the recording polarity is made low-to-high, and the merits include the following a) to d).
B) Since there is no need to finely control the positional relationship between the main absorption band and the recording / reproducing wavelength of the organic material, a general dye that has been studied for CD-R, DVD-R, etc., or a compound that can be easily synthesized is used. Is possible.
B) The layer structure is the same as that of a conventional write-once type optical recording medium, or only a heat insulating layer is added, and the structure of the optical recording medium is simple.
C) Since the recording / reproducing wavelength is not set near the main absorption band of the organic material, it is easy to shorten the wavelength (the degree of freedom in selecting the recording / reproducing wavelength is great).
D) Changes in recording characteristics such as recording sensitivity, modulation factor, jitter, and error rate, and changes in reflectivity can be reduced in response to fluctuations in the recording / reproducing wavelength (absorption function of the main absorption band having a large absorption coefficient) (This is because the complex refractive index fluctuation of the organic material near the recording / reproducing wavelength is small.)
[0013]
In the first aspect of the present invention, an organic material layer having a light absorption function sufficient to realize recording with respect to a recording / reproducing wavelength, a reflective layer on a substrate in order to make the recording polarity low to high The optical recording medium configuration in which is sequentially provided, or the light on which the reflective layer, the organic material layer having a light absorption function sufficient to realize recording with respect to the recording / reproducing wavelength, and the cover layer are sequentially provided on the substrate. Adopt recording medium configuration.
In this optical recording medium configuration, the layers other than the organic material layer do not have a light absorbing function for realizing recording, and therefore the organic material layer needs to bear the main light absorbing function.
The organic compound that can be used in the present invention is not limited as long as it has a light absorption function sufficient to realize recording with respect to the recording / reproducing wavelength, but low-to-high recording can be easily performed. In order to realize this, it is preferable to use an organic material whose main absorption band is located on the longer wavelength side with respect to the recording / reproducing wavelength and has an absorption band that does not belong to the main absorption band in the vicinity of the recording / reproducing wavelength.
[0014]
An absorption band that does not belong to the main absorption band and exists in the vicinity of the recording / reproducing wavelength needs to have a light absorption function sufficient to realize recording.
For example, in the dye (organic material) having the absorption spectrum of FIG. 5, the absorption band that does not belong to the main absorption band has sufficient light absorption ability to realize recording, but has the absorption spectrum of FIG. In a dye (organic material), an absorption band that does not belong to the main absorption band is shifted from the recording / reproducing wavelength region, and does not have sufficient light absorption capability to realize recording (the broken line region in FIGS. 5 and 8). Is a recording / reproducing wavelength range including a fluctuation range centering on a blue laser wavelength of 405 nm which is currently in practical use).
Therefore, an organic material layer having a light absorption function sufficient to realize recording with respect to the recording / reproducing wavelength on the substrate, an optical recording medium configuration in which a reflective layer is sequentially provided, or a reflective layer on the substrate, In the case of adopting an optical recording medium configuration in which an organic material layer having a light absorption function sufficient to realize recording at a recording / reproducing wavelength and a cover layer are employed in sequence, as the organic material layer, for example, as shown in FIG. It is preferable to use an organic material having a good absorption spectrum.
[0015]
By using an organic material having an absorption band that does not belong to the main absorption band in the vicinity of the recording / reproducing wavelength, the main absorption band is positioned on the long wavelength side with respect to the recording / reproducing wavelength as the organic material layer. Since the low-to-high configuration can be realized and the organic material layer has a main light absorption function, the configuration of the optical recording medium can be simplified.
In the first aspect of the present invention described above, the recording portion is formed by the following recording principles (a) to (d) by the light absorption function of the organic material layer.
B) Deform the substrate.
B) Changing the complex refractive index of the organic material layer.
C) Change the volume of the organic material layer.
D) A cavity is formed in the organic material layer.
However, in the present invention, not only the first aspect but also “an organic layer having an absorption band that is located on the long wavelength side with respect to the recording / reproducing wavelength and does not belong to the main absorption band in the vicinity of the recording / reproducing wavelength”. A second embodiment in which the “material” is not necessarily used is also included.
[0016]
In the second aspect of the present invention, an optical recording medium configuration having a structure in which a light absorption layer and an organic material layer are adjacent to each other on a substrate is employed in order to make the recording polarity low to high.
In this optical recording medium configuration, the main light absorption function can be assigned to the light absorption layer, and the main light absorption function can be removed from the organic material layer, thus greatly increasing the degree of freedom in selecting the organic material. be able to.
In this optical recording medium configuration, as described above, as the organic material, “the main absorption band is located on the long wavelength side with respect to the recording / reproducing wavelength, and there is an absorption band that does not belong to the main absorption band in the vicinity of the recording / reproducing wavelength. Not only can “organic material” be selected, but any organic material can be used. That is, there is no major limitation on the positional relationship between the recording / reproducing wavelength and the absorption band of the organic material layer, the absorption function of the organic material layer in the recording / reproducing wavelength region, and the like.
For example, it is possible to use an organic material having an absorption spectrum as shown in FIG. 8 that hardly absorbs in the recording / reproducing wavelength region.
However, in order to increase the reflectance at the time of non-recording and to improve the recording / reproducing characteristics, (light absorption function of the organic material layer at the recording / reproducing wavelength) <(light absorption function of the light absorbing layer at the recording / reproducing wavelength) It is preferable to satisfy this relationship.
[0017]
In this optical recording medium configuration, since a light absorbing layer is added to a write-once type optical recording medium using a conventional organic material, a recording principle such as deformation of the light absorbing layer that has not been possible in the past can be used. Low to high recording polarity can be realized more easily.
As a specific example of an optical recording medium configuration having a structure in which a light absorption layer and an organic material layer are adjacent to each other on a substrate, light having a structure in which a light absorption layer, an organic material layer, and a reflection layer are sequentially provided on the substrate is used. Examples include a recording medium or an optical recording medium having a structure in which a reflective layer, an organic material layer, a light absorption layer, and a cover layer are sequentially provided on a substrate.
In the second aspect of the present invention described above, the recording part is formed by the recording principle of the following a) to e) by the light absorption function of the light absorption layer.
B) Deform the light absorption layer.
B) Deform the substrate.
C) Changing the complex refractive index of the organic material layer.
D) Changing the volume of the organic material layer.
E) A cavity is formed in the organic material layer.
However, even if the above conditions are satisfied, it is not always possible to make the recording polarity low-to-high, and it goes without saying that the thickness and complex refractive index of each layer need to be optimized as appropriate.
[0018]
In the present invention,
B) Select an organic material whose main absorption band is on the long wavelength side with respect to the recording / reproducing wavelength, or the main absorption band is located on the long wavelength side with respect to the recording / reproducing wavelength, Select an organic material having an absorption band that does not belong to the main absorption band,
B) providing a light absorption layer adjacent to the organic material layer;
This eliminates the need to maintain the relationship between the absorption spectrum of the organic material and the recording / reproducing wavelength as in the past, and the recording characteristics such as recording sensitivity, modulation degree, jitter, error rate, etc. Changes in reflectance and the like can be greatly reduced as compared with the prior art (see FIG. 3). The relationship between the absorption spectrum and the recording / reproducing wavelength of a conventional write-once optical recording medium is shown in FIGS. In the recording medium, the change in the complex refractive index near the recording / reproducing wavelength becomes very gradual).
[0019]
Furthermore, in the first aspect of the present invention, a heat insulating layer may be provided between the organic material layer and the reflective layer in order to efficiently generate a complex refractive index change or volume change of the organic material layer and improve recording sensitivity. preferable. This heat insulating layer not only bears a so-called heat insulating effect, but can also be used to control the reflectance when not recorded or to control the degree of modulation.
In a write-once type optical recording medium using a conventional organic material layer, the organic material layer is generally formed by a spin coating method, so that the film thickness of the organic material layer is greater than (thickness of the groove)> (inter-groove portion). Film thickness). Further, only the organic material has a light absorption function, and the organic material causes a change in optical constant and the like to generate a main degree of modulation.
Therefore, even if good recording can be performed in the groove portion, the organic material layer film thickness becomes thin in the groove portion, so that the light absorption function is reduced and the phase difference change amount due to the recording is reduced. Recording is not possible (especially, in the groove portion of the optical recording medium in which the organic material layer and the reflective layer are sequentially laminated on the substrate, the temperature in the organic material layer only forms the recording portion due to the high thermal conductivity of the reflective layer. Temperature is difficult to reach).
[0020]
However, it is possible to obtain the same recording / reproducing characteristics at the inter-groove portion as that of the groove portion by applying the organic material layer to the vapor deposition method or applying the spin coating method with optimized coating conditions.
On the other hand, in the first aspect of the present invention, since the heat insulating layer is introduced between the organic material and the reflective layer, the thickness of the organic material layer becomes thin at the inter-groove portion, so that a sufficient light absorption function cannot be secured. The heat insulating layer can suppress the diffusion of heat from the reflective layer, and the organic material layer can be raised to a temperature at which the recording portion can be formed. As a result, the recording part can be formed not only in one of the groove part and the inter-groove part but in both.
It should be noted that the recording / reproducing characteristics such as recording sensitivity and modulation degree may be different between the groove and the portion between the grooves (not necessarily the same).
[0021]
In the second aspect of the present invention, the light absorbing layer is provided adjacent to the organic material layer except for the main light absorbing function from the organic material layer that has conventionally been responsible for the light absorbing function.
As will be described later, the light absorption layer of this optical recording medium is made of a material such as ceramics, metal, or semimetal, and is usually formed by sputtering or vapor deposition. There is no difference in function.
Therefore, for example, in an optical recording medium in which an organic material layer formed by spin coating is provided on a light absorbing layer, a difference in modulation degree or the like is caused by a difference in film thickness of the organic material layer between the groove and the groove. Although it may occur, a recording part can be easily formed in the inter-groove part and the groove part. Therefore, the density can be easily increased.
However, as described above, in the present invention, the recording part may be formed only in one of the groove part and the groove part.
[0022]
The optical recording medium of the present invention basically comprises a substrate or a substrate and a cover layer, an organic material layer, a heat insulating layer, a reflective layer, or a substrate or a substrate and a cover layer, an organic material layer, a light absorbing layer, and a reflective layer. However, if necessary, an undercoat layer, an overcoat layer, a protective layer, and the like may be provided.
The substrate material may be basically transparent to the recording light and the reproduction light.
Examples of such materials include acrylic resins, methacrylic resins, polycarbonate resins, polyolefin resins (particularly amorphous polyolefins), polyester resins, polystyrene resins, epoxy resins and other resins, glass, and photocurable resins on glass. What provided the resin layer which consists of radiation curable resin etc. can be used. Among these, injection molded polycarbonate is preferable from the viewpoint of high productivity, cost, moisture absorption resistance, and the like, and amorphous polyolefin is preferable from the viewpoint of chemical resistance, moisture absorption resistance, and the like. Moreover, a glass substrate is preferable from the viewpoints of high-speed response or no generation of voids.
A resin substrate or a resin layer may be provided in contact with the organic material layer or the light absorption layer, and guide grooves or pits for recording / reproducing light may be provided on the resin substrate or the resin layer.
[0023]
A preferred example of the organic material used for the organic material layer is a dye.
Examples of the dye include metal-containing azo dyes, phthalocyanine dyes, naphthalocyanine dyes, cyanine dyes, azo dyes, squarylium dyes, metal-containing indoaniline dyes, triarylmethane dyes, merocyanine dyes, and azurenium dyes. Naphthoquinone dyes, anthraquinone dyes, indophenol dyes, xanthene dyes, oxazine dyes, pyrylium dyes, and the like.
In addition, the organic material layer has a transition metal chelate compound (for example, acetylacetonate chelate, bisphenyldithiol, salicylaldehyde oxime, bisdithio-α-diketone as a singlet oxygen quencher in order to improve stability and light resistance of the organic material. Etc.) and a recording sensitivity improver such as a metal compound may be contained for improving the recording sensitivity.
Here, the metal compound means a compound in which a metal such as a transition metal is contained in the compound in the form of atoms, ions, clusters, etc., for example, ethylenediamine complex, azomethine complex, phenylhydroxyamine complex, phenanthroline complex, Organic metal compounds such as dihydroxyazobenzene complex, dioxime complex, nitrosoaminophenol complex, pyridyltriazine complex, acetylacetonate complex, metallocene complex and porphyrin complex can be mentioned. Although it does not specifically limit as a metal atom, It is preferable that it is a transition metal.
Moreover, the pigment | dye of another system | strain can also be used together as needed.
[0024]
Furthermore, a binder, a leveling agent, an antifoaming agent, etc. can also be used together as needed.
Preferable binders include polyvinyl alcohol, polyvinyl pyrrolidone, nitrocellulose, cellulose acetate, ketone resin, acrylic resin, polystyrene resin, urethane resin, polyvinyl butyral, polycarbonate, polyolefin and the like.
The film thickness of the organic material layer is not particularly limited because an appropriate film thickness varies depending on the recording method or the like, but is usually 50 to 300 nm.
Examples of the method for forming the organic material layer include a generally used thin film forming method such as a vacuum deposition method, a sputtering method, a doctor blade method, a casting method, a spin coating method, and an immersion method. The spin coating method is preferable from the viewpoint of mass productivity and cost, and the vacuum evaporation method is more preferable than the coating method from the viewpoint that a recording layer having a uniform thickness can be obtained.
[0025]
In the case of film formation by a spin coating method, the number of rotations is preferably 500 to 15000 rpm, and after spin coating, a treatment such as heating or exposure to solvent vapor may be performed.
The coating solvent for forming the recording layer by a coating method such as a doctor blade method, a casting method, a spin coating method, or a dipping method may be any solvent that does not attack the substrate and is not particularly limited.
For example, ketone alcohol solvents such as diacetone alcohol and 3-hydroxy-3-methyl-2-butanone; cellosolv solvents such as methyl cellosolve and ethyl cellosolve; chain hydrocarbon solvents such as n-hexane and n-octane Cyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, ethylcyclohexane, dimethylcyclohexane, n-butylcyclohexane, tert-butylcyclohexane and cyclooctane; perfluoroalkyl alcohols such as tetrafluoropropanol, octafluoropentanol and hexafluorobutanol Examples of the solvent include hydroxycarboxylic acid ester solvents such as methyl lactate, ethyl lactate, and methyl isobutyrate.
In addition, as the organic material layer, a polymer material, a phase change material, a photochromic material, a thermochromic material, or the like can be preferably used.
[0026]
As the light absorption layer, it is preferable to use a layer having a certain absorption coefficient with respect to the recording / reproducing wavelength in terms of ensuring sufficient recording sensitivity. ₄ Carbon-based non-oxides such as C, TiC, WC; carbon-based non-oxides such as amorphous carbon, graphite, diamond, ceramics typified by ferrite, etc .; Te-TeO ₂ , Te-TeO ₂ -Pd, Sb ₂ Se ₃ / Bi ₂ Te ₃ , Ge-Te-Sb-S, Te-TeO ₂ -Ge-Sn, Te-Ge-Sn-Au, Ge-Te-Sn, Sn-Se-Te, Sb-Se-Te, Sb-Se, Ga-Se-Te, Ga-Se-Te-Ge, In -Se, In-Se-Tl-Co, Ge-Sb-Te, In-Se-Te, Ag-In-Sb-Te, Ag-Zn, Cu-Al-Ni, In-Sb, In-Sb-Se Phase change recording materials such as In-Sb-Te; pure metals such as nickel, chromium, titanium and tantalum; alloys such as copper / aluminum and nickel / iron; semimetals such as silicon; and semiconductors such as Ge Is possible.
Among them, it is preferable to use a material containing Si and Ge as the light absorption layer, and for example, Si, Ge, SiC and the like are preferable examples.
The film thickness of the light absorption layer is usually 5 to 150 nm.
[0027]
As the heat insulating layer, for example, Al ₂ O ₃ , MgO, BeO, ZrO ₂ , UO ₂ , ThO ₂ Simple oxide based oxides such as SiO ₂ 2MgO · SiO ₂ , MgO / SiO ₂ , CaO · SiO ₃ , ZrO ₂ ・ SiO ₂ 3Al ₂ O ₃ ・ 2SiO ₂ 2MgO · 2Al ₂ O ₃ ・ 5SiO ₂ , Li ₂ O ・ Al ₂ O ₃ ・ 4SiO ₂ Silicate oxides such as Al ₂ TiO ₅ , MgAl ₂ O ₄ , Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , BaTiO ₃ LiNbO ₃ , PZT = Pb (Zr, Ti) O ₃ , PLZT = (Pb, La) (Zr, Ti) O ₃ , Ferrite and other complex oxides; Si ₃ N ₄ , Si _6-Z Al _Z O _Z N _8-Z Non-oxides of nitrides such as AlN, BN, TiN; SiC, B ₄ Non-oxides of carbides such as C, TiC and WC; LaB ₆ TiB ₂ , ZrB ₂ Non-oxides of borides such as CdS, MoS ₂ Sulfide non-oxide such as MoSi ₂ Silicide-based non-oxides such as amorphous carbon, graphite, diamond and other carbon-based non-oxides can be used.
From the viewpoint of transparency and productivity for recording / reproducing light, SiO ₂ Main component (main component) or ZnS / SiO ₂ As a preferred example, the main component (main component) is used. In order to obtain a sufficient heat insulation effect, ZrO ₂ It is also preferable to use as a main component (main component). Here, the main component means to occupy 50% by weight or more of the entire heat insulating layer material.
Furthermore, ZnS, ZrO ₂ , Y ₂ O ₃ , SiO ₂ An oxide comprising or ZrO ₂ TiO ₂ , SiO ₂ And X, where X is Al ₂ O ₃ , MgO, CaO, NbO, or Y ₂ O ₃ A material that is at least one selected from rare earth oxides such as CeO is also preferable.
The thickness of the heat insulation layer is usually about 5 to 200 nm.
[0028]
On the organic material layer, a reflective layer may be formed directly or through a heat insulating layer, an overcoat layer, or the like, and the preferred film thickness is 50 to 300 nm.
As a material of the reflective layer, a material having a sufficiently high reflectance at the wavelength of the reproduction light, for example, a metal such as Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Cr, Pd, alone or an alloy Can be used. Among them, Au, Al, and Ag have high reflectivity and are suitable as a material for the reflective layer.
Further, the above metal may be included as a main component and other elements may be included. Examples of other elements include Mg, Se, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Mention may be made of metals and semi-metals such as Cu, Zn, Cd, Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi.
Among these, those containing Ag as a main component are particularly preferable because they are inexpensive and easily provide high reflectivity.
It is also possible to form a multilayer film by alternately stacking a low refractive index thin film and a high refractive index thin film using a material other than metal, and use it as a reflective layer.
Examples of the method for forming the reflective layer include sputtering, ion plating, chemical vapor deposition, and vacuum vapor deposition.
Also, a known inorganic or organic overcoat layer, undercoat layer, or adhesive layer is provided on the substrate or under the reflective layer in order to improve reflectivity, improve recording characteristics, improve adhesion, etc. You can also.
[0029]
The material for the protective layer formed on the reflective layer is not particularly limited as long as it protects the reflective layer from external force. Examples of the organic material include a thermoplastic resin, a thermosetting resin, an electron beam curable resin, and a UV curable resin. In addition, as an inorganic material, SiO ₂ , SiN ₄ , MgF ₂ , SnO ₂ Etc.
Thermoplastic resins and thermosetting resins can be formed by applying a coating solution dissolved in a suitable solvent and drying.
The UV curable resin can be formed by applying a coating solution as it is or dissolved in an appropriate solvent, and curing by irradiating with UV light. As the UV curable resin, for example, acrylate resins such as urethane acrylate, epoxy acrylate, and polyester acrylate can be used.
These materials may be used alone or in combination, and may be used as a multilayer film as well as a single layer.
As a method for forming the protective layer, a coating method such as a spin coating method and a casting method, a sputtering method, a chemical vapor deposition method and the like are used as in the case of the recording layer. Among these, a spin coating method is preferable.
The thickness of the protective layer is generally in the range of 0.1 to 100 μm, but is preferably 3 to 30 μm in the present invention.
Further, a substrate may be further bonded to the reflective layer surface, or two optical recording media may be bonded to each other with the reflective layer surfaces facing each other.
An ultraviolet curable resin layer, an inorganic thin film, or the like may be formed on the mirror surface side of the substrate in order to protect the surface and prevent the adhesion of dust.
[0030]
The cover layer is necessary when using a lens with a high NA in order to increase the density.
For example, when the NA is increased, it is necessary to reduce the thickness of the portion through which the reproduction light is transmitted. This is due to the angle at which the disk surface deviates from the optical axis of the optical pickup as the NA increases (so-called tilt angle, proportional to the square of the product of the reciprocal of the wavelength of the light source and the numerical aperture of the objective lens). This is because the allowable amount of generated aberration is reduced, and this tilt angle is easily affected by the aberration due to the thickness of the substrate.
Therefore, the thickness of the substrate is reduced to minimize the influence of aberration on the tilt angle.
Therefore, for example, a recording layer is formed by forming irregularities on a substrate, a reflective layer is provided on the recording layer, and a light-transmitting cover layer, which is a thin film that transmits light, is provided on the recording layer. An optical recording medium that reproduces information on the recording layer by irradiating light, or a reflective layer provided on the substrate, a recording layer provided thereon, and a cover layer having optical transparency thereon. An optical recording medium that reproduces information on a recording layer by irradiating the reproducing light from the cover layer side has been proposed.
[0031]
In this way, the NA of the objective lens can be increased by reducing the thickness of the cover layer. That is, it is possible to further increase the recording density by providing a thin cover layer and recording / reproducing from the cover layer side.
Such a cover layer is generally formed of a polycarbonate sheet or an ultraviolet curable resin. Further, the cover layer referred to in the present invention may include a layer for adhering the cover layer.
The thickness of the cover layer is usually about 0.01 to 0.5 mm.
The laser beam used in the optical recording medium of the present invention is preferably as short as possible because of high-density recording. In particular, a laser beam having a wavelength of 350 to 530 nm is preferable, and a representative example thereof is a laser beam having a central wavelength of 405 nm. It is done.
[0032]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
[0033]
Example 1
On a substrate having a tracking guide groove having a groove depth of 55 nm, an organic material layer (average thickness of about 60 nm) composed of a dye represented by the following [Chemical Formula 1], an Ag reflecting layer (thickness 150 nm), an ultraviolet curable resin A write-once type optical recording medium in which a protective layer (thickness: 5 μm) made of the above was sequentially laminated was prepared.
The absorption spectrum of the dye represented by [Chemical Formula 1] is as shown in FIG. 5 and has an absorption spectrum suitable for CD-R.
Further, the dye represented by [Chemical Formula 1] is the “organic material having a light absorption function with respect to the recording / reproducing wavelength” as referred to in the present invention. It is an organic material having an absorption band that is located on the wavelength side and does not belong to the main absorption band in the vicinity of the recording / reproducing wavelength.
[Chemical 1]

[0034]
Using this optical recording medium, an optical disk evaluation device DDU-1000 (wavelength: 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd. was used to record in the groove (groove) under the following conditions. As a result, the recording polarity could be made low to high.

With this optical recording medium, the best jitter was obtained in the vicinity of a recording power of 7.5 mW, and a jitter (σ / Tw) of 9.5% was obtained.
Further, the eye pattern of the reproduced signal after equalization at this time is shown in FIG. 6, and it was confirmed that very good recording could be realized.
Further, FIG. 7 shows measurement results of jitter change and reproduction signal level change (reflectance change) of the unrecorded part (Δ) and the recorded part (■) when recording was performed with different recording power. As can be seen from FIG. 7, the recording contrast was sufficiently large and good jitter characteristics were obtained.
[0035]
Example 2
In order to confirm that the recording power for obtaining the best jitter is reduced by introducing the heat insulating layer and that good jitter is obtained, the heat insulation shown in Table 1 is provided between the dye layer (organic material layer) and the reflective layer. A write-once optical recording medium was produced in the same manner as in Example 1 except that the layer was inserted.
The optical recording medium was recorded in the groove (groove) in the same manner as in Example 1, and the optimum recording power and the best jitter were measured. The results are shown in Table 1.
The recording polarity was confirmed to be low to high.
Further, in the case of the optical recording medium of Example 1 in which the heat insulating layer was not introduced, recording at a level at which jitter could be measured in the recording power range of 11.0 mW or less could not be performed in the groove portion (land portion). It was confirmed that in the optical recording medium of the present example in which the layer was introduced, it was possible to perform recording capable of measuring jitter even between the grooves.
However, in this embodiment, the groove shape of the groove part and the groove part, the control of the coating state of the dye, or the film thickness of the dye layer is not optimized. In comparison, the optimum recording power increased by about 2.0 mW on average and the best jitter was also about 12.0%.
[Table 1]

[0036]
Example 3
On a substrate having a tracking guide groove having a groove depth of 55 nm, a light absorbing layer made of SiC (thickness 10 nm), an organic material layer made of a dye represented by [Chemical Formula 2] (average thickness about 60 nm), Ag reflection A write-once type optical recording medium in which a layer (thickness 150 nm) and a protective layer (thickness 5 μm) made of an ultraviolet curable resin were sequentially laminated was produced.
The absorption spectrum of the dye represented by [Chemical Formula 2] is as shown in FIG. 8 and has an absorption spectrum suitable for CD-R.
In addition, the dye of [Chemical Formula 2] hardly absorbs in the recording / reproducing wavelength region, and as stated in the present invention, “(light absorption function of the organic material layer at the recording / reproducing wavelength) <(light at the recording / reproducing wavelength”). It is an “organic material that satisfies the relationship of the light absorption function of the absorption layer”.
[Chemical 2]

Using this optical recording medium, an optical disk evaluation apparatus DDU-1000 (wavelength: 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd. is used to record in the groove portion (land portion) under the following conditions. Went.
As a result, the recording polarity was low to high, the best jitter was obtained in the vicinity of the recording power of 8.5 mW, and the jitter (σ / Tw) was 10.0%.
Further, the eye pattern of the reproduced signal after equalization at this time is almost the same as that in FIG. 6, and it was confirmed that very good recording can be realized.
Furthermore, the measurement result of the jitter change when recording was performed while changing the recording power is as shown in FIG. 9, and it was confirmed that good jitter characteristics were obtained.

[0037]
As is clear from the above examples, good recording / reproduction characteristics can be realized in the blue region even when a dye corresponding to the red laser wavelength as shown in [Chemical Formula 1] or [Chemical Formula 2] is used.
Further, as can be seen from the absorption spectra of the dyes of [Chemical Formula 1] and [Chemical Formula 2] (FIGS. 5 and 8), the change in the absorption coefficient in the blue laser wavelength region is gradual. , K) is also much smaller in wavelength dependency than in the prior art.
[0038]
【The invention's effect】
According to the present invention, recording / reproducing is possible even at a recording / reproducing wavelength of 500 nm or less, particularly in the wavelength region near 405 nm, and the productivity is excellent. Recording sensitivity, modulation degree, jitter, error rate with respect to fluctuations in the recording / reproducing wavelength Thus, it is possible to provide a write-once type optical recording medium that can record in both the groove part and the groove part.
[Brief description of the drawings]
FIG. 1 is a diagram showing that in a write-once type optical recording medium using a conventional organic material, fluctuation amounts δn and δk of a complex refractive index are very large with respect to a slight wavelength fluctuation amount δλ.
FIG. 2 is a diagram showing that the technique described in Patent Document 21 does not facilitate the matching of the dye to the recording / reproducing wavelength, as in the prior art.
FIG. 3 shows that the present invention does not match the recording / reproducing wavelength with the main absorption band, does not belong to the main absorption band, and is in the vicinity of the absorption band on the short wavelength side of the main absorption band (shaded area in the figure). The figure which shows setting a recording / reproducing wavelength.
FIG. 4 is a diagram for explaining a “main absorption band” in the present invention.
5 is a graph showing an absorption spectrum of a dye used in Example 1. FIG.
6 is a diagram showing an eye pattern of a reproduction signal of the write-once type optical recording medium of Example 1. FIG.
7 is a diagram showing measurement results of jitter change and change in an unrecorded part (Δ) and a recorded part (■) when recording is performed with different recording power in Example 1. FIG.
8 is a graph showing an absorption spectrum of a dye used in Example 3. FIG.
FIG. 9 is a diagram illustrating a measurement result of a jitter change when recording is performed by changing the recording power in the third embodiment.
[Explanation of symbols]
n Real part of complex refractive index
k Imaginary part of complex refractive index
δλ Wavelength variation
δn Variation of complex refractive index
δk Complex refractive index variation

Claims

On the substrate, it has a structure in which an organic material layer having a light absorption function sufficient to realize recording with respect to the recording / reproducing wavelength, a reflective layer, and a recording polarity is low to high. A write-once type optical recording medium capable of recording / reproducing with light having a wavelength of 500 nm or less.

The substrate has a structure in which a reflective layer, an organic material layer having a light absorption function sufficient to realize recording with respect to the recording / reproducing wavelength, and a cover layer are sequentially provided, and the recording polarity is low to high. A write-once type optical recording medium that can be recorded and reproduced by light having a wavelength of 500 nm or less.

The write-once type optical recording medium according to claim 1, further comprising a heat insulating layer between the organic material layer and the reflective layer.

The write-once type optical recording medium according to claim 3, wherein the heat insulating layer is made of a material mainly comprising any one of SiO ₂ , ZnS · SiO ₂ , and ZrO ₂ .

The write-once type optical recording medium according to claim _3, wherein the heat insulating layer is made of ZnS, ZrO ₂ , Y ₂ O ₃ and SiO ₂ .

The heat insulation layer is made of ZrO ₂ , TiO ₂ , SiO ₂ , and X, and X is at least one selected from Al ₂ O ₃ , MgO, CaO, NbO, Y ₂ O ₃ , and CeO. Write-once optical recording medium.

The organic material in the organic material layer has an absorption band whose main absorption band is located on the longer wavelength side with respect to the recording / reproducing wavelength and does not belong to the main absorption band in the vicinity of the recording / reproducing wavelength. The write once optical recording medium according to any one of the above.

Write-once type optical recording medium having a structure in which an organic material layer and a light absorption layer adjacent thereto are provided on a substrate, recording polarity is low-to-high, and recording / reproduction is possible with light having a wavelength of 500 nm or less .

The write-once type optical recording medium according to claim 8, which has a structure in which a light absorption layer, an organic material layer, and a reflection layer are sequentially provided on a substrate.

The write-once type optical recording medium according to claim 8, which has a structure in which a reflective layer, an organic material layer, a light absorption layer, and a cover layer are sequentially provided on a substrate.

The recording polarity is low-to-high due to any of complex refractive index change, volume change, and cavity in the organic material layer by the light absorption function of the light absorption layer. Write-once optical recording medium.

The write-once type optical recording medium according to any one of claims 8 to 10, wherein the light absorption layer is deformed and the recording polarity becomes low-to-high due to the light absorption function of the light absorption layer.

The write-once type optical recording medium according to any one of claims 8 to 12, wherein the main absorption band of the organic material in the organic material layer is located on the long wavelength side with respect to the recording / reproducing wavelength.

14. The write-once light according to claim 13, wherein the organic material in the organic material layer satisfies a relationship of (light absorption function of the organic material layer at the recording / reproducing wavelength) <(light absorption function of the light absorbing layer at the recording / reproducing wavelength). recoding media.

The write-once type optical recording medium according to claim 1, wherein the substrate has a guide groove, and a recording portion is formed in both the groove portion (groove) and the groove portion (land).