JP3883277B2 - Optical recording medium and manufacturing method thereof - Google Patents

Description

（式中、Ａはそれが結合している窒素原子及び炭素原子と一緒になって電子供与基または電子吸引基で置換されていても良い複素環を形成する残基を、Ｂはそれが結合している２つの炭素原子と一緒になって電子供与基で置換されていても良い芳香環を形成する残基を表し、Ｘは−ＯＨ基または−ＣＯＯＨ基を表す）
【００１１】
【発明の実施の形態】
以下に、本発明について詳細に説明する。
本発明の光記録媒体は、基本的に、グルーブを有する透明な基板上に、少なくとも記録層と反射層とを有するものである。本発明の光記録媒体の断面構成図を（図１）に示した。このように、本発明の光記録媒体は、基板、記録層、反射層及び保護層がこの順で積層された構造を有する。また、反射層の上に保護層および／または接着層を介して基板を貼り合わせた構造をとっても良い。また、基板と色素の間、色素と反射層の間、反射層と接着層との間、貼り合わせ用基板と接着層との間には他の層が存在していてもよい。
【００１２】
本発明の光記録媒体は、プリ・グルーブを有する基板上に形成された色素を含有してなる記録層が、下記式（１）〜（４）の条件を同時に満たすことを特徴とするものであり、このことにより、ＣＤよりも高密度のグルーブ記録を可能とした追記型光記録媒体である。
ｈ／ｄ ＞ ０．３ （１）
ｔｇ ≦ ｄ （２）
ｔｌ ＜ １００ｎｍ （３）
ｗｇ／ｗ＞ ０．５ （４）
（上式中、ｄはプリ・グルーブの深さ、ｗはプリ・グルーブの開口幅、ｔｇはグルーブ部の記録層の膜厚、ｔｌはランド部の記録層の膜厚、ｈはグルーブ部及びランド部に形成された記録層の表面段差、ｗｇはグルーブ開口部における記録層の表層幅を表す）
【００１３】
本発明の光記録媒体で用いる基板の材質としては、基本的には、記録及び再生で想定される６２０〜６９０ｎｍの波長光に対して透明であれば良い。例えば、アクリル樹脂、ポリエチレン樹脂、ポリカーボネート樹脂、ポリスチレン樹脂、ポリオレフィン樹脂、エポキシ樹脂等の有機高分子材料やガラス等の無機材料が利用される。この中で、基板の機械特性、グルーブ、プレピット等の成形のし易さ、また経済性の観点から、アクリル樹脂、ポリカーボネート樹脂、ポリオレフィン樹脂の射出成形基板が好ましく、特にＣＤ等で汎用的に使用実績のあるポリカーボネート樹脂基板がより好ましい。
【００１４】
なお、これら透明基板の形状は、板状でもフィルム状でもよく、また、円形やカード状でもよい。ＤＶＤ互換を考慮すれば、直径８０ｍｍもしくは１２０ｍｍのディスクで、中央に１５ｍｍ程度のセンターホールが形成された形状が望ましい。これらの基板表面には、通常、サブミクロンオーダーのグルーブ及び／又はプレピットが螺旋状または同心円状に形成されている。これら基板表面に存在するグルーブやプレピットは、基板成形時に付与されるのが好ましいが、基板の上に熱硬化性樹脂または紫外線硬化樹脂層を設けて付与することもできる。
【００１５】
ここで、グルーブ形状、特にグルーブ深さは、単にトラッキング案内溝としてサーボ安定性を支配するだけでなく、その上に形成される記録膜の成膜形状にも直接的または間接的な影響を及ぼすため、結果として記録特性への影響が無視しえない。安定なトラッキング性能を保持しながら、且つ、後述する記録層膜厚構成とのバランスを考慮したときには、最適な基板グルーブ深さｄは、１００ｎｍ〜３００ｎｍ、好ましくは１２０ｎｍ〜２００ｎｍの範囲である。
ここで、ｄ＞３００ｎｍでは、製造上、基板への溝転写がとりずらく現実的でないし、ｄ＜１００ｎｍでは、記録膜が基板グルーブ内部に密閉しづらくなり、良好な性能が保持し難い。
【００１６】
本発明の光記録媒体では、形成される記録膜の形状が特に重要である。すなわち、記録膜の形状に関しては、特にＣＤよりも高密度の記録を行った際のピットエッジを良好化させるために、基板グルーブ上にのみ、記録層を局在密閉さることが構造上、極めて重要である。
本発明の光記録媒体における成膜形状断面図を（図２）に示した。
記録層は、グルーブ部の記録層の膜厚（ｔｇ）を基板のプリ・グルーブ深さ（ｄ）よりも小さく成膜すること、
且つ、グルーブ部及びランド部に形成された記録層の表面段差（ｈ）をプリ・グルーブ深さ（ｄ）を基準にして大きく形成させること、
且つ、プリ・グルーブ開口幅（ｗ）に対して、形成された記録層のその部位での表層幅（ｗｇ）が極力大きく、グルーブからランド部位への記録層のはみ出しが小さいこと、がより細密記録ピットエッジ良好化のために必須となる。
また更に、ランド部の記録層膜厚（ｔｌ）の薄化は、記録層表層界面を介して反射層への熱伝播を速め、隣接トラック間の熱干渉を緩和させるため、グルーブ内への高密度記録ピットを密閉させるための必要条件となる。
【００１７】
本発明者らは、用いる基板のプリ・グルーブ条件及び記録層成膜条件〔塗布法であれば、回転条件、溶剤条件、環境条件（温度など）、蒸着方法等〕を変え、上記ｄ、ｈ、ｔｇ、ｔｌ、ｗｇを種々変更しながら定量的な検討を行った結果、下記の式（１）〜（４）を同時に満たす膜構造とすることで、高密度記録に良好な最短ピットが再現性良く得られることを見だした。
ｈ／ｄ ＞ ０．３ （１）
ｔｇ ≦ ｄ （２）
ｔｌ ＜ １００ｎｍ （３）
ｗｇ／ｗ＞ ０．５ （４）
【００１８】
本発明の光記録媒体において、ｔｇ≦ｄの制御は特に重要である。より好ましくは、ｈ／ｄ＞０．４、且つ、ｔｌ＜６０ｎｍの成膜構造である。
ｔｇ＞ｄ、ｈ／ｄ≦０．３の成膜構造は、トラック間のピット干渉（クロストーク）が顕在化し、高密度記録時の最短ピットジッターが大幅に悪化する傾向があり、また、ランド部の膜厚ｔｌ≧１００ｎｍでは、トラック間クロストークが無視し得なくなるため、好ましくない。同様に、ｗｇ／ｗ≦０．５では、やはりクロストークが大きくなり、信号劣化をきたす傾向があった。
ここで、基板および記録層の表面（界面）形状は、ＳＴＭまたはＡＦＭにて計測することができる。また、色素膜厚などは、成膜後の記録層断面形状として、液体窒素中で成膜基板サンプルの凍結破断面を作製し、断面ＳＥＭ像から計測可能である。もちろん、ｄｅｋｔａｃｋ段差計データなどでも定量化できる。
【００１９】
本発明の光記録媒体で記録層に用いる色素としては、着目する６２０ｎｍ〜６９０ｎｍのレーザー波長域において適度な吸収を有し、光・熱変換を伴って一定以上のエネルギーを持つレーザー光の照射で、物理的・化学的な変形、変質、分解を伴うような有機色素材料であれば基本的には何でも良い。ＤＶＤプレーヤでの再生互換を前提とした高密度記録を想定するにおいては、その色素材料の光学特性、即ち、λmax が５５０ｎｍ〜６００ｎｍ付近に存在し、上記想定レーザー波長域での屈折率ｎが大きく（ｎ≧１．９）、吸収が適切（減衰定数ｋ≦０．２５）なものが高反射率、高変調度を獲得する上で望ましい。ここで、ｎ＜１．９では、反射率に低下をきたしＤＶＤプレーヤー互換で問題をきたすし、また、ｋ＞０．２５であるとやはり反射率が極端に低下するし、再生光によるダメージも顕在化するため好ましくない。
【００２０】
また、熱特性の観点からは、色素材料の融点、分解点がともに２００℃以上であることが安定な高密度記録ピットを形成する上で必須である。このような具体的な色素としては、シアニン系、アゾ系、フタロシアニン系、ポルフィリン系、ジベンゾフラン系、インジゴ系等が提案されてきている。本発明では、良好な光学特性、熱特性、そして、耐久性能の観点から、下記一般式（Ｉ）（化３）で表されるモノアゾ化合物の金属錯体が特に好ましい。
【００２１】
【化３】

（式中、Ａはそれが結合している窒素原子及び炭素原子と一緒になって電子供与基または電子吸引基で置換されていても良い複素環を形成する残基を、Ｂはそれが結合している２つの炭素原子と一緒になって電子供与基で置換されていても良い芳香環を形成する残基を表し、Ｘは−ＯＨ基または−ＣＯＯＨ基を表す）
【００２２】
一般式（Ｉ）で表されるモノアゾ化合物の金属錯体において、Ａで表される複素環を形成する残基としては、例えば、チアゾール環、ベンゾチアゾール環、ピリドベンゾチアゾール環、ベンゾピリドチアゾール環、ピリドチアゾール環、ピリジン環、キノリン環、チアジアゾール環、イミダゾール環などが挙げられる。特に光学物性及び溶解性の観点では、ピリジン環またはチアジアゾール環が好ましくピリジン環が特に優れる。
これら複素環は、１つ以上の電子吸引基及び／又は電子供与基、さらには溶解性制御及び会合性制御を目的とする置換基で置換されていても良い。これらの置換基としては、具体的には、水素原子の他、炭素数１〜１０のアルキル基、アルコキシ基、アリール基、ハロゲン原子などがあげられる。もちろんこれらの置換基は更に置換基を有していても良い。
【００２３】
また、一般式（Ｉ）のＢで表される芳香環を形成する残基の例としては、ベンゼン環、ナフタレン環、ピリドン環、ピリジン環、ピラゾール環などがあげられる。好ましくはベンゼン環であり、少なくとも一つの電子供与基及び／又は溶解性、会合性制御を目的とする置換基で修飾されていることが好ましい。かかる置換基としては炭素数１〜１０のアルキル基、アルコキシ基、アミノ基などが上げられる。これらの置換基は更に置換基を有していても良い。
一般式（Ｉ）のＸとしては、活性水素を有する基であれば特に制限は無いが、好ましくは−ＯＨ基、−ＣＯＯＨ基が良い。
【００２４】
更に、配位される金属としては、アゾ化合物と錯体を形成する能力を有する金属であれば特に限定されない。安定性、光学特性からは、Ｎｉ、Ｃｏ、Ｆｅ、Ｍｎ、Ｐｄ、Ｃｕ、Ｚｎ等の遷移金属が好ましい。特に、Ｎｉ、Ｃｏ、Ｃｕが良好である。これらのアゾ系金属錯体化合物に関しては、単独でも複数の化合物を混合して用いても良い。なお、本発明に用いられるアゾ系の金属錯体は、例えば、古川 ; Analytica Chimica Acta 140 (1982) 281〜289 に記載の方法に準じて合成することができる。
【００２５】
また、記録層には、必要に応じて、樹脂やレベリング材、クエンチャー、色素熱分解促進剤、紫外線吸収剤などの添加剤を混合あるいは置換基として導入することも可能である。もちろん、本発明の有機色素は単独で用いても良いし、２種以上を混合して用いても良い。
【００２６】
次に、本発明の光記録媒体の製造方法について述べる。
本発明の光記録媒体において、記録層の形成方法としては、特に限定されるものではなく、スピンコーティング法やキャスト法等の塗布法、スプレー法、スパッタ法、化学蒸着法および真空蒸着法などが挙げられ、その最適化条件を適用して成膜される。
本発明の光記録媒体のポイントは、記録層を基板のプリ・グルーブ内へ密閉することであり、その製造に際しての成膜制御が極めて重要である。
【００２７】
本質的に、グルーブ形状に追従した成膜形成（ｈ／ｄ：大、ｗｇ／ｗ：大）、及び、条件制御によるグルーブ膜厚（ｔｇ）＜グルーブ深（ｄ）の達成が必須であるため、蒸着法、スパッタ法が本質的に好ましい。しかし、選択的にランド膜厚（ｔｌ）を小さく成膜できない上に、蒸着法では膜厚の精密管理が実質的に困難であり、また、スパッタ法では成膜過程でえてして色素の分解が生じるため、条件の精密制御が必要となり、結果的に現実性を帯びない難点もある。
本発明者らは、易生産法であるスピンコート法による成膜プロセスについて検討した結果、この方法でも、主として、溶剤、塗布回転条件、塗布環境条件（温度、風量等）等の最適化で、ｔｇ≦ｄ条件を満足し、上記成膜形状が十分制御しうることを見いだした。
【００２８】
塗布方式における基板グルーブ上の成膜形状制御では、特に塗布溶剤及び溶液濃度（粘度）の選択が非常に重要である。溶剤は、色素を溶解または分散しやすいもので、且つ、基板にダメージを与えないことが必須であり、さらに、前述した（１）〜（４）の条件を満足するためには、塗布溶剤蒸発速度の制御が特に重要であり、効果が大きい。本発明者らの詳細な検討によれば、塗布溶剤は、好ましくは、沸点７０℃〜１５０℃のもの、より好ましくは、８０℃〜１２０℃の範囲のものである。例えば、ランド部の記録層の膜厚（ｔｌ）の薄膜化は、低粘度で蒸発の遅い溶剤系の選択で容易に達成可能であり、一方、グルーブ部とランド部の記録層の表面段差（ｈ）を大きくするには、蒸発速度が大きく、寧ろ高粘度溶剤の適用が好ましい。
ここで双方のバランス取りは、混合溶剤の適用、色素溶解濃度の調製、回転条件に勾配を持たせることによる蒸発速度の制御、及び環境温度の調節、等で制御できる。塗布温度は２０〜３０℃、乾燥温度は５０〜１００℃程度が好ましい。
【００２９】
塗布溶剤としては、炭化水素系溶剤（ヘキサン、シクロヘキサン、オクタン、トルエン、キシレンなど）、アルコール系溶剤（メタノール、エタノール、プロパノール、イソプロパノールなど）、ハロゲン化アルコール系溶剤（２，２，３，３−テトラフルオロ−１−プロパノール、へプタフルオロブタノール、ペンタフルオロプロパノール、ヘキサフルオロイソプロパノール等）、ハロゲン化炭化水素系溶剤（クロロホルム、四塩化炭素、ジクロロジフオロエタン等）、エーテル系溶剤、セロソルブ系溶剤等が挙げられる。これらは、それぞれ、沸点、蒸気圧、粘度等を考慮して、単独で、あるいは複数を混合して用いられる。
特に、モノアゾ化合物の金属錯体の塗布の場合には、アルコール系溶剤とハロゲン化アルコール溶剤の混合系が有効である。
【００３０】
本発明の光記録媒体において、形成された記録層は、中間層を介して２層に積層することも可能であり、反射層のエンハンス効果を得る目的、および、記録特性改良の目的で、記録層と反射層の界面に、中間層として無機誘電体層、色素層などを多層積層させてやることもある。
【００３１】
反射層の材料としては、再生光の波長で反射率が十分高いもの、例えば、Ａｕ、Ａｌ、Ａｇ、Ｃｕ、Ｔｉ、Ｃｒ、Ｎｉ、Ｐｔ、Ｃｒなどの金属を、単独で、あるいは合金にして用いることが可能である。なかでもＡｕ、Ａｌ、Ａｇ、Ｃｕは反射率が高く最適である。
反射層の作製方法としては、例えば、スパッタ法、化学蒸着法、真空蒸着法、インプレーティング方法等が挙げられ、通常３０〜２００ｎｍの膜厚で成膜形成される。好ましくは５０〜１５０ｎｍである。また反射層の密着性を高める目的で記録層と反射層との間に接着層を設ける場合もある。
【００３２】
本発明の光記録媒体においては、記録層および反射層を保護するために、反射層の上に、更に公知技術により、定法たる保護層を設けたり、２枚の基板を貼り合わせてもよい。
保護層の材料は、記録層及び反射層を外力から保護するものであれば特に限定しない。有機物質としては、熱可塑性樹脂、熱硬化性樹脂、ＵＶ硬化性樹脂等を挙げることができる。なかでもＵＶ硬化樹脂が好ましい。
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などの塗布法が適用される。
本発明の光記録媒体では、保護層の上に更にレーベル等の印刷などを行うこともできる。また、基板鏡面側には、表面保護やゴミ等の付着防止のために紫外線硬化樹脂、無機薄膜を成膜してもよい。
【００３３】
本発明の光記録媒体に情報を記録する方法としては、例えば、光記録媒体を一定の線速度で回転させながら、透明基板側から該案内グルーブの底部にレーザー光を照射して案内溝上にある記録層に再生用のピットを形成して行う。信号としては、ＤＶＤと同一のＥＦＭ＋信号を記録し、その際のチャネルビットクロックに対するピットエッジゆらぎをジッターとして定量化することが、本発明の効果を評価する上で好ましい。
【００３４】
【実施例】
以下、実施例により本発明を具体的に説明するが、本発明の実施の態様はこれに限定されるものではない。
実施例１
スパイラル状のグルーブ（深さ１４０ｍｍ、幅０．３５μｍ、ピッチ０．７４μｍ）を有する厚さ０．６ｍｍ、直径１２０ｍｍの射出成形ポリカーボネート基板のグルーブを有する面に、下記式（II）（化４）で表されるモノアゾ化合物のＮｉ錯体を、２，２，３，３−テトラフルオロ−１−プロパノール（沸点１１０℃）とイソプロピルアルコール（沸点８０℃）の（９：１）混合溶剤に溶解し、２０ｇ／ｌの溶液を得た。回転数３００ｒｐｍから３０００ｒｐｍまで、９秒間の勾配を付けて、スピンコーティングし、当該グルーブ上に実質色素のみからなる記録層を成膜し、オーブン中、７０℃、２時間乾燥した。
【００３５】
【化４】

グルーブ部の記録層の膜厚（ｔｇ）、ランド部の記録層の膜厚（ｔｌ）、および、グルーブ部とランド部の記録層の表面段差（ｈ）を、表面形状はＡＦＭ、膜厚に関しては断面ＳＥＭにて計測した結果、、それぞれ、ｔｇ＝１００ｎｍ、ｔｌ＝５０ｎｍ、ｈ＝９０ｎｍ、ｗｇ＝０．２２μｍと測定された。
ｄ＝１４０ｎｍ、ｗ＝０．３５μｍであるので、ｈ／ｄ＝０．６４、ｗｇ／ｗ＝０．６３である。
【００３６】
次に、この記録層上に、バルザース製スパッタ装置（ＣＤＩ−９００）を用いてＡｕをスパッタし、厚さ８０ｎｍの反射層を形成した。更に反射層の上に、ＵＶ硬化性樹脂ＳＤー１７（大日本インキ化学工業製品）をスピンコートした後、ＵＶ照射して、厚さ３μｍの保護層を形成した。この上にＵＶ硬化樹脂ＳＤ−３０１（大日本インキ化学工業）を塗布し、この接着剤の上に、前記したと同じ０．６ｍｍ基板を重ね合わせ、高速で回転して余分の接着剤を除去した後、ＵＶ光を照射して貼り合わせた光記録媒体を作製した。
【００３７】
この光記録媒体をターンテーブルに乗せ、３．７ｍ／ｓの線速で回転させながら、波長＝６３９ｎｍのレーザー及びＮＡ＝０．６０の光ヘッドを搭載したパルステック工業製光ディスク評価装置（ＤＤＵ−１０００）及ぶＫＥＮＷＯＯＤ製ＥＦＭ＋エンコーダーを用いて、記録パワーを連続的に変化させながら、最短ピット長が０．４０μｍのＥＦＭ＋変調信号を記録した後、同じ装置を用いて、レーザー出力を０．５ｍＷにして記録信号の読み出しを行った。なお、信号再生時にはＤＶＤ再生基準に準拠したエコライゼーション処理を施した。この結果、ジッターは、チャネルビットクロックの８．１％を示した。この媒体は、例えば、松下電器産業製ＤＶＤプレーヤー（ＤＶＤ−Ａ３００）で良好に再生できた。
【００３８】
実施例２
塗布溶剤としてペンタフルオロプロパノールとオクタフルオロペンタノールの１：２混合溶剤を用いた以外は、実施例１と同様にして記録媒体を作製した。
記録層の形状を測定した結果、ｔｇ＝８０ｎｍ、ｔｌ＝６０ｎｍ、ｈ＝１２０ｎｍ、ｗｇ＝０．２５μｍであった。したがって、ｈ／ｄ＝０．８６、ｗｇ／ｗ＝０．７１であり、ジッターは、７．７％と良好であった。
【００３９】
実施例３
深さｄ＝１８０ｎｍ、開口幅ｗ＝０．３５μｍのグルーブを有するポリカーボネート基板を用いた以外は、実施例１と同様にして記録媒体を作製し、また、信号評価を行った。
記録層の形状は、ｔｇ＝１２０ｎｍ、ｔｌ＝３０ｎｍ、ｈ＝９０ｎｍ、ｗｇ＝０．２８μｍ（ｈ／ｄ＝０．５０、ｗｇ／ｗ＝０．８０）であった。この系でのジッターは７．２％であった。
【００４０】
実施例４
下記式(III）（化５）で表されるモノアゾ化合物のＮｉ錯体を用いた以外は、実施例１と同じ処方で記録媒体を作製し、信号評価を行った。
記録層の形状は、実施例１と同じであり、この時のジッター値は８．９％であった。
【００４１】
【化５】

【００４２】
比較例１
塗布回転条件を、８００ｒｐｍ、１５秒とした以外は、実施例１と同様にして記録媒体を作製し、信号評価を行った。
記録層の形状は、ｔｇ＝１８０ｎｍ、ｔｌ＝１００ｎｍ、ｈ＝６０ｎｍ（ｈ／ｄ＝０．４３）であった。ｔｇ＞ｄであるため、ｗｇ＝０となり、ｗｇ／ｗ＝０である。このときジッターは１６．５％となり大幅に悪化した。クロストークも５１％と非常に大きかった。
この媒体は前述した松下製ＤＶＤプレーヤでは再生不能であった。
【００４３】
比較例２
深さｄ＝５０ｎｍのグルーブを有するポリカーボネート基板を用いた以外は、実施例１と同様にして記録媒体を作製し、信号評価を行った。
ｔｇ＝９０ｎｍ、ｔｌ＝５５ｎｍ、ｈ＝１５ｎｍ（ｈ／ｄ＝０．３）であった。このとき、ジッターは１５．８％であった。また、トラッキングが非常に制御しずらかった。
【００４４】
比較例３
塗布溶剤として、２，２，３，３−テトラフルオロ−１−プロパノールとエチレングリコールの（２：１）溶剤を用い、１０ｇ／ｌの溶液を造り、塗布回転条件を８００ｒｐｍとした以外は実施例１と同様にして記録媒体を作製し、評価した。形状は、ｔｇ＝１００ｎｍ、ｔｌ＝６０ｎｍ、ｈ＝１００ｎｍ、ｗｇ＝０．１０μｍ（ｈ／ｄ＝０．７１、ｗｇ／ｗ＝０．２９）であり、ジッターレベルは１８．１％であった。
【００４５】
比較例４
下記式（IV）（化６）で表されるシアニン系色素を用いた以外は、実施例１と同様にして記録媒体を作製し、信号評価を行った。
形状は、ｔｇ＝１１０ｎｍ、ｔｌ＝４０ｎｍ、ｈ＝７０ｎｍ、ｗｇ＝０．２５μｍ（ｈ／ｄ＝０．５、ｗｇ／ｗ＝０．７１）であり、ジッターレベルは２０．１％と非常に劣悪であった。
【００４６】
【化６】

基板のグルーブ深さ、塗布溶剤、塗布回転条件を変えて、記録媒体を形成した上記の結果を表−１（表１）にまとめて示した。
【００４７】
【表１】

【００４８】
【発明の効果】
グルーブを有する透明な基板上に、少なくとも記録層及び反射層を有する光記録媒体において、深さｄ、開口幅ｗのプリ・グルーブを有する基板に、色素を含有する記録層を、特定の条件を満たすように形成させることにより、６２０ｎｍ〜６９０ｎｍのレーザー光を用いて、ＣＤよりも高密度な記録媒体を提供することを可能にした。
【図面の簡単な説明】
【図１】本発明の光記録媒体の断面構成図
【図２】本発明の光記録媒体の成膜形状断面図
【符号の説明】
１：基板
２：記録層
３：反射層
４：保護層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium, and more particularly to a write-once type optical recording medium capable of recording / reproducing with a red laser beam selected from a range of 620 nm to 690 nm and capable of recording at a higher density than a CD.
[0002]
[Prior art]
A recordable optical recording medium having a dye as a recording layer and a reflective layer provided on the recording layer for the purpose of obtaining reflectance is disclosed in, for example, Optical Data Storage 1989 Technical Digest Series Vol. 1, 45 (1989) A medium using a cyanine dye or a phthalocyanine dye in the recording layer is supplied to the market as a CD-R medium.
These media are characterized in that they can be recorded with a semiconductor laser of 780 nm and can be reproduced with a widely used commercial CD player or CD-ROM player. However, these media have a capacity of only 650 MB, and for recording large amounts of information, such as digital moving images, the recording time is as short as about 15 minutes, and it is possible to cope with the situation where the miniaturization of devices is progressing. In the meantime, if the medium is supposed to be downsized, the capacity is clearly insufficient.
[0003]
Under these circumstances, in recent years, a semiconductor laser with a wavelength of 620 nm to 690 nm has been developed, which enables higher density reproduction, and an optical recording medium on which a high-quality moving image of about 2 hours is recorded on the same size (120 mm diameter) as a CD is a DVD. Has been developed as. This medium has a recording capacity of 4.7 GB / surface and is a reproduction-only medium produced by transferring pits to a substrate. More recently, there is a strong demand for an optically recordable medium that has the same format as that of the read-only DVD and has a 4.7 GB recording capacity that can be reproduced by an existing DVD player. Against this backdrop, it may be optimal for DVD authoring verification, but as the red semiconductor laser increases in output, there is also an expectation as a successor to CD-R as a medium for storing large-capacity data in the future.
[0004]
However, in a recordable medium, it is necessary to narrow the recording laser beam in order to increase the recording capacity. It is preferable that the laser used has a shorter wavelength and that the numerical aperture (NA) of the objective lens is larger. However, due to the current semiconductor laser technology and lens NA, the beam diameter is naturally limited. For example, the beam diameter of the aforementioned DVD is not smaller than the recording density as compared with the conventional CD. For this reason, as the recording pit density increases, thermal interference and crosstalk between pits and tracks during recording increase, and fluctuations of pit edges (hereinafter referred to as jitter), which are particularly important for signal detection, increase. As a result, the error rate deteriorates. Therefore, in order to avoid such a problem, there is a demand for a high-density write-once medium capable of accurately recording and forming narrower and smaller pits with respect to the beam diameter farther than in the case of CD-R.
[0005]
Here, a recordable medium using a similar azo compound is disclosed in Japanese Patent Publication No. 5-67438. However, there is only a description of recording at a conventional near-infrared laser wavelength, and various requirements that become a problem when the recording density is increased are not disclosed.
In addition, with respect to an example using a similar azo compound in an application that assumes higher density recording than CD, JP-A-9-81966, JP-A-9-274732, etc. also include the structure related to the medium recording layer. There is a description. However, these are also descriptions of only the substrate groove shape and the shape of the recording layer thickness on the groove, and the mutual shape correlation including the recording layer thickness of the land portion and the coating film surface shape affects the recording characteristics. There is no specific description of the impact. In addition, when assuming a recording layer made of an organic dye premised on coating film formation, regarding the effect that the recording layer thickness formed on the groove is thinner than the groove depth of the substrate, There is no description at all including the manufacturing method, and there is no specific description regarding the shape of the interface between the recording layer made of an organic dye and the reflective layer.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problem, that is, in a medium having at least a recording layer and a light reflection layer containing a dye that absorbs laser light on a groove-containing transparent substrate, 620 nm to 690 nm. When pits smaller than the conventional recording beam diameter are formed using light of a wavelength selected from the above, good pit edge characteristics (jitter) are avoided by avoiding thermal interference and crosstalk between pits and tracks. It is an object of the present invention to provide a high-density write-once optical recording medium that achieves characteristics) and has good reproduction compatibility with a DVD player.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have made extensive studies for the purpose of obtaining a good recording pit jitter equivalent to 4.7 GB, which is the full capacity of one side of a DVD. As a result, the expected laser wavelength range of 620 to 690 nm In order to seal the recording pits locally on the substrate groove that actually becomes the recording site, the recording layer film formation shape is controlled, so that an effect for good high-density recording can be obtained. On the other hand, it has been found that a better effect can be obtained by selectively applying an organic dye material having good optical characteristics and thermal decomposition characteristics. That is, by controlling the substrate groove shape to be used, the groove thickness and land thickness of the recording layer formed by coating, and the interface shape between the recording layer and the reflective layer by a simple coating film forming method, By selectively applying a dye material containing a metal complex of a monoazo compound to the recording layer, it was found that a high-density recording pit edge smaller than the recording beam diameter was formed satisfactorily, and the present invention was achieved. It was.
[0008]
That is, according to the present invention, (1) an optical recording medium having at least a recording layer and a reflective layer is formed on a transparent substrate having a groove, and a recording layer containing a dye is formed on the substrate having a pre-groove. In addition, the present invention relates to a write-once type optical recording medium capable of groove recording at a higher density than a CD, wherein the recording layer simultaneously satisfies the following formulas (1) to (4).
h / d> 0.3 (1)
tg ≦ d (2)
tl <100nm (3)
wg / w> 0.5 (4)
(Where d is the depth of the pre-groove, w is the opening width of the pre-groove, tg is the film thickness of the recording layer in the groove portion, tl is the film thickness of the recording layer in the land portion, h is the groove portion and The surface step of the recording layer formed in the land portion, wg represents the surface layer width of the recording layer in the groove opening)
[0009]
Further, in the present invention, (2) the optical recording medium according to claim 1, wherein the recording layer contains a metal complex of a monoazo compound represented by the following general formula (I) (Formula 2):
(3) The method for producing an optical recording medium according to (1) or (2), wherein the recording layer is formed by a coating method.
[0010]
[Chemical 2]

(Wherein A is a residue that, together with the nitrogen and carbon atoms to which it is attached, forms a heterocycle that may be substituted with an electron donating or electron withdrawing group, and B is a bond to which Represents a residue which forms an aromatic ring which may be substituted with an electron donating group together with two carbon atoms in which X represents -OH group or -COOH group)
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The optical recording medium of the present invention basically has at least a recording layer and a reflective layer on a transparent substrate having grooves. A cross-sectional configuration diagram of the optical recording medium of the present invention is shown in FIG. Thus, the optical recording medium of the present invention has a structure in which the substrate, the recording layer, the reflective layer, and the protective layer are laminated in this order. Further, a structure in which a substrate is bonded to the reflective layer via a protective layer and / or an adhesive layer may be employed. Further, other layers may exist between the substrate and the dye, between the dye and the reflective layer, between the reflective layer and the adhesive layer, and between the bonding substrate and the adhesive layer.
[0012]
The optical recording medium of the present invention is characterized in that a recording layer containing a dye formed on a substrate having pre-grooves simultaneously satisfies the conditions of the following formulas (1) to (4). Thus, this is a write-once type optical recording medium that enables groove recording at a higher density than CD.
h / d> 0.3 (1)
tg ≦ d (2)
tl <100nm (3)
wg / w> 0.5 (4)
(Where d is the depth of the pre-groove, w is the opening width of the pre-groove, tg is the film thickness of the recording layer in the groove portion, tl is the film thickness of the recording layer in the land portion, h is the groove portion and The surface step of the recording layer formed in the land portion, wg represents the surface layer width of the recording layer in the groove opening)
[0013]
The material of the substrate used in the optical recording medium of the present invention may be basically transparent as long as it has a wavelength of 620 to 690 nm assumed for recording and reproduction. For example, organic polymer materials such as acrylic resin, polyethylene resin, polycarbonate resin, polystyrene resin, polyolefin resin, and epoxy resin, and inorganic materials such as glass are used. Of these, acrylic resin, polycarbonate resin, and polyolefin resin injection-molded substrates are preferred from the viewpoints of mechanical properties of substrates, ease of molding of grooves, pre-pits, etc., and economical use, especially for general use with CDs and the like. A proven polycarbonate resin substrate is more preferred.
[0014]
In addition, the shape of these transparent substrates may be a plate shape or a film shape, and may be a circle or a card. In consideration of DVD compatibility, it is desirable that the disk has a diameter of 80 mm or 120 mm and a center hole of about 15 mm is formed at the center. In general, submicron-order grooves and / or prepits are spirally or concentrically formed on the surface of these substrates. The grooves and pre-pits present on the substrate surface are preferably applied at the time of forming the substrate, but can also be applied by providing a thermosetting resin or ultraviolet curable resin layer on the substrate.
[0015]
Here, the groove shape, particularly the groove depth, not only dominates the servo stability as a tracking guide groove, but also directly or indirectly affects the film formation shape of the recording film formed thereon. As a result, the influence on the recording characteristics cannot be ignored. When maintaining stable tracking performance and considering the balance with the recording layer film thickness configuration described later, the optimum substrate groove depth d is in the range of 100 nm to 300 nm, preferably 120 nm to 200 nm.
Here, when d> 300 nm, it is difficult to transfer the groove to the substrate in manufacturing, and when d <100 nm, the recording film is difficult to seal inside the substrate groove, and it is difficult to maintain good performance.
[0016]
In the optical recording medium of the present invention, the shape of the recording film to be formed is particularly important. That is, regarding the shape of the recording film, in order to improve the pit edge particularly when recording at a higher density than CD, it is structurally very difficult to locally seal the recording layer only on the substrate groove. is important.
FIG. 2 shows a sectional view of the film formation shape in the optical recording medium of the present invention.
The recording layer is formed by forming the film thickness (tg) of the recording layer in the groove portion to be smaller than the pre-groove depth (d) of the substrate,
In addition, the surface step (h) of the recording layer formed in the groove part and the land part is formed largely with reference to the pre-groove depth (d).
In addition, the surface layer width (wg) at the portion of the formed recording layer is as large as possible with respect to the pre-groove opening width (w), and the protrusion of the recording layer from the groove to the land portion is small. Indispensable for improving the recording pit edge.
Furthermore, the reduction in the recording layer film thickness (tl) in the land portion accelerates heat propagation to the reflection layer via the recording layer surface layer interface, and reduces thermal interference between adjacent tracks. This is a necessary condition for sealing the density recording pits.
[0017]
The inventors changed the pre-groove conditions and recording layer film forming conditions of the substrate to be used (in the case of a coating method, rotation conditions, solvent conditions, environmental conditions (temperature, etc.), vapor deposition method, etc.), and the above d, h As a result of quantitative examination while variously changing t, tg, tl, and wg, a film structure that simultaneously satisfies the following equations (1) to (4) can be used to reproduce a shortest pit that is good for high-density recording. I found that it can be obtained well.
h / d> 0.3 (1)
tg ≦ d (2)
tl <100nm (3)
wg / w> 0.5 (4)
[0018]
In the optical recording medium of the present invention, control of tg ≦ d is particularly important. More preferably, the film formation structure is h / d> 0.4 and tl <60 nm.
In the film formation structure with tg> d and h / d ≦ 0.3, pit interference (crosstalk) between tracks becomes obvious, and the shortest pit jitter at the time of high-density recording tends to be greatly deteriorated. The film thickness tl ≧ 100 nm at the portion is not preferable because crosstalk between tracks cannot be ignored. Similarly, when wg / w ≦ 0.5, there is a tendency that the crosstalk is increased and the signal is deteriorated.
Here, the surface (interface) shapes of the substrate and the recording layer can be measured by STM or AFM. In addition, the film thickness of the dye can be measured from a cross-sectional SEM image of a frozen fracture surface of a film formation substrate sample in liquid nitrogen as a recording layer cross-sectional shape after film formation. Of course, dektack level difference data can also be quantified.
[0019]
The dye used for the recording layer in the optical recording medium of the present invention has an appropriate absorption in the focused laser wavelength range of 620 nm to 690 nm, and is irradiated with laser light having a certain energy or more accompanied by light / heat conversion. Basically, any organic dye material may be used as long as it is accompanied by physical / chemical deformation, alteration, and decomposition. When assuming high-density recording on the premise of reproduction compatibility with a DVD player, the optical characteristics of the dye material, that is, λmax exists in the vicinity of 550 nm to 600 nm, and the refractive index n in the assumed laser wavelength range is large. In order to obtain a high reflectivity and a high degree of modulation, it is desirable that (n ≧ 1.9) and the absorption is appropriate (attenuation constant k ≦ 0.25). Here, when n <1.9, the reflectivity is lowered, causing a problem in compatibility with a DVD player. When k> 0.25, the reflectivity is extremely lowered, and damage due to reproduction light is also caused. It is not preferable because it becomes apparent.
[0020]
From the viewpoint of thermal characteristics, both the melting point and the decomposition point of the dye material are 200 ° C. or more, which is essential for forming stable high density recording pits. As such specific dyes, cyanine, azo, phthalocyanine, porphyrin, dibenzofuran, indigo, and the like have been proposed. In the present invention, a metal complex of a monoazo compound represented by the following general formula (I) (Chemical Formula 3) is particularly preferable from the viewpoint of good optical characteristics, thermal characteristics, and durability performance.
[0021]
[Chemical 3]

(Wherein A is a residue that, together with the nitrogen and carbon atoms to which it is attached, forms a heterocycle that may be substituted with an electron donating or electron withdrawing group, and B is a bond to which Represents a residue which forms an aromatic ring which may be substituted with an electron donating group together with two carbon atoms in which X represents -OH group or -COOH group)
[0022]
In the metal complex of the monoazo compound represented by the general formula (I), examples of the residue forming the heterocyclic ring represented by A include a thiazole ring, a benzothiazole ring, a pyridobenzothiazole ring, and a benzopyridothiazole. Ring, pyridothiazole ring, pyridine ring, quinoline ring, thiadiazole ring, imidazole ring and the like. In particular, from the viewpoint of optical properties and solubility, a pyridine ring or a thiadiazole ring is preferable, and a pyridine ring is particularly excellent.
These heterocycles may be substituted with one or more electron-withdrawing groups and / or electron-donating groups, and further substituents for the purpose of controlling solubility and associating properties. Specific examples of these substituents include a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group, an aryl group, and a halogen atom. Of course, these substituents may further have a substituent.
[0023]
Examples of the residue that forms the aromatic ring represented by B in the general formula (I) include a benzene ring, a naphthalene ring, a pyridone ring, a pyridine ring, and a pyrazole ring. It is preferably a benzene ring, and is preferably modified with at least one electron donating group and / or a substituent for the purpose of controlling solubility and association. Examples of such a substituent include an alkyl group having 1 to 10 carbon atoms, an alkoxy group, and an amino group. These substituents may further have a substituent.
X in the general formula (I) is not particularly limited as long as it is a group having active hydrogen, but is preferably an —OH group or —COOH group.
[0024]
Furthermore, the metal to be coordinated is not particularly limited as long as it has a capability of forming a complex with an azo compound. From the viewpoint of stability and optical characteristics, transition metals such as Ni, Co, Fe, Mn, Pd, Cu, and Zn are preferable. Ni, Co, and Cu are particularly good. These azo metal complex compounds may be used alone or as a mixture of a plurality of compounds. The azo-based metal complex used in the present invention can be synthesized, for example, according to the method described in Furukawa; Analytica Chimica Acta 140 (1982) 281-289.
[0025]
Further, additives such as a resin, a leveling material, a quencher, a dye thermal decomposition accelerator, and an ultraviolet absorber can be mixed or introduced as a substituent in the recording layer as necessary. Of course, the organic dye of the present invention may be used alone or in combination of two or more.
[0026]
Next, a method for manufacturing the optical recording medium of the present invention will be described.
In the optical recording medium of the present invention, the method for forming the recording layer is not particularly limited, and includes a coating method such as a spin coating method and a casting method, a spray method, a sputtering method, a chemical vapor deposition method, and a vacuum vapor deposition method. The film is formed by applying the optimization conditions.
The point of the optical recording medium of the present invention is that the recording layer is hermetically sealed in the pre-groove of the substrate, and film formation control during the production is extremely important.
[0027]
Essentially, it is essential to achieve film formation (h / d: large, wg / w: large) following the groove shape, and groove film thickness (tg) <groove depth (d) by condition control. Vapor deposition and sputtering are essentially preferred. However, the land film thickness (tl) cannot be selectively made small, and in addition, precise management of the film thickness is substantially difficult by the vapor deposition method, and the dye is decomposed during the film formation process by the sputtering method. Therefore, precise control of conditions is required, and as a result, there is a difficulty that does not take on reality.
As a result of studying the film forming process by the spin coating method, which is an easy production method, the present inventors mainly optimize the solvent, coating rotation conditions, coating environment conditions (temperature, air volume, etc.), etc. It was found that the film formation shape can be sufficiently controlled by satisfying the condition of tg ≦ d.
[0028]
In the film formation shape control on the substrate groove in the coating method, the selection of the coating solvent and the solution concentration (viscosity) is very important. It is essential that the solvent dissolves or disperses the dye and does not damage the substrate. Further, in order to satisfy the conditions (1) to (4) described above, the evaporation of the coating solvent is necessary. Speed control is particularly important and has a great effect. According to the detailed study by the present inventors, the coating solvent is preferably one having a boiling point of 70 ° C to 150 ° C, more preferably 80 ° C to 120 ° C. For example, thinning the film thickness (tl) of the recording layer in the land portion can be easily achieved by selecting a solvent system having a low viscosity and slow evaporation, while the surface level difference between the groove layer and the recording layer in the land portion ( In order to increase h), it is preferable to apply a high viscosity solvent because the evaporation rate is high.
Here, balancing of both can be controlled by applying a mixed solvent, adjusting the dye dissolution concentration, controlling the evaporation rate by giving a gradient to the rotation conditions, adjusting the environmental temperature, and the like. The coating temperature is preferably 20 to 30 ° C, and the drying temperature is preferably about 50 to 100 ° C.
[0029]
Coating solvents include hydrocarbon solvents (hexane, cyclohexane, octane, toluene, xylene, etc.), alcohol solvents (methanol, ethanol, propanol, isopropanol, etc.), halogenated alcohol solvents (2, 2, 3, 3- Tetrafluoro-1-propanol, heptafluorobutanol, pentafluoropropanol, hexafluoroisopropanol, etc.), halogenated hydrocarbon solvents (chloroform, carbon tetrachloride, dichlorodifluoroethane, etc.), ether solvents, cellosolve solvents, etc. Is mentioned. These are used singly or in combination, considering the boiling point, vapor pressure, viscosity and the like.
In particular, in the case of coating a metal complex of a monoazo compound, a mixed system of an alcohol solvent and a halogenated alcohol solvent is effective.
[0030]
In the optical recording medium of the present invention, the formed recording layer can be laminated in two layers via an intermediate layer, and for the purpose of obtaining the enhancement effect of the reflective layer and the purpose of improving the recording characteristics, In some cases, an inorganic dielectric layer, a dye layer, or the like is laminated as an intermediate layer at the interface between the layer and the reflective layer.
[0031]
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, Cr, alone or in an alloy is used. It is possible to use. Of these, Au, Al, Ag, and Cu are optimal because of their high reflectivity.
Examples of the method for producing the reflective layer include a sputtering method, a chemical vapor deposition method, a vacuum vapor deposition method, and an imprinting method, and the film is usually formed to a film thickness of 30 to 200 nm. Preferably it is 50-150 nm. In some cases, an adhesive layer is provided between the recording layer and the reflective layer for the purpose of improving the adhesion of the reflective layer.
[0032]
In the optical recording medium of the present invention, in order to protect the recording layer and the reflective layer, a protective layer that is a regular method may be provided on the reflective layer by a known technique, or two substrates may be bonded together.
The material of the protective layer is not particularly limited as long as it protects the recording layer and the reflective layer from external force. Examples of the organic substance include a thermoplastic resin, a thermosetting resin, and a UV curable resin. Of these, UV curable resins are preferred.
As a method for forming the protective layer, a coating method such as a spin coating method or a casting method is applied as in the recording layer.
In the optical recording medium of the present invention, a label or the like can be further printed on the protective layer. Further, an ultraviolet curable resin or an inorganic thin film may be formed on the mirror surface side of the substrate in order to protect the surface and prevent the adhesion of dust and the like.
[0033]
As a method for recording information on the optical recording medium of the present invention, for example, while rotating the optical recording medium at a constant linear velocity, the bottom of the guide groove is irradiated on the bottom of the guide groove while rotating the optical recording medium on the guide groove. This is done by forming pits for reproduction on the recording layer. As the signal, it is preferable to evaluate the effect of the present invention by recording the same EFM + signal as the DVD and quantifying the pit edge fluctuation with respect to the channel bit clock at that time as jitter.
[0034]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, the aspect of this invention is not limited to this.
Example 1
On the surface having the groove of an injection molded polycarbonate substrate having a thickness of 0.6 mm and a diameter of 120 mm having a spiral groove (depth 140 mm, width 0.35 μm, pitch 0.74 μm), the following formula (II) In a (9: 1) mixed solvent of 2,2,3,3-tetrafluoro-1-propanol (boiling point 110 ° C.) and isopropyl alcohol (boiling point 80 ° C.), A solution of 20 g / l was obtained. Spin coating was performed with a gradient of 9 seconds from a rotational speed of 300 rpm to 3000 rpm, and a recording layer consisting essentially of a dye was formed on the groove and dried in an oven at 70 ° C. for 2 hours.
[0035]
[Formula 4]

The film thickness (tg) of the recording layer in the groove part, the film thickness (tl) of the recording layer in the land part, and the surface step (h) between the recording layer in the groove part and the land part. As a result of measuring with a cross-sectional SEM, they were measured as tg = 100 nm, tl = 50 nm, h = 90 nm, and wg = 0.22 μm, respectively.
Since d = 140 nm and w = 0.35 μm, h / d = 0.64 and wg / w = 0.63.
[0036]
Next, Au was sputtered on the recording layer using a Balzers sputtering apparatus (CDI-900) to form a reflective layer having a thickness of 80 nm. Further, a UV curable resin SD-17 (Dainippon Ink Chemical Co., Ltd.) was spin-coated on the reflective layer, and then irradiated with UV to form a protective layer having a thickness of 3 μm. A UV curable resin SD-301 (Dainippon Ink Chemical Co., Ltd.) is applied on top of this, and the same 0.6 mm substrate as above is overlaid on this adhesive and rotated at a high speed to remove excess adhesive. After that, an optical recording medium was prepared by applying UV light and bonding.
[0037]
This optical recording medium is placed on a turntable and rotated at a linear velocity of 3.7 m / s, and equipped with a laser having a wavelength = 639 nm and an optical head having an NA = 0.60. 1000) EFM + modulation signal with the shortest pit length of 0.40 μm was recorded while continuously changing the recording power using an EFM + encoder manufactured by KENWOOD, and the laser output was set to 0.5 mW using the same device. The recording signal was read out. Note that ecologicalization processing in accordance with the DVD playback standard was performed during signal playback. As a result, the jitter was 8.1% of the channel bit clock. This medium could be satisfactorily reproduced by, for example, a Matsushita Electric Industrial DVD player (DVD-A300).
[0038]
Example 2
A recording medium was produced in the same manner as in Example 1 except that a 1: 2 mixed solvent of pentafluoropropanol and octafluoropentanol was used as a coating solvent.
As a result of measuring the shape of the recording layer, tg = 80 nm, tl = 60 nm, h = 120 nm, and wg = 0.25 μm. Therefore, h / d = 0.86, wg / w = 0.71, and the jitter was as good as 7.7%.
[0039]
Example 3
A recording medium was produced in the same manner as in Example 1 except that a polycarbonate substrate having a groove with a depth d = 180 nm and an opening width w = 0.35 μm was used, and signal evaluation was performed.
The shape of the recording layer was tg = 120 nm, tl = 30 nm, h = 90 nm, wg = 0.28 μm (h / d = 0.50, wg / w = 0.80). The jitter in this system was 7.2%.
[0040]
Example 4
A recording medium was prepared according to the same formulation as Example 1 except that a monoazo compound Ni complex represented by the following formula (III) (Chemical Formula 5) was used, and signal evaluation was performed.
The shape of the recording layer was the same as in Example 1, and the jitter value at this time was 8.9%.
[0041]
[Chemical formula 5]

[0042]
Comparative Example 1
A recording medium was produced in the same manner as in Example 1 except that the coating rotation conditions were 800 rpm and 15 seconds, and signal evaluation was performed.
The shape of the recording layer was tg = 180 nm, tl = 100 nm, h = 60 nm (h / d = 0.43). Since tg> d, wg = 0 and wg / w = 0. At this time, the jitter was 16.5%, which was greatly deteriorated. The crosstalk was also very large at 51%.
This medium could not be reproduced by the above-mentioned Matsushita DVD player.
[0043]
Comparative Example 2
A recording medium was produced in the same manner as in Example 1 except that a polycarbonate substrate having a groove with a depth d = 50 nm was used, and signal evaluation was performed.
tg = 90 nm, tl = 55 nm, h = 15 nm (h / d = 0.3). At this time, the jitter was 15.8%. Also, tracking was very difficult to control.
[0044]
Comparative Example 3
Example except that (2: 1) solvent of 2,2,3,3-tetrafluoro-1-propanol and ethylene glycol was used as a coating solvent, a 10 g / l solution was prepared, and the coating rotation condition was 800 rpm. In the same manner as in Example 1, a recording medium was prepared and evaluated. The shape was tg = 100 nm, tl = 60 nm, h = 100 nm, wg = 0.10 μm (h / d = 0.71, wg / w = 0.29), and the jitter level was 18.1%. .
[0045]
Comparative Example 4
A recording medium was prepared in the same manner as in Example 1 except that a cyanine dye represented by the following formula (IV) (Chemical Formula 6) was used, and signal evaluation was performed.
The shape is tg = 110 nm, tl = 40 nm, h = 70 nm, wg = 0.25 μm (h / d = 0.5, wg / w = 0.71), and the jitter level is very high at 20.1%. It was inferior.
[0046]
[Chemical 6]

Table 1 (Table 1) collectively shows the results obtained by forming the recording medium by changing the groove depth of the substrate, the coating solvent, and the coating rotation conditions.
[0047]
[Table 1]

[0048]
【The invention's effect】
In an optical recording medium having at least a recording layer and a reflective layer on a transparent substrate having a groove, a recording layer containing a dye is applied to a substrate having a pre-groove having a depth d and an opening width w under specific conditions. By forming the film so as to satisfy the requirements, it was possible to provide a recording medium having a higher density than the CD using a laser beam of 620 nm to 690 nm.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an optical recording medium of the present invention.
FIG. 2 is a sectional view of a film forming shape of an optical recording medium of the present invention
[Explanation of symbols]
1: Substrate
2: Recording layer
3: Reflective layer
4: Protective layer

Claims (2)

In an optical recording medium having at least a recording layer and a reflective layer on a transparent substrate having grooves, a metal complex of a monoazo compound represented by the following general formula (I) (Chemical formula 1) on the substrate having pre-grooves And a recording layer containing the same, and the recording layer satisfies the following formulas (1) to (4) at the same time. Type optical recording medium.
h / d> 0.3 (1)
tg ≦ d (2)
tl <100nm (3)
wg / w> 0.5 (4)
(Where d is the depth of the pre-groove, w is the opening width of the pre-groove, tg is the film thickness of the recording layer in the groove portion, tl is the film thickness of the recording layer in the land portion, h is the groove portion and The surface step of the recording layer formed in the land portion, wg represents the surface layer width of the recording layer in the groove opening)

(In the formula (I), A represents a residue which forms a heterocyclic ring which may be substituted with an electron donating group or an electron withdrawing group together with a nitrogen atom and a carbon atom to which it is bonded; Represents a residue which together with the two carbon atoms to which it is attached forms an aromatic ring which may be substituted with an electron donating group, X represents an —OH group or a —COOH group)   2. The method of manufacturing an optical recording medium according to claim 1, wherein the recording layer is formed by a coating method.

Images