JP2005071396A - Method for recording optical recording medium and recording device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optimal recording method for forming the signal of a satisfactory signal characteristic in each recording layer in an optical recording medium provided with a plurality of recording layers where information can be recorded by irradiating them with laser light from one surface side. <P>SOLUTION: In the recording method of an optical recording medium for forming a mark of a length nT (n is a natural number of 4 to 14, and T is a reference clock frequency) as an information signal to the plurality of recording layers by irradiating them with recording lasers from one surface side, when forming the mark of the length nT by irradiating them with recording lasers in a shape of a pulse using a first pulse for forming at least the beginning area of the mark, and a last pulse for forming the ending area of the mark, the mark is formed by varying the front edge of the first pulse and/or the rear edge of the last pulse according to the mark length. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３３】
（環Ａ^１及びＡ^２は、各々独立に置換基を有していてもよい含窒素芳香族複素環であり、環Ｂ^１及びＢ^２は、各々独立に置換基を有していてもよい芳香族環である。Ｘは、少なくとも２個のフッ素原子で置換されている炭素数１〜６のアルキル基である。）で表される化合物が好ましい。
本光記録媒体の記録層（なお、以下「記録層」という場合には、特にことわり書きのない限り、第１の記録層１と第２の記録層２とをともに指すものとする。）に使用される有機色素は、３５０〜９００ｎｍ程度の可視光〜近赤外域に最大吸収波長λｍａｘを有し、青色〜近マイクロ波レーザでの記録に適する色素化合物が好ましい。通常ＣＤ−Ｒに用いられるような波長７７０〜８３０ｎｍ程度の近赤外レーザ（代表的には７８０ｎｍ，８３０ｎｍなど）や、ＤＶＤ−Ｒに用いられるような波長６２０〜６９０ｎｍ程度の赤色レーザ（代表的には６３５ｎｍ，６５０ｎｍ，６８０ｎｍなど）、あるいは波長４１０ｎｍや５１５ｎｍなどのいわゆるブルーレーザなどでの記録に適する色素がより好ましい。
【００３４】
色素は一種でもよいし、同じ種類のものや異なる種類のものを二種以上混合して用いても良い。さらに、上記複数の波長の記録光に対し、各々での記録に適する色素を併用して、複数の波長域でのレーザ光による記録に対応する光記録媒体とすることもできる。
また、記録層は、記録層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。
【００３５】
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。
【００３６】
さらに、本光記録媒体の記録層には、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。
【００３７】
記録層の膜厚は、記録方法などにより適した膜厚が異なるため、特に限定するものではないが、十分な変調度を得るためには通常５ｎｍ以上が好ましく、より好ましくは１０ｎｍ以上であり、特に好ましくは２０ｎｍ以上である。但し、本光記録媒体においては適度に光を透過させるためには厚すぎない必要があるため、通常３μｍ以下であり、好ましくは１μｍ以下、より好ましくは２００ｎｍ以下である。記録層の膜厚は通常、溝部とランド部で異なるが、本光記録媒体において記録層の膜厚は基板の溝部における膜厚を言う。
【００３８】
記録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が、量産性、コスト面からはスピンコート法が好ましい。また厚みの均一な記録層が得られるという点からは、塗布法より真空蒸着法の方が好ましい。
【００３９】
スピンコート法による成膜の場合、回転数は１０〜１５０００ｒｐｍが好ましく、スピンコートの後、加熱あるいは溶媒蒸気にあ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、２−ヒドロキシ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。
【００４０】
真空蒸着法の場合は、例えば有機色素と、必要に応じて各種添加剤等の記録層成分を、真空容器内に設置されたるつぼに入れ、真空容器内を適当な真空ポンプで１０^−２〜１０^−５Ｐａ程度にまで排気した後、るつぼを加熱して記録層成分を蒸発させ、るつぼと向き合って置かれた基板上に蒸着させることにより、記録層を形成する。
（ｃ）第１反射層３について
第１反射層３は、ある程度の光透過率を持つ反射層である。つまり、記録再生光の吸収が小さく、光透過率が４０％以上あり、かつ適度な光反射率（通常、３０％以上）を持つ反射層である。なお、第１反射層３を半透明反射層３ともいう。例えば、反射率の高い金属を薄く設けることにより適度な透過率を持たせることができる。また、ある程度の耐食性があることが望ましい。更に、第１反射層３の上層（ここでは中間樹脂層４）の浸み出しにより第１記録層２が影響されないよう遮断性を持つことが望ましい。
【００４１】
高透過率を確保するために、第１反射層３の厚さは通常、５０ｎｍ以下が好適である。より好適には３０ｎｍ以下である。更に好ましくは２５ｎｍ以下である。但し、第１記録層２が第１反射層３の上層により影響されないために、ある程度の厚さが必要であり、通常３ｎｍ以上とする。より好ましくは５ｎｍ以上とする。
【００４２】
第１反射層３の材料としては、再生光の波長で反射率が適度に高いもの、例えば、Ａｕ、Ａｌ、Ａｇ、Ｃｕ、Ｔｉ、Ｃｒ、Ｎｉ、Ｐｔ、Ｔａ、Ｐｄ、Ｍｇ、Ｓｅ、Ｈｆ、Ｖ、Ｎｂ、Ｒｕ、Ｗ、Ｍｎ、Ｒｅ、Ｆｅ、Ｃｏ、Ｒｈ、Ｉｒ、Ｚｎ、Ｃｄ、Ｇａ、Ｉｎ、Ｓｉ、Ｇｅ、Ｔｅ、Ｐｂ、Ｐｏ、Ｓｎ、Ｂｉ及び希土類金属などの金属及び半金属を単独あるいは合金にして用いることが可能である。この中でもＡｕ、Ａｌ、Ａｇは反射率が高く第１反射層３の材料として適している。これらを主成分とする以外に他成分を含んでいても良い。
【００４３】
なかでもＡｇを主成分としているものはコストが安い点、反射率が高い点から特に好ましい。ここで主成分とは含有率が５０％以上のものをいう。
第１反射層３は膜厚が薄く、膜の結晶粒が大きいと再生ノイズの原因となるため、結晶粒が小さい材料を用いるのが好ましい。純銀は結晶粒が大きい傾向があるためＡｇは合金として用いるのが好ましい。
【００４４】
中でもＡｇを主成分とし、Ｔｉ、Ｚｎ、Ｃｕ、Ｐｄ、Ａｕ及び希土類金属よりなる群から選ばれる少なくとも１種の元素を０．１〜１５原子％含有することが好ましい。Ｔｉ、Ｚｎ、Ｃｕ、Ｐｄ、Ａｕ及び希土類金属のうち２種以上含む場合は、各々０．１〜１５原子％でもかまわないが、それらの合計が０．１〜１５原子％であることが好ましい。
【００４５】
特に好ましい合金組成は、Ａｇを主成分とし、Ｔｉ、Ｚｎ、Ｃｕ、Ｐｄ、Ａｕよりなる群から選ばれる少なくとも１種の元素を０．１〜１５原子％含有し、かつ少なくとも１種の希土類元素を０．１〜１５原子％含有するものである。希土類金属の中では、ネオジウムが特に好ましい。具体的には、ＡｇＰｄＣｕ、ＡｇＣｕＡｕ、ＡｇＣｕＡｕＮｄ、ＡｇＣｕＮｄなどである。
【００４６】
第１反射層３としてはＡｕのみからなる層は結晶粒が小さく、耐食性に優れ好適である。ただし、Ａｇ合金に比べて高価である。
また、第１反射層３としてＳｉからなる層を用いることも可能である。
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。
【００４７】
第１反射層３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、第１基板１と第１記録層２との間、及び／又は、第１記録層２と第１反射層３との間に、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または有機系の中間層、接着層を設けることもできる。
（ｄ）中間樹脂層４について
中間樹脂層４は、透明である必要があるほか、凹凸により溝やピットが形成可能である必要がある。また接着力が高く、硬化接着時の収縮率が小さいと媒体の形状安定性が高く好ましい。
【００４８】
中間樹脂層４の屈折率（記録光又は再生光の波長に対する屈折率）は、通常１．４０以上であり、好ましくは１．４５以上である。但し、通常１．７０以下であり、好ましくは１．６５以下である。
そして、中間樹脂層４は、第２記録層５にダメージを与えない材料からなることが望ましい。但し、中間樹脂層４は通常、樹脂からなるため第２記録層５と相溶しやすく、これを防ぎダメージを抑えるために両層の間に後述のバッファー層を設けることが望ましい。
【００４９】
さらに、中間樹脂層４は、第１反射層３にダメージを与えない材料からなることが望ましい。但し、ダメージを抑えるために両層の間に後述のバッファー層を設けることもできる。
本光記録媒体において、中間樹脂層４の膜厚は正確に制御することが好ましい。中間樹脂層４の膜厚は、通常５μｍ以上が好ましい。２層の記録層に別々にフォーカスサーボをかけるためには両記録層の間にある程度の距離がある必要がある。フォーカスサーボ機構にもよるが、通常５μｍ以上、好ましくは１０μｍ以上が必要である。
【００５０】
一般に、対物レンズの開口数が高いほどその距離は小さくてよい傾向がある。但しあまり厚いと２層の記録層にフォーカスサーボを合わせるのに時間を要し、また対物レンズの移動距離も長くなるため好ましくない。また硬化に時間を要し生産性が低下するなどの問題があるため、通常、１００μｍ以下が好ましい。
中間樹脂層４には凹凸が螺旋状又は同心円状に設けられ、溝及びランドを形成する。通常、このような溝及び／又はランドを記録トラックとして、第２記録層５に情報が記録・再生される。通常、第２記録層５は塗布形成されるので溝部で厚膜となり記録再生に適する。通常、溝幅は２００〜５００ｎｍ程度であり、溝深さは１２０〜２５０ｎｍ程度である。また記録トラックが螺旋状である場合、トラックピッチは０．１〜２．０μｍ程度であることが好ましい。
【００５１】
このような凹凸は、コストの観点から、凹凸を持つ樹脂スタンパ等から光硬化性樹脂などの硬化性樹脂に転写、硬化させて製造するのが好ましい。以下、このような方法を２Ｐ法（Ｐｈｏｔｏ Ｐｏｌｙｍｅｒｉｚａｔｉｏｎ法）と称することがある。
中間樹脂層４の材料としては、例えば、熱可塑性樹脂、熱硬化性樹脂、電子線硬化性樹脂、紫外線硬化性樹脂（遅延硬化型を含む）等を挙げることができる。
【００５２】
熱可塑性樹脂、熱硬化性樹脂などは適当な溶剤に溶解して塗布液を調製し、これを塗布し、乾燥（加熱）することによって形成することができる。紫外線硬化性樹脂は、そのままもしくは適当な溶剤に溶解して塗布液を調製した後にこの塗布液を塗布し、紫外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。紫外線硬化性樹脂には様々な種類があり、透明であればいずれも用いうる。またそれらの材料を単独であるいは混合して用いても良いし、１層だけではなく多層膜にして用いても良い。
【００５３】
塗布方法としては、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等の方法が用いられるが、この中でもスピンコート法が好ましい。或いは、粘度の高い樹脂はスクリーン印刷等によっても塗布形成できる。紫外線硬化性樹脂は、生産性を２０〜４０℃において液状であるものを用いると、溶媒を用いることなく塗布でき好ましい。また、粘度は２０〜１０００ｍＰａ・ｓとなるように調製するのが好ましい。
【００５４】
さて、紫外線硬化性接着剤としては、ラジカル系紫外線硬化性接着剤とカチオン系紫外線硬化性接着剤があるが、いずれも使用可能である。
ラジカル系紫外線硬化性接着剤としては、公知の全ての組成物を用いることができ、紫外線硬化性化合物と光重合開始剤を必須成分として含む組成物が用いられる。紫外線硬化性化合物としては、単官能（メタ）アクリレートや多官能（メタ）アクリレートを重合性モノマー成分として用いることができる。これらは、各々、単独または２種類以上併用して用いることができる。ここで、本発明では、アクリレートとメタアクリレートとを併せて（メタ）アクリレートと称する。
【００５５】
本光記録媒体に使用できる重合性モノマーとしては例えば以下のものが挙げられる。単官能（メタ）アクリレートとしては例えば、置換基としてメチル、エチル、プロピル、ブチル、アミル、２−エチルヘキシル、オクチル、ノニル、ドデシル、ヘキサデシル、オクタデシル、シクロヘキシル、ベンジル、メトキシエチル、ブトキシエチル、フェノキシエチル、ノニルフェノキシエチル、テトラヒドロフルフリル、グリシジル、２−ヒドロキシエチル、２−ヒドロキシプロピル、３−クロロ−２−ヒドロキシプロピル、ジメチルアミノエチル、ジエチルアミノエチル、ノニルフェノキシエチルテトラヒドロフルフリル，カプロラクトン変性テトラヒドロフルフリル、イソボルニル，ジシクロペンタニル，ジシクロペンテニル，ジシクロペンテニロキシエチル等の如き基を有する（メタ）アクリレート等が挙げられる。
【００５６】
また、多官能（メタ）アクリレートとしては例えば、１，３−ブチレングリコール、１，４−ブタンジオール、１，５−ペンタンジオール、３−メチル−１，５−ペンタンジオール、１，６−ヘキサンジオール、ネオペンチルグリコール、１，８−オクタンジオール、１，９−ノナンジオール、トリシクロデカンジメタノール、エチレングリコール、ポリエチレングリコール、プロピレングリコール、ジプロピレングリコール、トリプロピレングリコール、ポリプロピレングリコール等のジ（メタ）アクリレート、トリス（２−ヒドロキシエチル）イソシアヌレートのジ（メタ）アクリレート、ネオペンチルグリコール１モルに４モル以上のエチレンオキサイドもしくはプロピレンオキサイドを付加して得たジオールのジ（メタ）アクリレート、ビスフェノールＡ１モルに２モルのエチレンオキサイドもしくはプロピレンオキサイドを付加して得たジオールのジ（メタ）アクリレート、トリメチロールプロパン１モルに３モル以上のエチレンオキサイドもしくはプロピレンオキサイドを付加して得たトリオールのジまたはトリ（メタ）アクリレート、ビスフェノールＡ１モルに４モル以上のエチレンオキサイドもしくはプロピレンオキサイドを付加して得たジオールのジ（メタ）アクリレート、トリメチロールプロパントリ（メタ）アクリレート、ペンタエリスリトールトリ（メタ）アクリレート、ジペンタエリスリトールのポリ（メタ）アクリレート、エチレンオキサイド変性リン酸（メタ）アクリレート、エチレンオキサイド変性アルキル化リン酸（メタ）アクリレート等が挙げられる。
【００５７】
また、重合性モノマーと同時に併用できるものとしては、重合性オリゴマーとしてポリエステル（メタ）アクリレート、ポリエーテル（メタ）アクリレート、エポキシ（メタ）アクリレート、ウレタン（メタ）アクリレート等がある。
更に、本光記録媒体に使用する光重合開始剤は、用いる重合性オリゴマーおよび／または重合性モノマーに代表される紫外線硬化性化合物が硬化できる公知のものがいずれも使用できる。光重合開始剤としては、分子開裂型または水素引き抜き型のものが本光記録媒体に好適である。
【００５８】
このような例としては、ベンゾインイソブチルエーテル、２，４−ジエチルチオキサントン、２−イソプロピルチオキサントン、ベンジル、２，４，６−トリメチルベンゾイルジフェニルフォスフィンオキシド、２−ベンジル−２−ジメチルアミノ−１−（４−モルフォリノフェニル）−ブタン−１−オン、ビス（２，６−ジメトキシベンゾイル）−２，４，４−トリメチルペンチルフォスフィンオキシド等が好適に用いられ、さらにこれら以外の分子開裂型のものとして、１−ヒドロキシシクロヘキシルフェニルケトン、ベンゾインエチルエーテル、ベンジルジメチルケタール、２−ヒドロキシ−２−メチル−１−フェニルプロパン−１−オン、１−（４−イソプロピルフェニル）−２−ヒドロキシ−２−メチルプロパン−１−オンおよび２−メチル−１−（４−メチルチオフェニル）−２−モルフォリノプロパン−１−オン等を併用しても良いし、さらに水素引き抜き型光重合開始剤である、ベンゾフェノン、４−フェニルベンゾフェノン、イソフタルフェノン、４−ベンゾイル−４’−メチル−ジフェニルスルフィド等も併用できる。
【００５９】
また光重合開始剤に対する増感剤として例えば、トリメチルアミン、メチルジメタノールアミン、トリエタノールアミン、ｐ−ジエチルアミノアセトフェノン、ｐ−ジメチルアミノ安息香酸エチル、ｐ−ジメチルアミノ安息香酸イソアミル、Ｎ，Ｎ−ジメチルベンジルアミンおよび４，４’−ビス（ジエチルアミノ）ベンゾフェノン等の、前述重合性成分と付加反応を起こさないアミン類を併用することもできる。もちろん、上記光重合開始剤や増感剤は、紫外線硬化性化合物への溶解性に優れ、紫外線透過性を阻害しないものを選択して用いることが好ましい。
【００６０】
また、カチオン系紫外線硬化性接着剤としては公知のすべての組成物を用いることができ、カチオン重合型の光開始剤を含むエポキシ樹脂がこれに該当する。カチオン重合型の光開始剤としては、スルホニウム塩、ヨードニウム塩およびジアゾニウム塩等がある。
ヨードニウム塩の１例を示すと以下の通りである。ジフェニルヨードニウム ヘキサフルオロホスフェート、ジフェニルヨードニウム ヘキサフルオロアンチモネート、ジフェニルヨードニウム テトラフルオロボレート、ジフェニルヨードニウム テトラキス（ペンタフルオロフェニル）ボレート、ビス（ドデシルフェニル）ヨードニウム ヘキサフルオロホスフェート、ビス（ドデシルフェニル）ヨードニウム ヘキサフルオロアンチモネート、ビス（ドデシルフェニル）ヨードニウム テトラフルオロボレート、ビス（ドデシルフェニル）ヨードニウムテトラキス（ペンタフルオロフェニル）ボレート、４−メチルフェニル−４−（１−メチルエチル）フェニルヨードニウム ヘキサフルオロホスフェート、４−メチルフェニル−４−（１−メチルエチル）フェニルヨードニウム ヘキサフルオロアンチモネート、４−メチルフェニル−４−（１−メチルエチル）フェニルヨードニウム テトラフルオロボレート、４−メチルフェニル−４−（１−メチルエチル）フェニルヨードニウム テトラキス（ペンタフルオロフェニル）ボレート、などが挙げられる。
【００６１】
エポキシ樹脂は、ビスフェノールＡ−エピクロールヒドリン型、脂環式エポキシ、長鎖脂肪族型、臭素化エポキシ樹脂、グリシジルエステル型、グリシジルエーテル型、複素環式系等種々のものがいずれであってもかまわない。
エポキシ樹脂としては、反射層にダメージを与えないよう、遊離したフリーの塩素および塩素イオン含有率が少ないものを用いるのが好ましい。塩素の量が１重量％以下が好ましく、より好ましくは０．５重量％以下である。
【００６２】
カチオン型紫外線硬化性樹脂１００重量部当たりのカチオン重合型光開始剤の割合は通常、０．１〜２０重量部であり、好ましくは０．２〜５重量部である。なお、紫外線光源の波長域の近紫外領域や可視領域の波長をより有効に利用するため、公知の光増感剤を併用することができる。この際の光増感剤としては、例えばアントラセン、フェノチアジン、ベンジルメチルケタール、ベンゾフェノン、アセトフェノン等が挙げられる。
【００６３】
また、紫外線硬化性接着剤には、必要に応じてさらにその他の添加剤として、熱重合禁止剤、ヒンダードフェノール、ヒンダードアミン、ホスファイト等に代表される酸化防止剤、可塑剤およびエポキシシラン、メルカプトシラン、（メタ）アクリルシラン等に代表されるシランカップリング剤等を、各種特性を改良する目的で配合することもできる。これらは、紫外線硬化性化合物への溶解性に優れたもの、紫外線透過性を阻害しないものを選択して用いる。
（ｅ）第２記録層５について
第２記録層５に用いる色素は、通常、片面型記録媒体（例えばＣＤ−Ｒ，ＤＶＤ−Ｒ，ＤＶＤ＋Ｒ）等に用いる色素よりも高感度である。本光記録媒体においては、入射した光ビームのパワーが第１記録層２や半透明反射層３の存在等で減少するため、約半分のパワーで記録するために、特に感度が高い必要があるのである。
【００６４】
また、良好な記録再生特性を実現するためには低発熱で高屈折率な色素であることが望ましい。
ここで、第２記録層５に用いる色素の屈折率（記録光又は再生光の波長に対する屈折率）は、通常１．００以上であり、好ましくは１．５０以上である。但し、通常３．００以下である。
【００６５】
また、第２記録層５に用いる色素の消衰係数（記録光又は再生光の波長に対する消衰係数）は、通常０．５０以下であり、好ましくは０．３０以下である。消衰係数が大きすぎると、色素記録層による吸収が大きくなりすぎ、反射率が低くなってしまう。但し、記録が行なわれるためにはある程度吸収があることが好ましく、下限は特に無いが、通常０．００１以上である。
【００６６】
更に、第２記録層５と反射層６との組合せにおいて、光の反射及び吸収を適切な範囲とすることが望ましい。記録感度を高くし、かつ記録時の熱干渉を小さくできる。
第２記録層５の材料、成膜方法等についてはほぼ第１記録層２と同様に説明されるため、異なる点のみ説明する。
【００６７】
第２記録層５の膜厚は、記録方法などにより適した膜厚が異なるため、特に限定するものではないが、十分な変調度を得るためには通常１０ｎｍ以上が好ましく、より好ましくは３０ｎｍ以上であり、特に好ましくは５０ｎｍ以上である。但し、適度な反射率を得るためには厚すぎない必要があるため、通常３μｍ以下であり、好ましくは１μｍ以下、より好ましくは２００ｎｍ以下である。ここで、第２記録層５の膜厚は、通常、厚膜部における膜厚をいう。
【００６８】
第１記録層２と第２記録層５とに用いる材料は同じでも良いし異なっていてもよい。
（ｆ）第２反射層６について
第２反射層６は、高反射率である必要がある。また、高耐久性であることが望ましい。
【００６９】
高反射率を確保するために、第２反射層６の厚さは通常、２０ｎｍ以上が好適である。より好適には３０ｎｍ以上である。更に好ましくは５０ｎｍ以上である。但し、生産のタクトタイムを短くし、コストを下げるためにはある程度薄いことが好ましく、通常４００ｎｍ以下とする。より好ましくは３００ｎｍ以下とする。
【００７０】
第２反射層６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及びＰｄの金属を単独あるいは合金にして用いることが可能である。この中でもＡｕ、Ａｌ、Ａｇは反射率が高く第２反射層６の材料として適している。これらを主成分とする以外に他成分として下記のものを含んでいても良い。他成分の例としては、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及び希土類金属などの金属及び半金属を挙げることができる。
【００７１】
中でもＡｇを主成分としているものはコストが安い点、高反射率が出やすい点、更に後で述べる印刷受容層を設ける場合には地色が白く美しいものが得られる点等から特に好ましい。ここで主成分とは含有率が５０％以上のものをいう。
第２反射層６は高耐久性（高耐食性）を確保するため、Ａｇは純銀よりも合金として用いるのが好ましい。
【００７２】
中でもＡｇを主成分とし、Ｔｉ、Ｚｎ、Ｃｕ、Ｐｄ、Ａｕ及び希土類金属よりなる群から選ばれる少なくとも１種の元素を０．１〜１５原子％含有することが好ましい。Ｔｉ、Ｚｎ、Ｃｕ、Ｐｄ、Ａｕ及び希土類金属のうち２種以上含む場合は、各々０．１〜１５原子％でもかまわないが、それらの合計が０．１〜１５原子％であることが好ましい。
【００７３】
特に好ましい合金組成は、Ａｇを主成分とし、Ｔｉ、Ｚｎ、Ｃｕ、Ｐｄ、Ａｕよりなる群から選ばれる少なくとも１種の元素を０．１〜１５原子％含有し、かつ少なくとも１種の希土類元素を０．１〜１５原子％含有するものである。希土類金属の中では、ネオジウムが特に好ましい。具体的には、ＡｇＰｄＣｕ、ＡｇＣｕＡｕ、ＡｇＣｕＡｕＮｄ、ＡｇＣｕＮｄなどである。
【００７４】
第２反射層６としてはＡｕのみからなる層は高耐久性（高耐食性）が高く好適である。ただし、Ａｇ合金に比べて高価である。
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、第２反射層６として用いることも可能である。
第２反射層６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、第２反射層６の上下に反射率の向上、記録特性の改善、密着性の向上等のために公知の無機系または有機系の中間層、接着層を設けることもできる。
（ｇ）接着層７について
接着層７は、透明である必要はないが、接着力が高く、硬化接着時の収縮率が小さいと媒体の形状安定性が高く好ましい。
【００７５】
また、接着層７は第２反射層６にダメージを与えない材料からなることが望ましい。但し、ダメージを抑えるために両層の間に公知の無機系または有機系の保護層を設けることもできる。
本光記録媒体において、接着層７の膜厚は、通常２μｍ以上が好ましい。所定の接着力を得るためにはある程度の膜厚が必要である。より好ましくは５μｍ以上である。但し光記録媒体をできるだけ薄くするために、また硬化に時間を要し生産性が低下するなどの問題があるため、通常、１００μｍ以下が好ましい。
【００７６】
接着層７の材料は、中間樹脂層４の材料と同様のものが用いうるほか、感圧式両面テープ等も使用可能である。感圧式両面テープを反射層６と第２基板８との間に挟んで押圧することにより、接着層７を形成できる。
（ｈ）第２基板８について
第２基板８は、光記録媒体がある程度の剛性を有するよう、形状安定性を備えるのが望ましい。即ち機械的安定性が高く、剛性が大きいことが好ましい。また接着層７との接着性が高いことが望ましい。
【００７７】
上述のように第１基板１が十分な形状安定性を備えていない場合は、第２基板８は特に形状安定性が高い必要がある。この点で吸湿性が小さいことが望ましい。但し第２基板８は透明である必要はない。また第２基板８は鏡面基板で良く、凹凸を形成する必要はないので射出成形による転写性は必ずしも良い必要はない。
【００７８】
このような材料としては、第１基板１に用いうる材料と同じものが用い得るほか、例えば、Ａｌを主成分とした例えばＡｌ−Ｍｇ合金等のＡｌ合金基板や、Ｍｇを主成分とした例えばＭｇ−Ｚｎ合金等のＭｇ合金基板、シリコン、チタン、セラミックスのいずれかからなる基板やそれらを組み合わせた基板などを用いることができる。
【００７９】
なお、成形性などの高生産性、コスト、低吸湿性、形状安定性などの点からはポリカーボネートが好ましい。耐薬品性、低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、高速応答性などの点からは、ガラス基板が好ましい。
光記録媒体に十分な剛性を持たせるために、第２基板８はある程度厚いことが好ましく、厚さは０．３ｍｍ以上が好ましい。但し薄いほうが記録再生装置の薄型化に有利であり、好ましくは３ｍｍ以下である。より好ましくは１．５ｍｍ以下である。
【００８０】
第２基板８は凹凸を持たない鏡面基板で良いが、生産しやすさの観点から、射出成型により製造するのが望ましい。
第１基板１と第２基板８の好ましい組合せの一例は、第１基板１と第２基板８とが同一材料からなり、厚さも同一である。剛性が同等でバランスが取れているので、環境変化に対しても媒体として変形しにくく好ましい。この場合、環境が変化したときの変形の程度や方向も両基板で同様であると好ましい。
【００８１】
他の好ましい組合せの一例は、第１基板１が０．１ｍｍ程度と薄く、第２基板８が１．１ｍｍ程度と厚いものである。対物レンズが記録層に近づきやすく記録密度を上げやすいため好ましい。このとき第１基板１はシート状であってもよい。
（ｉ）その他の層について
上記積層構造において、必要に応じて任意の他の層を挟んでも良い。或いは媒体の最外面に任意の他の層を設けても良い。具体的には、第１反射層３と中間樹脂層４との間、中間樹脂層４と第２記録層５との間、第２反射層６と接着層７との間、などに中間層としてのバッファー層を設けてもよい。
【００８２】
バッファー層は２つの層の混和を防止し、相溶を防ぐものである。バッファー層が混和現象を防止する以外の他の機能を兼ねていても良い。また必要に応じてさらに他の中間層を挟んでも良い。
バッファー層の材料は、第２記録層５や中間樹脂層４と相溶せず、かつ、ある程度の光透過性をもつ必要があるが、公知の無機物及び有機物が用いうる。特性面からは、好ましくは無機物が用いられる。例えば、（１）金属又は半導体、（２）金属又は半導体の酸化物、窒化物、硫化物、酸硫化物、フッ化物又は炭化物、もしくは（３）非晶質カーボン、などが用いられる。中でも、ほぼ透明な誘電体からなる層や、ごく薄い金属層（合金を含む）が好ましい。
【００８３】
具体的には、酸化珪素、特に二酸化珪素や、酸化亜鉛、酸化セリウム、酸化イットリウム等の酸化物；硫化亜鉛、硫化イットリウムなどの硫化物；窒化珪素などの窒化物；炭化珪素；酸化物とイオウとの混合物（酸硫化物）；および後述の合金などが好適である。また、酸化珪素と硫化亜鉛との３０：７０〜９０：１０程度（重量比）の混合物も好適である。また、イオウと二酸化イットリウムと酸化亜鉛との混合物（Ｙ_２Ｏ_２Ｓ−ＺｎＯ）も好適である
金属や合金としては、銀、又は銀を主成分とし更にチタン、亜鉛、銅、パラジウム、及び金よりなる群から選ばれる少なくとも１種の元素を０．１〜１５原子％含有するものが好適である。また、銀を主成分とし、少なくとも１種の希土類元素を０．１〜１５原子％含有するものも好適である。この希土類としては、ネオジウム、プラセオジウム、セリウム等が好適である。
【００８４】
その他、バッファー層作製時に記録層の色素を溶解しないようなものであれば樹脂層でも構わない。特に、真空蒸着やＣＶＤ法で作製可能な高分子膜が有用である。
バッファー層の厚さは２ｎｍ以上が好ましく、より好ましくは５ｎｍ以上である。バッファー層の厚さが過度に薄いと、上記の混和現象の防止が不十分となる虞がある。但し２０００ｎｍ以下が好ましく、より好ましくは５００ｎｍ以下である。バッファー層が過度に厚いと、混和防止には不必要であるばかりでなく、光の透過率を低下させる恐れもある。また無機物からなる層の場合には成膜に時間を要し生産性が低下したり、膜応力が高くなったりする虞があり２００ｎｍ以下が好ましい。特に、金属の場合は光の透過率を過度に低下させるため、２０ｎｍ以下程度が好ましい。
【００８５】
また、記録層や反射層を保護するために保護層を設けても良い。保護層の材料としては、記録層や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。有機物質の材料としては、熱可塑性樹脂、熱硬化性樹脂、電子線硬化性樹脂、紫外線硬化性樹脂等を挙げることができる。また、無機物質としては、酸化ケイ素、窒化ケイ素、ＭｇＦ_２、ＳｎＯ_２等が挙げられる。
【００８６】
熱可塑性樹脂、熱硬化性樹脂などは適当な溶剤に溶解して塗布液を調製し、これを塗布、乾燥することによって形成することができる。紫外線硬化性樹脂は、そのままもしくは適当な溶剤に溶解して塗布液を調製した後にこの塗布液を塗布し、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。紫外線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あるいは混合して用いても良いし、１層だけではなく多層膜にして用いても良い。
【００８７】
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やスパッタ法や化学蒸着法等の方法が用いられるが、この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、本光記録媒体においては、１〜５０μｍが好ましい。
【００８８】
更に、上記光記録媒体には、必要に応じて、記録・再生光の入射面ではない面に、インクジェット、感熱転写等の各種プリンタ、或いは各種筆記具にて記入（印刷）が可能な印刷受容層を設けてもよい。
或いは、本層構成の他に記録層を設けて記録層を３層以上としても良い。また、本層構成の光記録媒体を２枚、第１基板２１を外側にして貼合わせて、記録層を４層有する、より大容量媒体とすることもできる。
（Ｂ）タイプ２
図２は、本実施形態にかかる光記録媒体（タイプ２）を示す模式的な断面図である。
【００８９】
本実施形態にかかるタイプ２の光記録媒体（貼り合わせ型の片面入射型光記録媒体）は、図２に示すように、ディスク状の透明な（光透過性の）第１基板（第１の基板，第１光透過性基板）２１上に、色素を含む第１記録層（第１の記録層，第１色素含有記録層）２２、半透明の第１反射層（半透明反射層）２３、透明接着層（中間層）２４、バッファー層２８、色素を含む第２記録層（第２の記録層，第２色素含有記録層）２５、第２反射層２６、ディスク状の第２基板（第２の基板）２７をこの順に有してなる。光ビームは第１基板２１側から照射され、記録・再生が行われる。なお、透明であるとは光記録媒体の記録・再生に用いる光ビームに対して透明であることを言う。
【００９０】
つまり、本光記録媒体は、案内溝を有する第１基板２１上に、少なくとも、第１の色素を含有する第１記録層２２と第１反射層２３とを順次積層させてなる第１情報記録体と、案内溝を有する第２基板２７上に、少なくとも、第２反射層２６と第２の色素を含有する第２記録層２５とを順次積層させてなる第２情報記録体とを備え、第１情報記録体と第２情報記録体とを基板と反対側の面を対向させ、光学的に透明な接着層を介して貼り合わされてなる。
【００９１】
第１基板２１、第２基板２７上にはそれぞれ凹凸が形成され、それぞれ記録トラックを構成する。記録トラックは凸部及び凹部のどちらでも良いが、第１基板２１上の記録トラック３１は、第１基板２１の溝部、即ち光の入射方向に対して凸部で構成されるのが好ましく、第２基板２７上の記録トラック３２は、第２基板２７の溝部、即ち光の入射方向に対して凹部で構成されるのが好ましい。特に断らない限り、本実施形態において凹凸は記録・再生に用いる光の入射方向に対して定義される。この他に必要に応じ、ランドプリピット等の凹凸ピットを有することもある。
【００９２】
次に、各層について説明する。
本実施形態にかかるタイプ２の光記録媒体の第１基板２１，第１記録層２２，第１反射層２３，第２記録層２５，反射層２６は、それぞれタイプ１の光記録媒体の第１基板１，第１記録層２，半透明反射層３，第２記録層５，第２反射層６と略同様の構成である。
【００９３】
また、中間層としての透明接着層２４は、凹凸により溝やピットを形成する必要がないという以外は、タイプ１の光記録媒体に備えられる中間樹脂層４と略同様の構成である。なお、本タイプ２の光記録媒体では、上記の溝やピットは後述する第２基板２７に形成されている。
さらに、中間層としてのバッファー層２８は、タイプ１の光記録媒体に備えられるバッファー層と略同様の構成である。なお、このバッファー層は必要に応じて形成するようにしても良い。
【００９４】
第２基板２７は、光記録媒体がある程度の剛性を有するよう、形状安定性を備えるのが望ましい。即ち機械的安定性が高く、剛性が大きいことが好ましい。第１基板２１が十分な形状安定性を備えていない場合は、第２基板２７は特に形状安定性が高い必要がある。この点で吸湿性が小さいことが望ましい。
第２基板２７には凹凸（記録トラック）を形成するので成形性がよいことが望ましい。また、透明である必要はないが、製造工程上、透明であると、第２記録層２５の膜厚測定がしやすいので好ましい。
【００９５】
このような材料としては、例えばアクリル系樹脂、メタクリル系樹脂、ポリカーボネート樹脂、ポリオレフィン系樹脂（特に非晶質ポリオレフィン）、ポリエステル系樹脂、ポリスチレン樹脂、エポキシ樹脂等の樹脂からなるもの、ガラスからなるものを用いることができる。
第２基板２７には、凹凸が螺旋状又は同心円状に設けられ、溝及びランドを形成する。通常、このような溝及び／又はランドを記録トラックとして、第２記録層２５に情報が記録・再生される。通常、第２記録層２５は塗布形成されるので溝部で厚膜となり記録再生に適する。本光記録媒体においては第２基板２７の溝部、即ち光の入射方向に対して凹部を記録トラック３２とするのが好ましい。ここで、凹部、凸部はそれぞれ光の入射方向に対する凹部、凸部を言う。通常、溝幅は５０〜５００ｎｍ程度であり、溝深さは１０〜２５０ｎｍ程度である。また記録トラックが螺旋状である場合、トラックピッチは０．１〜２．０μｍ程度であることが好ましい。この他に必要に応じ、ランドプリピット等の凹凸ピットを有してもよい。
【００９６】
このような凹凸を有する第２基板２７は、コストの観点から、凹凸を持つスタンパから樹脂を用いて射出成形により製造するのが好ましい。ガラス等の基体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る場合は、樹脂層に記録トラックなどの凹凸を形成してもよい。
上記のようにして得られた本光記録媒体（タイプ１及びタイプ２）への記録は、記録層に直径０．５〜１μｍ程度に集束したレーザ光を第１基板１，２１側から照射することにより行なう。レーザ光の照射された部分には、レーザ光エネルギーの吸収による、分解、発熱、溶解等の記録層の熱的変形が起こり、光学特性が変化する。
【００９７】
記録された情報の再生は、レーザ光により、光学特性の変化が起きている部分と起きていない部分の反射率の差を読み取ることにより行なう。
また、２層の記録層には以下のようにして個別に記録再生する。集束したレーザの集束位置をナイフエッジ法、非点収差法、フーコー法等で得られるフォーカスエラー信号によって、第１記録層２，２２と第２記録層５，２５とは区別できる。すなわち、レーザ光を集束する対物レンズを上下に動かすと、レーザの集束位置が第１記録層２，２２に対応する位置と第２記録層５，２５に対応する位置で、それぞれＳ字カーブが得られる。どちらのＳ字カーブをフォーカスサーボに用いるかにより、第１記録層２，２２と第２記録層５，２５のどちらを記録再生するかを選択可能である。
【００９８】
タイプ１の光記録媒体において好ましくは、図１に示すように第１基板１及び中間樹脂層４にそれぞれ凹凸が形成されてなり、第１基板１の凸部及び中間樹脂層４の凸部を記録トラックとして記録再生を行なうものとする。通常、色素記録層は塗布形成されるので溝部で厚膜となり記録再生に適する。タイプ１の光記録媒体においては第１基板１の溝部、即ち光の入射方向に対して凸部を記録トラック１１とし、中間樹脂層４の溝部、即ち光の入射方向に対して凸部を記録トラック１２とするのが好ましい。
【００９９】
また、タイプ２の光記録媒体において好ましくは、図２に示すように第１基板２１及び第２基板２７にそれぞれ凹凸が形成されてなり、第１基板２１の凸部及び第２基板２７の凹部を記録トラックとして記録再生を行なうものとする。なお、第１記録層２２と第２記録層２５とでは、トラッキングサーボの極性を逆にする場合がある。タイプ２の光記録媒体においては第１基板２１の溝部、即ち光の入射方向に対して凸部を記録トラック３１とし、第２基板２７の溝部、即ち光の入射方向に対して凹部を記録トラック３２とするのが好ましい。
（２）光記録媒体の記録方法
次に、本実施形態にかかる光記録媒体の記録方法について、図３及び図４を参照しながら具体的に説明する。
【０１００】
図３は、本記録方法を説明するための記録パルスストラテジの概略を示す図である。また、図４は、本記録方法を表した記録パルスストラテジの概略を説明するための図である。
ここで、図３及び図４中、ファーストパルスはマークの始端領域を形成するレーザを照射するためのパルスであり、マルチパルスはマークの中間領域を形成するレーザを照射するためのパルスであり、ラストパルスはマークの終端領域を形成するレーザを照射するためのパルスである。また、Ｔはパルスストラテジを決める際の基準として用いられる基準クロック周期、Ｔ_ｔｏｐ、Ｔ_ｍｐ、Ｔ_ｌｐはそれぞれファーストパルス、マルチパルス、ラストパルスのパルス幅を示しており、ｄＴ_ｔｏｐはファーストパルスのトリガとなる基準クロックとファーストパルスの前エッジとの時間差を示している。
【０１０１】
本記録方法では、記録すべき３Ｔから１４Ｔまでのマーク長に応じて、図３に示すファーストパルス、マルチパルス、ラストパルスを組み合わせて記録用レーザ（記録レーザ，記録用レーザ光）を照射し、情報信号となるマークを形成する。
例えば、長さ３Ｔのマーク（３Ｔマーク）を形成する場合にはファーストパルスを、長さ４Ｔのマーク（４Ｔマーク）を形成する場合にはファーストパルスとラストパルスを、長さ５Ｔのマーク（５Ｔマーク）を形成する場合にはファーストパルスとマルチパルス、さらにラストパルスを、長さ６Ｔ以降のマーク（６Ｔマーク等）を形成する場合は、さらにマルチパルスを一つずつ増加させていくことにより記録用レーザを照射し、３Ｔから１４Ｔまでの異なるマーク長のマークを形成するようになっている。
【０１０２】
ところで、例えばデュアルレイヤタイプの片面入射型ＤＶＤ−Ｒなどのように、片面側からレーザ光を照射して複数の記録層に対して情報の記録又は再生を行なう片面入射型光記録媒体では、例えば片面型ＤＶＤ−Ｒや両面型ＤＶＤ−Ｒのようなレーザ光を基板のみを通して記録層に照射する光記録媒体と同様の記録パルスストラテジを用いて情報信号となるマークを形成すると、再生信号のジッタが悪くなってしまう。
【０１０３】
このようにジッタが悪くなってしまうのは、明確な理由は不明だが、以下のような理由が推測される。
例えばデュアルレイヤタイプの片面入射型ＤＶＤ−Ｒの第２記録層に信号を記録する際には、第１基板、第１記録層、半透明の第１反射層及び中間層を透過したレーザ光が記録用レーザ光（記録レーザともいう）として用いられることになる。このように、第１記録層と第２記録層の間に中間層、半透明の第１反射層等が存在するため、第２記録層に到達する記録用レーザ光の強さ（パワー）が弱められ、また、第１記録層、第１反射層、中間層の各層間の屈折率差によって記録用レーザ光の波長が変化してしまい、第１記録層に信号を記録する場合に対して記録用レーザ光の状態が変化してしまうことになる。
【０１０４】
また、第１記録層にマークを形成する場合も、通常の反射層よりも薄いため蓄熱しにくく、また通常の反射層よりも反射率が低い半透明の第１反射層を利用してマークを形成することになるため、照射したレーザ光の熱が十分に第１記録層に伝わらない。
さらに、記録層はある程度の熱量を受けた後に分解等を開始して、マークを形成し始めるため、分解を始めるためには最初にある程度の熱量が必要になる。このため、実際にレーザ光を照射したとしても、マークが形成され始めるまでに多少の遅れが生じてしまう。この結果、実際に形成されるマークの長さ（マーク長）が、形成したいマーク長よりも短くなってしまう傾向がある。この傾向は形成するマーク長が長く、レーザ光により照射される熱量が少なくなればなるほど顕著となる。
【０１０５】
また、第２記録層においては、通常の片面型記録媒体等に用いる色素よりも高感度の色素を用いるため、マークが形成されはじめた後、主にマークの終端領域が広がりやすい。この傾向はマーク長が長くなるほど顕著である。
これらの原因が組み合わさることにより、例えばデュアルレイヤタイプの片面入射型ＤＶＤ−Ｒなどの片面入射型光記録媒体において、上述の片面型ＤＶＤ−Ｒや両面型ＤＶＤ−Ｒのようなレーザ光を基板のみを通して記録層に照射する光記録媒体と同様の記録パルスストラテジを用いて情報信号となるマークを形成すると、再生信号のジッタが悪くなってしまうと推測される。
【０１０６】
そこで、各記録層の再生信号のジッタを低減して良好なものとすべく、例えばデュアルレイヤタイプの片面入射型ＤＶＤ−Ｒなどの片面入射型光記録媒体において、記録用レーザ光の入射側（第１基板側）から遠い側に位置する記録層（第２記録層）にマークを形成する場合に、第１記録層及び第１記録層と第２記録層との間に介在する層の厚さや屈折率等を考慮して、記録用レーザ光の入射側に近い側に位置する記録層（第１記録層）にマークを形成する場合よりも記録用レーザ光のパワーを上げることが考えられる。
【０１０７】
しかしながら、単に記録用レーザ光のパワーを上げるだけでは、十分にジッタを低減することはできない。
一方、記録用レーザの制御及び記録装置の実用化を考慮すると、記録用レーザ光のパワーはできるだけ低く抑えるのが望ましい。また、記録用レーザ光のパワーを上げていくと、これに伴ってアシンメトリの値が悪くなってしまうため、記録用レーザ光のパワーを上げるとしても限界がある。
【０１０８】
また、記録用レーザ光のパワーを下げすぎると、モジュレーション［最大信号振幅（最大マークの振幅；Ｍｏｄｕｌａｔｉｏｎ；Ｉ１４／Ｉ１４Ｈ）］の値が悪くなってしまう。
特に、従来の片面型記録媒体等では問題とならなかったマーク終端領域の広がりを抑えるために、新たな観点からの記録方法が必要である。
そこで、本実施形態では、記録用レーザ光の入射側（第１基板側）から遠い側に位置する記録層（第２記録層）にマークを形成する場合（即ち、他の記録層を介してパルス状の記録用レーザ光を照射してマークを形成する場合）、アシンメトリの値が所望の範囲内（例えば０付近）［ここではモジュレーションの値も所望の値以上（例えば０．６以上）］になるように記録レーザ光のパワーを調整した上で、以下に説明するように記録方法を工夫して、ジッタを低減させるようにしている。
【０１０９】
特に、アシンメトリの値が所望の範囲内（例えば０付近）となり、ジッタが所定値（例えば９％）以下になる記録レーザ光のパワーのうち最も低いものを選べば、記録用レーザ光のパワーを低く抑えることができる。なお、モジュレーションの値は所望の値以上（例えば０．６以上）となるようにするのが好ましい。
本実施形態では、片面側から記録レーザを照射して複数の記録層に対して情報信号となるマークを形成する光記録媒体において、マークの始端領域を形成するためのファーストパルスと、マークの終端領域を形成するためのラストパルスとを照射し、さらに、ファーストパルスの前エッジの位置及び／又はラストパルスの後エッジの位置をマークの長さに応じて変化させてマークを形成するようにしている。
【０１１０】
これは、ファーストパルスの前エッジの位置やラストパルスの後エッジの位置によって、形成されるマークの始端領域や終端領域の形状が決まり、ジッタに与える影響が大きいためである。
特に、図４（Ａ）に示すような記録パルスストラテジに基づいてマークを形成する場合、図３及び図４（Ｂ）に示すように、形成したいマークの長さに合わせて、図３のファーストパルスの後エッジを移動させることなく（後エッジを固定して）、前エッジのみを移動させて（前エッジをｄＴ_ｔｏｐだけシフトさせて）、ファーストパルスのパルス幅Ｔ_ｔｏｐを広くする（記録用レーザ光の照射時間を長くする）のが好ましい。すなわち、ｄＴ_ｔｏｐの値を増加させ、ファーストパルスの開始タイミングを早め、ファーストパルスのパルス幅Ｔ_ｔｏｐを広く（照射時間を長く）することで、一つのマークを形成するために照射する記録用レーザ光の全照射量を増やすとともに、マークの形成を開始するのに必要な初期熱量を増やすようにするのが好ましい。
【０１１１】
このように、ファーストパルスのパルス幅を広くして記録用レーザ光の照射量を増やしているのは、記録用レーザ光の照射によって記録層に与えられる熱量は記録層中を伝導していくため、所望の長さのマークを形成するために記録用レーザ光を一定時間照射する場合、最初に十分な量の熱量を与える方が、記録層に与えられる熱を有効に利用することができ、マークの広がりを抑えることができるからである。
【０１１２】
ここでは、マークの長さに応じてファーストパルスの前エッジの位置を変化させることで、マークの長さが長くなるほどファーストパルスのパルス幅を広くするようにしている。特に、４Ｔマークから１４Ｔマークまで適宜グループに分けて段階的にファーストパルスのパルス幅を広くしていくのが好ましい。
特に、このようなファーストパルスのパルス幅を広くするという記録方法は、上述のタイプ１及びタイプ２のいずれの構造の光記録媒体に適用しても、ジッタを低減するという効果が得られる。
【０１１３】
なお、ファーストパルスの後エッジを移動させることは好ましくない。後エッジを移動させた場合、レーザの照射開始が遅れることになるため、マークの形成開始が遅れてしまう。これにより、ジッタに悪影響を与えることとなるからである。
また、図４（Ｃ）に示すように、形成したいマークの長さに合わせて、図３のラストパルスの後エッジを移動させて（ｄＴ_ｌｐだけシフトさせる）、ラストパルスのパルス幅Ｔ_ｌｐを狭くする（記録用レーザ光の照射時間を短くする）のも好ましい。なお、ｄＴ_ｌｐは、基本となるラストパルス（例えば第１記録層への記録の際に用いられる記録パルスストラテジのラストパルス）の後エッジとラストパルスのパルス幅を狭くした場合の後エッジとの時間差である。
【０１１４】
ここでは、マークの長さに応じてラストパルスの後エッジの位置を変化させることで、マークの長さが長くなるほどラストパルスのパルス幅を狭くするようにしている。特に、４Ｔマークから１４Ｔマークまで適宜グループに分けて段階的にラストパルスのパルス幅を狭くするのが好ましい。
記録用レーザ光をある一定時間以上照射してマークを形成する場合、マークの終端領域では、記録層は既に十分な熱量を持っており、その熱を利用してマークを形成することができる。この場合、マーク終端領域に熱量を与えすぎると、不必要に大きなマークが形成されてしまうことになる。よって、マークの後端領域を形成するラストパルスの後エッジを短くすると、マークが広がるのを抑えることができ、ジッタが良くなると考えられる。
【０１１５】
ここでは、マークの長さが長いほど、記録用レーザ光の照射時間が長くなり、余分な熱量が与えられやすく、マークが広がりやすいため、マークの長さが長くなるほどラストパルスのパルス幅を狭くして、マークの長さに応じてマークの形成に必要な熱量が与えられるようにしている。
特に、このようなラストパルスのパルス幅を狭くする記録方法は、上述のタイプ１及びタイプ２のいずれの構造の光記録媒体に適用しても、ジッタを低減するという効果は得られるが、特にタイプ２の光記録媒体に適用すると効果が大きい。
【０１１６】
つまり、本実施形態にかかるタイプ２の光記録媒体では、第２記録層２５のランド部に記録するが、第２記録層２５のランド部の膜厚は薄い。一般に、記録層の膜厚が薄いと、マークの形成に必要な熱量も少なくなり、記録層の感度が上がることとなる。よって、記録感度の良いタイプ２の光記録媒体において、ラストパルスの後エッジ位置を補正して（前に移動させて）パルス幅を狭く（照射時間を短く）することは、不必要なマークの広がりを抑えることができ、特に効果が大きい。
【０１１７】
なお、ファーストパルスの前エッジ位置及びラストパルスの後エッジの位置をどの程度変化させるかについては、光記録媒体の構成や照射するレーザ光のパワーや波長により、適宜、実験的に決められるものであり、一概には言えないが、一般にファーストパルスの前エッジ位置の移動幅は、ファーストパルスのパルス幅の５％以上、５０％以下であり、ラストパルスの後エッジ位置の移動幅は、ラストパルスのパルス幅の５％以上、５０％以下である。
【０１１８】
さらに、図４（Ｄ）に示すように、ラストパルスに対応する記録用レーザ光のパルス成分よりもファーストパルスに対応する記録用レーザ光のパルス成分の最大パワーを大きくするのも好ましい。
上述したように、マークの始端領域を形成するには最初にある程度の熱量が必要となる。しかし、照射する記録レーザ全体の照射パワーを増加させた場合、不必要な熱量をも与えることとなり、マークが広がってしまうこととなる。よって、ファーストパルスに対応する記録用レーザ光のパルス成分の最大パワーを上げて瞬間的に大きな熱量を与え、即ち、マークの始端領域の形成開始に必要な初期熱量のみを上げて、マークを形成するのが好ましい。
【０１１９】
なお、このように、ファーストパルスに対応する記録用レーザ光のパワーを、マルチパルスやラストパルスに対応する記録用レーザ光のパワーよりも大きくする場合（これをＰｏｗｅｒｅｄという）、ファーストパルス，マルチパルス及びラストパルスに対応する記録用レーザ光のパワーを同一にする場合よりも、マルチパルスやラストパルスに対応する記録用レーザ光のパワーを下げることができるため、全体として、記録用レーザ光のパワーを下げることができることになる。これは、ファーストパルスに対応して照射される記録用レーザ光のパワーを上げると、瞬間的に大きな熱量が与えられ、与えられた熱量が記録層を伝導するため、マルチパルスやラストパルスに対応する記録用レーザ光のパワーを下げることが可能になると考えられる。
【０１２０】
ここで、ファーストパルスに対応する記録用レーザのパルス成分とラストパルス（又はマルチパルス）に対応する記録用レーザのパルス成分のパワーの差としては、ファーストパルスに対応する記録用レーザのパルス成分のパワーを、ラストパルス（又はマルチパルス）に対応する記録用レーザのパルス成分のパワーよりも５％以上、好ましくは１０％以上大きくするのが好ましい。この値以上であれば、マークの形成を遅らせること無く、効果的にマークの始端領域を形成することが出来るからである。
【０１２１】
また、その差は３０％以下、好ましくは２０％以下であることが好ましい。あまり差を付けてしまうと、マーク長が長くなるにつれてマークの始端領域と後端領域の形状がアンバランスとなり、また、モジュレーションが低下するなど再生特性が悪くなってしまうからである。
特に、このようにファーストパルスに対応して照射される記録用レーザ光のパワーを上げる記録方法は、上述のタイプ１及びタイプ２のいずれの構造の光記録媒体に適用しても、ジッタを低減するという効果は得られるが、特にタイプ２の光記録媒体に適用すると効果が大きい。
【０１２２】
つまり、本実施形態にかかるタイプ２の光記録媒体では、第２記録層２５のランド部に記録するが、第２記録層２５のランド部の膜厚は薄い。一般に、記録層の膜厚が薄いと、マークの形成に必要な熱量も少なくなり、記録層の感度が上がることとなる。よって、記録感度の良いタイプ２の光記録媒体において、ファーストパルスに対応して照射される記録用レーザ光のパワーを上げることは、不必要なマークの広がりや隣のトラックへの信号の漏れこみを抑えることができ、特に効果が大きい。
【０１２３】
なお、本発明の片面側から記録レーザを照射して複数の記録層に対して情報信号となるマークを形成する光記録媒体の記録方法において、必ずしも上記の記録方法の全てを用いる必要はなく、所望の再生特性が得られるように、これらの記録方法を適宜組み合わせて記録すればよい。
一般に、デュアルレイヤ媒体の第１記録層にマークを形成する場合は、ファーストパルスの前エッジ及びラストパルスの後エッジを補正すると十分な再生特性を得られることが多い。
【０１２４】
特に、タイプ１のデュアルレイヤ媒体の第２記録層にマークを形成する場合は、ファーストパルスの前エッジを補正するだけで十分な再生特性を得られることが多い。一方、タイプ２のデュアルレイヤ媒体の第２記録層にマークを形成する場合は、ファーストパルスの前エッジを補正する記録方法と、ラストパルスの後エッジを補正する記録方法と、ラストパルス（又はマルチパルス）に対応する記録用レーザのパルス成分よりもファーストパルスに対応する記録用レーザのパルス成分の最大パワーを大きくする記録方法とを組み合わせて記録すると十分な再生特性が得られやすい。
【０１２５】
また、本発明では５Ｔ以上のマークを形成する際に、マルチパルスレーザ（マルチパルスに対応する記録用レーザ）を照射しているが、マルチパルスレーザのパルス幅等も適宜変化させても良い。
したがって、本実施形態にかかる光記録媒体の記録方法によれば、片面側からレーザ光を照射して複数の記録層に対して情報の記録又は再生を行なう光記録媒体に、マークの始端領域の形成開始、及び終端領域の形成終了を所望のマーク長に合わせて制御できることから、ジッタを低く抑えた良好な再生特性を持つ信号を形成することができるという利点がある。また、本発明によれば、記録パワーが変動したとしても安定して信号を形成することができるという利点もある。
【０１２６】
また、本実施形態にかかる光記録媒体の記録方法によれば、第２記録層にパルス状の記録用レーザ光を照射してマークを形成する場合、アシンメトリの値が所望の範囲内になるように［ここではモジュレーションの値も所望の値以上（例えば０．６以上）になるように］記録レーザ光のパワーを調整するとともに、マークの長さに応じてマークの始端領域を形成するためのファーストパルスのパルス幅又はマークの終端領域を形成するためのラストパルスのパルス幅を変化させるため、アシンメトリの値が所望の範囲内（例えば０付近）になるように［ここではモジュレーションの値も所望の値以上（例えば０．６以上）になるように］しながら、ジッタを所定値（例えば９％）以下に低減させることができる。
【０１２７】
この場合、アシンメトリの値が所望の範囲内（例えば０付近）となり［ここではモジュレーションの値も所望の値以上（例えば０．６以上）となり］、ジッタが所定値以下（例えば９％以下）になる記録レーザ光のパワーのうち最も低いものを選択すれば、記録レーザ光のパワーを低く抑えることができる。
なお、上述の実施形態では、記録用レーザ光の入射側（第１基板側）から遠い側に位置する記録層（第２記録層）にマークを形成する場合の記録方法について説明したが、記録用レーザ光の入射側（第１基板側）に近い側に位置する記録層（第１記録層）にマークを形成するには、例えば片面型ＤＶＤ−Ｒや両面型ＤＶＤ−Ｒのようなレーザ光を基板のみを通して記録層に照射する光記録媒体と同様の記録パルスストラテジを用いれば良い。
【０１２８】
但し、例えば複数の記録層を有し、片面側からレーザ光を照射することでそれぞれの記録層に情報の記録又は再生を行なうことができる片面入射型光記録媒体の場合、第１記録層への記録には半透明反射層が用いられるため、この半透明反射層の影響を考慮すると、第１記録層にマークを形成するとき［即ち、他の記録層を介さずに（記録用レーザ光の入射側に最も近い側に位置する記録層に）パルス状の記録用レーザ光を照射してマークを形成するとき］にも、マークの長さに応じてマークの始端領域を形成するためのファーストパルスの前エッジの位置（ファーストパルスのパルス幅）及び／又はマークの終端領域を形成するためのラストパルスの後エッジの位置（ラストパルスのパルス幅）を変化させるのが好ましい。
【０１２９】
具体的には、マークの長さが長くなるほどマークの始端領域を形成するためのファーストパルスのパルス幅を広くするのが好ましい。特に、４Ｔマークから１４Ｔマークまで適宜グループに分けて段階的にファーストパルスのパルス幅を広くしていくのが好ましい。
また、マークの長さが長くなるほどマークの終端領域を形成するためのラストパルスのパルス幅を狭くするのが好ましい。特に、４Ｔマークから１４Ｔマークまで適宜グループに分けて段階的にラストパルスのパルス幅を狭くするのが好ましい。
【０１３０】
このように、第１記録層に（他の記録層を介さずに）パルス状の記録用レーザ光を照射してマークを形成する場合に、マークの長さに応じてファーストパルスの前エッジの位置及び／又はラストパルスの後エッジの位置を変化させれば、ジッタを低減させることができる。
この場合、アシンメトリの値が所望の範囲内（例えば０付近）になるように［ここではモジュレーションの値も所望の値以上（例えば０．６以上）になるように］記録レーザ光のパワーを調整するのが好ましい。
【０１３１】
このように、アシンメトリの値が所望の範囲内になるように［ここではモジュレーションの値も所望の値以上（例えば０．６以上）になるように］記録レーザ光のパワーを調整するとともに、マークの長さに応じてマークの始端領域を形成するためのファーストパルスのパルス幅を変化させることで、アシンメトリの値が所望の範囲内（例えば０付近）になるように［ここではモジュレーションの値も所望の値以上（例えば０．６以上）になるように］しながら、ジッタを所定値（例えば９％）以下に低減させることができる。
【０１３２】
この場合、ジッタが所定値以下になる記録レーザ光のパワーのうち最も低いものを選択すれば、記録レーザ光のパワーを低く抑えることができる。
なお、ここでは、色素含有記録層を含む追記型光記録媒体（ここではＤＶＤ−Ｒ，ＤＶＤ＋Ｒ）について説明したが、光記録媒体はこれに限られるものではなく、片面側からのレーザ光の照射により情報を記録又は再生しうる複数の記録層を備える光記録媒体であれば良い。例えば、記録層として例えば結晶状態の部分を未記録状態・消去状態とし、非晶質状態の部分を記録状態とする相変化型記録層を含む書換型光記録媒体（例えばＤＶＤ−ＲＷ，ＤＶＤ＋ＲＷ，ＤＶＤ−ＲＡＭなど）や記録層として磁性記録層を含む光磁気型の光記録媒体であっても良い。
【０１３３】
また、ここでは、本発明を、片面側からのレーザ光の照射により情報を記録又は再生しうる２つの記録層を備える光記録媒体に適用する場合について説明したが、これに限られるものではなく、例えば３層以上の記録層を備え、片面側からのレーザ光の照射により情報を記録又は再生しうる光記録媒体に適用することもできる。
【０１３４】
また、本実施形態では、光記録媒体の記録方法について説明したが、この記録方法に基づいて設定される記録パルスストラテジ（ライトストラテジ）は、例えば光記録媒体の記録装置に搭載される。
つまり、光記録媒体の記録装置（ドライブ，ライタ）は、光記録媒体を回転駆動するスピンドルモータと、例えばレーザダイオード（ＬＤ）などの半導体レーザ（レーザ光源），ビームスプリッタ，対物レンズ，例えばフォトダイオード（ＰＤ）などの光検出器を含む光ピックアップと、半導体レーザを駆動するレーザドライバ（駆動部；例えば駆動回路）と、記録しようとするデータに基づいてレーザドライバに対して出力するパルス（信号）の制御［記録用レーザ光のパワー変調制御（マルチパルス変調制御）］を行なう記録パルスストラテジ回路（記録パルスストラテジ制御部）と、各デバイスに対する制御を行なう制御演算部［例えばＣＰＵやメモリ（記憶部）を含む］とを備えて構成される。なお、記録パルスストラテジ回路と制御演算部とを合わせて記録用レーザ制御部という。
【０１３５】
そして、制御演算部に記録命令（書込命令）が入力されると、制御演算部が制御信号を出力し、記録パルスストラテジ回路でパワー変調制御された信号に基づいてレーザドライバが半導体レーザを駆動する。これにより、半導体レーザからビームスプリッタ，対物レンズなどを介して光記録媒体の所望の記録層にレーザ光（記録光）を照射し、データ記録が行なわれるようになっている。
【０１３６】
このため、記録用レーザ制御部を構成する記録パルスストラテジ回路に、上述の記録方法に基づいて決められた記録パルスストラテジ（記録パルス変調パターン）を設定すれば良い。これにより、記録パルスストラテジ回路に設定された記録パルスストラテジに基づいてパワー変調制御が行なわれ、これに基づいて半導体レーザから記録用レーザ光が照射され、所望のマークが形成されて情報が記録されることになる。
【０１３７】
なお、本発明は上記の実施形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲で種々変形して実施することができる。
【０１３８】
【実施例】
以下に実施例を示すが、本発明はその要旨を越えない限り、以下の実施例に限定されるものではない。なお、実施例中の％は、特に断らない限り総て重量基準である。
（光記録媒体の作製）
本実施例ではタイプ１とタイプ２の２つのタイプの光記録媒体を作製した。
【０１３９】
まず、タイプ１の光記録媒体は、以下のようにして作製した。
Ｎｉスタンパを用いて、ポリカーボネートを射出成形して、溝ピッチ０．７４μｍ、溝幅０．３μｍ、溝深さ１３０〜１７０ｎｍのランド及びプリピットを有する直径１２０ｍｍ、厚さ０．６ｍｍの第１の基板を作製した。次に、含金属アゾ色素の０．２％オクタフルオロペンタノール溶液を第１の基板上にスピンコート法により塗布し、１００℃で３０分間加熱処理して第１の記録層を形成した（最大吸収波長（λｍａｘ）約６００ｎｍ）。次に、Ａｇを９７原子％以上含むＡｇ合金を１５〜２０ｎｍの厚さにスパッタリングし、透過率４０％以上の第１反射層を形成した。以上により第１情報記録基板を作製した。
【０１４０】
次に、この第１反射層の上に、紫外線硬化性樹脂を、厚さ２５〜４０μｍにそれぞれ塗布し、予め作製した樹脂スタンパを凹凸面を第１の基板側に向けて載置し、続いて、樹脂スタンパ側から紫外線を照射し、紫外線硬化性樹脂が硬化した後、樹脂スタンパを剥離して、第１基板と同様に、溝ピッチ０．７４μｍ、溝幅０．３μｍ、溝深さ１３０〜１７０ｎｍのランド及びプリピットを形成した。
【０１４１】
次に、中間層の上に、第１の記録層に使用したのと同じ含金属アゾ色素の０．２％オクタフルオロペンタノール溶液をスピンコート法により塗布し、１００℃で３０分間加熱処理して第２の記録層を形成した後、Ａｇを９７原子％以上含むＡｇ合金を１００〜１５０ｎｍの厚さにスパッタリングし、第２の反射層を形成し、この上に、紫外線硬化性樹脂からなる厚さ５〜１０μｍの保護層を設け、さらに、この保護層上に、紫外線硬化性樹脂からなる接着剤（日本化薬製ＤＶＤ５７６Ｍ）を、厚さ４０〜７０μｍに塗布し、予め作製した、直径１２０ｍｍ、厚さ０．６ｍｍのポリカーボネート製の第２の基板を載置し、続いて、第２の基板側から紫外線を照射して、接着層を硬化させてタイプ１の光記録媒体を作製した。
【０１４２】
一方、タイプ２の光記録媒体は、以下のようにして作製した。
Ｎｉスタンパを用いて、ポリカーボネートを射出成形して、溝ピッチ０．７４μｍ、溝幅３５０ｎｍ、溝深さ３０〜７０ｎｍのランド及びプリピットを有する直径１２０ｍｍ、厚さ０．６ｍｍの第１の基板を作製した。次に、Ａｇを９７原子％以上含むＡｇ合金を１００ｎｍの厚さにスパッタリングし、第２反射層を形成した。次に、含金属アゾ色素の０．２％オクタフルオロペンタノール溶液を第２反射層上にスピンコート法により塗布し、１００℃で３０分間加熱処理して第２の記録層を形成した（最大吸収波長（λｍａｘ）約６００ｎｍ）。次に、この第２色素含有記録層上に、Ａｇを含む９７％以上含む銀合金をスパッタしてバッファー層を形成し、その上に紫外線樹脂（日本化薬製ＳＰＣ−９２０）を膜厚約５〜７ｕｍの厚さにスピンコートして、保護層を形成した。
【０１４３】
そして、この保護層上に、ラジカル系紫外線硬化樹脂（接着剤）（日本化薬製ＤＶＤ５７６Ｍ）をスピンコートして塗布し、別途製作したタイプ１の光記録媒体の作製に説明した第１情報基板と貼り合わせてタイプ２の光記録媒体を作製した。
（信号記録及び評価方法）
波長６５７ｎｍ（ＮＡ＝０．６５）の半導体レーザを搭載した評価機（パルステック社製ＤＤＵ−１０００、最大記録パワー１５ｍＷ）を用い、記録線速密度３．８ｍ／ｓ、基準クロック周期３８．５ｎｓ（１／２６Ｍｂｐｓ）、８−１６変調のＥＦＭ＋信号を、記録信号のアシンメトリが０付近となる（ここではモジュレーションが０．６以上になる）記録パワーでマーク長３Ｔ〜１４Ｔのマークを記録した。その後記録信号を再生線速密度３．８ｍ／ｓ、再生パワー０．７ｍＷで信号を再生し、マーク長３Ｔ〜１４Ｔのマークの再生信号のジッタ（信号のずれ）の平均値を測定した。
（実施例１）
上述のようにして作製したタイプ１の光記録媒体の第１記録層に、表１に示す記録パルスストラテジに従い、ファーストパルスとラストパルスをマークの長さに合わせて変化させて信号を記録し、その後信号を再生して再生信号のジッタを測定した。ジッタ（縦軸）と記録用レーザのパワー（横軸）を測定した測定結果を図５に示す。
【０１４４】
【表１】

【０１４５】
（実施例２）
表２に示す記録パルスストラテジに従い、ファーストパルスをマークの長さに合わせて変化させた以外は実施例１と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。ジッタ（縦軸）と記録用レーザのパワー（横軸）を測定した測定結果を図５に示す。
【０１４６】
【表２】

【０１４７】
（実施例３）
表３に示す記録パルスストラテジに従い、ラストパルスをマークの長さに合わせて変化させた以外は実施例１と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。ジッタ（縦軸）と記録用レーザのパワー（横軸）を測定した測定結果を図５に示す。
【０１４８】
【表３】

【０１４９】
（実施例４）
タイプ１の光記録媒体の第２記録層に、表４に示す記録パルスストラテジに従い、ファーストパルスをマークの長さに合わせて変化させて信号を記録し、その後信号を再生して再生信号のジッタを測定した。ジッタ（縦軸）と記録用レーザのパワー（横軸）を測定した測定結果を図６に示す。
【０１５０】
【表４】

【０１５１】
（実施例５）
タイプ２の光記録媒体の第２記録層に、表５に示す記録パルスストラテジに従いファーストパルスとラストパルスをマークの長さに合わせて変化させた以外は実施例１と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。ジッタ（縦軸）と記録用レーザのパワー（横軸）を測定した測定結果を図７及び図８に示す。
【０１５２】
【表５】

【０１５３】
（実施例６）
表６に示す記録パルスストラテジに従い、ファーストパルスをマークの長さに合わせて変化させた以外は実施例５と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。ジッタ（縦軸）と記録用レーザのパワー（横軸）を測定した測定結果を図７に示す。
【０１５４】
【表６】

【０１５５】
（実施例７）
表７に示す記録パルスストラテジに従い、ラストパルスをマークの長さに合わせて変化させた以外は実施例５と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。ジッタ（縦軸）と記録用レーザのパワー（横軸）を測定した測定結果を図７に示す。
【０１５６】
【表７】

【０１５７】
（実施例８）
表８に示す記録パルスストラテジに従い、ファーストパルスに対応する記録用レーザーのパルス成分のパワーを１０％上げた以外は実施例５と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。ジッタ（縦軸）と記録用レーザのパワー（横軸）を測定した測定結果を図８に示す。なお、図８の横軸の記録用レーザのパワーはラストパルスのパワー値を示している。
【０１５８】
【表８】

【０１５９】
（実施例９）
表９に示す記録パルスストラテジに従い、ファーストパルスに対応する記録用レーザのパルス成分のパワーを２０％上げた以外は実施例５と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。ジッタ（縦軸）と記録用レーザのパワー（横軸）を測定した測定結果を図８に示す。なお、図８の横軸の記録用レーザのパワーはラストパルスのパワー値を示している。
【０１６０】
【表９】

【０１６１】
（比較例１）
表１０に示す従来技術の記録パルスストラテジに従いファーストパルス、ラストパルスをマークの長さに合わせて変化させることなく、実施例１と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。測定結果を図５に示す。
【０１６２】
【表１０】

【０１６３】
（比較例２）
表１１に示す従来技術の記録パルスストラテジに従いファーストパルス、ラストパルスをマークの長さに合わせて変化させることなく、実施例４と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。測定結果を図６に示す。
【０１６４】
【表１１】

【０１６５】
（比較例３）
表１２に示す従来技術の記録パルスストラテジに従いファーストパルス、ラストパルスをマークの長さに合わせて変化させることなく、実施例５と同様に信号を記録し、その後信号を再生して再生信号のジッタを測定した。測定結果を図７に示す。
【０１６６】
【表１２】

【０１６７】
（まとめ）
図５は、タイプ１の光記録媒体の第１記録層に信号を記録した際の記録用レーザのパワー及び再生信号のジッタの関係を示す図である。
図５を見ると明らかなように、ファーストパルスとラストパルスを変化させた実施例１では、何も変化させない比較例１と比べてジッタが改善されている。また、実施例１では記録パワーが変化してもジッタの値はさほど変動せず、低い値で安定している。よって、記録用レーザのパワー変動に対するマージンが大きく、安定して信号の記録を行なうことが出来る。
【０１６８】
また、ファーストパルスのみを変化させた実施例２及びラストパルスのみを変化させた実施例３においても、比較例１と比べてジッタが改善され、また記録用レーザのパワー変動に対するマージンが大きくなっており、本発明の効果が証明されている。
図６は、タイプ１の光記録媒体の第２記録層に信号を記録した際の記録用レーザのパワー及び再生信号のジッタの関係を示す図である。
【０１６９】
図６を見ると明らかなように、ファーストパルスを変化させた実施例４では、何も変化させない比較例２と比べてジッタが改善されている。また、実施例４では記録パワーが変化してもジッタの値はさほど変動せず、低い値で安定している。よって、記録用レーザのパワー変動に対するマージンが大きく、安定して信号の記録を行なうことが出来る。
【０１７０】
図７は、タイプ２の光記録媒体の第２記録層に信号を記録した際の記録用レーザのパワー及び再生信号のジッタの関係を示す図である。
図７を見ると明らかなように、ファーストパルスとラストパルスを変化させた実施例５では、何も変化させない比較例３と比べてジッタが改善されている。また、実施例５では比較例３と比べて、ジッタを低く抑えることができる最適記録パワー付近でのジッタの変動が小さく、記録用レーザのパワー変動に対するマージンが大きく、安定して信号の記録を行なうことが出来る。
【０１７１】
また、ファーストパルスのみを変化させた実施例６及びラストパルスのみを変化させた実施例７においても、比較例３と比べジッタが改善され、また記録用レーザのパワー変動に対するマージンが大きくなっている。
図８は、タイプ２の光記録媒体の第２記録層に信号を記録した際にファーストパルスに対応する記録用レーザのパルス成分のパワーを変化させた場合の記録用レーザのパワー及び再生信号のジッタの関係を示す図である。
【０１７２】
図８を見ると明らかなように、ファーストパルスに対応する記録用レーザのパルス成分のパワーを１０％上げた実施例８及びパワーを２０％上げた実施例９は、何もパワーを変化させていない実施例５と比べてジッタが改善されている。
【０１７３】
【発明の効果】
本発明の光記録媒体の記録方法及び記録装置によれば、片面側からレーザ光を照射して複数の記録層に対して情報の記録又は再生を行なう光記録媒体に、マークの始端領域の形成開始、及び終端領域の形成終了を所望のマーク長に合わせて制御できることから、ジッタを低く抑えた良好な再生特性を持つ信号を形成することができるという利点がある。また、本発明によれば、記録パワーが変動したとしても安定して信号を形成することができるという利点もある。
【図面の簡単な説明】
【図１】本発明の一実施形態にかかる光記録媒体（タイプ１）を示す模式的断面図である。
【図２】本発明の一実施形態にかかる光記録媒体（タイプ２）を示す模式的断面図である。
【図３】本発明の一実施形態にかかる光記録媒体の記録方法を説明するための記録パルスストラテジの概略を示す模式図である。
【図４】本発明の一実施形態にかかる光記録媒体の記録方法を表した記録パルスストラテジの概略を示す模式図である。
【図５】本発明の実施例にかかる光記録媒体（タイプ１）の第１記録層に信号を記録した際の記録用レーザのパワー及び再生信号のジッタの関係を示す図である。
【図６】本発明の実施例にかかる光記録媒体（タイプ１）の第２記録層に信号を記録した際の記録用レーザのパワー及び再生信号のジッタの関係を示す図である。
【図７】本発明の実施例にかかる光記録媒体（タイプ２）の第２記録層に信号を記録した際の記録用レーザのパワー及び再生信号のジッタの関係を示す図である。
【図８】本発明の実施例にかかる光記録媒体（タイプ２）の光記録媒体の第２記録層に信号を記録した際にファーストパルスに対応する記録用レーザのパルス成分のパワーを変化させた場合の記録用パワー及び再生信号のジッタの関係を示す図である。
【符号の説明】
１，２１ 第１基板（第１の基板）
２，２２ 第１記録層（第１の記録層）
３，２３ 第１反射層
４ 中間樹脂層（中間層）
５，２５ 第２記録層（第２の記録層）
６，２６ 第２反射層
７ 接着層
８，２７ 第２基板（第２の基板）
２８ バッファー層
１１，１２，３１凸部からなる記録トラック
２４ 透明接着層（中間層）
３２ 凹部からなる記録トラック[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium recording method and recording apparatus, and more particularly to an optical recording medium recording method and recording apparatus having a plurality of recording layers capable of high density recording.
[0002]
[Prior art]
Currently, various optical recording media such as CD-R, CD-RW, and MO can store a large amount of information and are easily accessible at random, so that they are widely recognized as external storage devices in information processing apparatuses such as computers. It is becoming popular. In such an optical recording medium, it is desired to increase the storage density as the amount of information handled increases.
[0003]
Among various optical recording media, optical recording media (optical discs) such as CD-R, DVD-R, and DVD + R having a recording layer containing an organic dye (also referred to as a dye-containing recording layer) are relatively inexpensive and can be reproduced. Since it is compatible with a dedicated optical recording medium, it is particularly widely used.
As an example, a typical single-sided DVD-R will be described as an optical disk having a dye-containing recording layer. Since DVD + R has almost the same configuration as DVD-R, it is represented in the description of DVD-R.
[0004]
The single-sided DVD-R has a dye-containing recording layer, a reflective layer, and a protective layer covering them in this order on the first transparent disk substrate, and further, with or without an adhesive layer on the protective layer, It is a laminated structure in which a so-called dummy disk having a reflective layer formed as necessary on a second disk substrate (which may be transparent or opaque) is provided, and the recording layer is formed by laser light from one side through the first transparent disk substrate. A mark to be an information signal is formed, and recording / reproduction is performed. The dummy disk may be only a transparent or opaque disk substrate, or a layer other than the reflective layer may be provided.
[0005]
Further, in order to further increase the recording capacity of the optical recording medium, the above single-sided DVD-R is bonded to form an optical recording medium having two recording layers, and laser light is applied to each recording layer from both sides. (I.e., irradiate laser light from one side of the medium and record / reproduce the recording layer closer to this one side, while laser light is also emitted from the other side of the medium) There is also known a double-sided DVD-R which performs irradiation and recording / reproduction of the recording layer closer to the other side.
[0006]
In an optical recording medium such as these single-sided DVD-R and double-sided DVD-R that can irradiate the recording layer with laser light only through the substrate, jitter can be kept low and good reproduction characteristics can be obtained. In addition, in general, a method of forming a mark to be an information signal by irradiating a recording layer with a recording pulse (for example, referred to as a leading pulse and a divided pulse) in which a recording laser is pulsed according to a predetermined recording pulse strategy. It is known (see, for example, Patent Document 1).
[0007]
By the way, in recent years, in an optical recording medium having a plurality of recording layers, the recording / reproducing apparatus is not enlarged and complicated, and a laser is applied from one side to enable continuous reproduction over a plurality of recording layers. It is desired to realize a single-sided incident type optical recording medium (for example, single-sided incident type DVD-R) capable of performing recording / reproducing on these plural recording layers by irradiating light.
[0008]
For this reason, for example, as a single-sided incident type optical recording medium having the following configuration, for example, a dual layer type single-sided incident type DVD-R having two recording layers has been proposed (see, for example, Patent Document 2).
For example, a bonded dual layer type single-sided incidence DVD-R has a first recording layer made of an organic dye capable of optically recording information by irradiation with a recording laser beam on a first translucent substrate. A first reflective layer composed of a semi-transparent reflective film capable of transmitting a part of the reproduction laser beam, an intermediate layer having transparency to the recording laser beam and the reproduction laser beam, and recording The second recording layer is made of an organic dye capable of optically recording information by irradiation with the laser beam for use, the second reflection layer for reflecting the reproduction laser beam, and the second substrate.
[0009]
[Patent Document 1]
JP 2000-187841 A
[Patent Document 2]
Japanese Patent Laid-Open No. 11-066662
[0010]
[Problems to be solved by the invention]
However, in a single-sided incident optical recording medium that records or reproduces information on a plurality of recording layers by irradiating laser light from one side, such as a dual-layer type single-sided incident DVD-R, for example, When a mark that becomes an information signal is formed using a recording pulse strategy similar to that of an optical recording medium that irradiates a recording layer with a laser beam only through a substrate, such as single-sided DVD-R or double-sided DVD-R, There is a problem that jitter is deteriorated.
[0011]
The present invention has been devised in view of such problems, and each recording layer is formed when a mark that becomes an information signal is formed on a plurality of recording layers by irradiating laser light (recording laser) from one side. To provide a recording method and a recording apparatus for an optical recording medium, which can form a mark (record mark) more accurately, reduce jitter of a reproduction signal of each recording layer, and obtain good reproduction characteristics. With the goal.
[0012]
[Means for Solving the Problems]
The gist of the present invention is that a recording laser is irradiated from one side to form a mark having a length nT (n is a natural number of 4 or more and 14 or less, and T is a reference clock period) that is an information signal for a plurality of recording layers. In the recording method of the optical recording medium, the recording laser is irradiated with a length using at least a first pulse for forming the mark start region and a last pulse for forming the mark end region. When forming an nT mark, the mark is formed by changing the position of the leading edge of the first pulse and / or the position of the trailing edge of the last pulse according to the length of the mark. It exists in the recording method of a medium.
[0013]
Further, the gist of the present invention is an optical recording in which a recording laser beam is incident from one side of an optical recording medium having a plurality of recording layers to form a mark having a desired length on each recording layer to record information. In a medium recording apparatus, when the mark is formed by irradiating a pulsed recording laser beam through another recording layer, a start end region of the mark is formed according to the length of the mark In the recording apparatus of the optical recording medium, the pulse width of the first pulse and / or the pulse width of the last pulse for forming the end region of the mark is changed.
[0014]
Further, the gist of the present invention is an optical recording in which recording laser light is incident from one side of an optical recording medium having a plurality of recording layers to form a mark having a desired length on each recording layer and information is recorded. In the recording apparatus for a medium, when the mark is formed by irradiating a pulsed recording laser beam without passing through another recording layer, a start end region of the mark is formed according to the length of the mark The recording apparatus of the optical recording medium is configured to change a pulse width of the first pulse for the purpose and / or a pulse width of the last pulse for forming the end region of the mark.
[0015]
According to the present invention, when a mark that becomes an information signal is formed on a plurality of recording layers by irradiating laser light from one side, a mark (recording mark) can be accurately formed by each recording layer. Therefore, the jitter of the reproduction signal of each recording layer can be kept low, and good reproduction characteristics can be obtained. Furthermore, according to the present invention, it is possible to appropriately suppress the excessive spread of the mark, and thus it is possible to suppress the leakage of the signal to the adjacent track.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a recording method and a recording apparatus for an optical recording medium according to an embodiment of the present invention will be described with reference to FIGS.
The recording method of the optical recording medium according to the present embodiment has, for example, a plurality of recording layers, and can record or reproduce information on each recording layer by irradiating light (laser light) from one side. It is preferably used for recording information (data) on a single-sided incident type optical recording medium (write-once type optical recording medium). In particular, when applied to an optical recording medium having a dye-containing recording layer such as a single-sided incident DVD-R, the effect is higher.
[0017]
In the present embodiment, as a single-sided incident type optical recording medium (single-sided incident type DVD-R), for example, a dual layer type single-sided incident type DVD-R having two recording layers (dual layer medium, single-sided double-layer DVD-R, A single-sided dual-layer DVD recordable disc) will be described as an example.
(1) Structure of optical recording medium
First, two types of optical recording media (optical discs) having different laminated structures will be described as optical recording media according to the present embodiment.
(A) Type 1
FIG. 1 is a schematic cross-sectional view showing an optical recording medium (type 1, laminated single-sided incidence type optical recording medium) according to the present embodiment.
[0018]
As shown in FIG. 1, a type 1 optical recording medium according to the present embodiment is formed on a disk-shaped transparent (light transmissive) first substrate (first substrate, first light transmissive substrate) 1. A first recording layer containing a dye (first recording layer, first dye-containing recording layer) 2, a semitransparent first reflective layer (semitransparent reflective layer) 3, an intermediate resin layer (intermediate layer) 4, and a dye A second recording layer (second recording layer, second dye-containing recording layer) 5, a second reflective layer 6, an adhesive layer 7, and a second substrate (second substrate) 8 are included in this order. The light beam is irradiated from the first substrate 1 side, and recording or reproduction is performed.
[0019]
In the present embodiment, being transparent (having light transmission) means being transparent (having light transmission) with respect to a light beam used for recording or reproduction on an optical recording medium. Further, the transparent (light-transmitting) layer includes a layer that absorbs a light beam used for recording or reproduction to some extent. For example, if the wavelength of the light beam used for recording or reproduction is 50% or more, preferably 60% or more, it is substantially light transmissive (transparent).
[0020]
Concavities and convexities (lands and grooves) are formed on the first substrate 1 and the intermediate resin layer 4, respectively, and constitute recording tracks. The recording track may be either a convex portion or a concave portion, but the recording track 11 on the first substrate 1 is preferably constituted by a groove portion of the first substrate 1, that is, a convex portion with respect to the light incident direction. The recording track 12 on the resin layer 4 is preferably composed of a groove in the intermediate resin layer 4, that is, a convex portion with respect to the light incident direction. Unless otherwise specified, in this embodiment, the unevenness is defined with respect to the incident direction of light used for recording or reproduction. In addition, it may have uneven pits such as land prepits as necessary.
[0021]
Next, each layer will be described.
(A) About the first substrate 1
The first substrate 1 is preferably transparent and has excellent optical properties such as a low birefringence. The refractive index of the first substrate 1 (refractive index with respect to the wavelength of recording light or reproducing light) is usually 1.40 or more, preferably 1.45 or more. However, it is usually 1.70 or less, preferably 1.65 or less. Moreover, it is desirable that the moldability is excellent, such as easy injection molding. Furthermore, it is desirable that the hygroscopicity is small because warpage can be reduced.
[0022]
Furthermore, it is desirable to provide shape stability so that the optical recording medium has a certain degree of rigidity. However, as long as the second substrate 8 has sufficient shape stability, the first substrate 1 may not have high shape stability.
Examples of such materials include those made of resins such as acrylic resins, methacrylic resins, polycarbonate resins, polyolefin resins (particularly amorphous polyolefins), polyester resins, polystyrene resins, epoxy resins, and the like. Can be used. Or the 1st board | substrate 1 may consist of a several layer, for example, what provided the resin layer which consists of radiation curable resin, such as photocuring resin, on base | substrates, such as glass and resin, can be used. Radiation is a general term for light (ultraviolet rays, visible rays, infrared rays, etc.), electron beams, and the like.
[0023]
Polycarbonate is preferable from the viewpoints of high productivity such as optical characteristics and moldability, cost, low hygroscopicity, and shape stability. Amorphous polyolefin is preferred from the standpoint of chemical resistance and low hygroscopicity. Moreover, a glass substrate is preferable from the viewpoint of high-speed response.
The first substrate 1 is preferably thin, and usually the thickness is preferably 2 mm or less, more preferably 1 mm or less. This is because the coma aberration tends to be smaller as the distance between the objective lens and the recording layer is smaller and the substrate is thinner, and the recording density is easily increased. However, in order to obtain sufficient optical properties, hygroscopicity, moldability, and shape stability, a certain amount of thickness is necessary, and is usually preferably 10 μm or more, more preferably 30 μm or more.
[0024]
In the present optical recording medium, it is desirable to appropriately adjust the distance between the objective lens and both recording layers in order to perform good recording and reproduction on both the first recording layer 2 and the second recording layer 5. For example, it is preferable to set the focal point of the objective lens at a substantially middle point between the two recording layers because the both recording layers can be easily accessed.
More specifically, in DVD-ROM and DVD-R systems, the distance between the objective lens and the recording layer is adjusted to be optimal when the substrate thickness is 0.6 mm.
[0025]
Accordingly, in the case of DVD-ROM compatibility in this layer configuration, the thickness of the first substrate 1 is most preferably a thickness obtained by subtracting one half of the thickness of the intermediate resin layer 4 from 0.6 mm. preferable. At this time, the substantially middle point between both recording layers is about 0.6 mm, and it is easy to apply focus servo to both recording layers.
When there are other layers such as a buffer layer and a protective layer between the second recording layer 5 and the translucent reflective layer 3, the thickness of these layers and the intermediate resin layer 4 is 2 from the thickness of 0.6 mm. Most preferably, the thickness is reduced by a factor of one.
[0026]
The first substrate 1 is provided with irregularities in a spiral shape or a concentric shape to form grooves and lands. Normally, information is recorded / reproduced in / from the first recording layer 2 using such grooves and / or lands as recording tracks. In the case of a so-called DVD-R disc in which recording / reproduction is performed by condensing a laser having a wavelength of 650 nm with an objective lens having a numerical aperture of 0.6 to 0.65, the first recording layer 2 is usually formed by coating. It is thick and suitable for recording and playback.
[0027]
Usually, the groove width is about 50 to 500 nm, and the groove depth is about 10 to 250 nm. When the recording track is spiral, the track pitch is preferably about 0.1 to 2.0 μm.
From the viewpoint of cost, the substrate having such irregularities is preferably manufactured by injection molding from a stamper having irregularities. When a resin layer made of a radiation curable resin such as a photocurable resin is provided on a substrate such as glass, irregularities such as recording tracks may be formed on the resin layer.
(B) About the first recording layer 2
The dye used for the first recording layer 2 usually has the same sensitivity as the dye used for a single-sided recording medium (for example, CD-R, DVD-R, DVD + R).
[0028]
In order to realize good recording / reproducing characteristics, it is desirable that the dye has a low heat generation and a high refractive index.
Here, the refractive index (refractive index with respect to the wavelength of recording light or reproducing light) of the dye used for the first recording layer 2 is usually 1.00 or more, preferably 1.50 or more. However, it is usually 3.00 or less.
[0029]
Further, the extinction coefficient of the dye used for the first recording layer 2 (extinction coefficient with respect to the wavelength of recording light or reproducing light) is usually 0.50 or less, preferably 0.30 or less. If the extinction coefficient is too large, the absorption by the dye-containing recording layer becomes too large, and the reflectance becomes low. However, in order to perform recording, it is preferable that there is some absorption, and there is no particular lower limit, but it is usually 0.001 or more.
[0030]
Further, in the combination of the first recording layer 2 and the translucent reflective layer 3, it is desirable that the reflection, transmission and absorption of light be in an appropriate range. The recording sensitivity can be increased and the thermal interference during recording can be reduced.
Examples of such organic dye materials include macrocyclic azaannulene dyes (phthalocyanine dyes, naphthalocyanine dyes, porphyrin dyes, etc.), pyromethene dyes, polymethine dyes (cyanine dyes, merocyanine dyes, squarylium dyes, etc.), anthraquinone dyes, Examples include azulenium dyes, metal-containing azo dyes, and metal-containing indoaniline dyes.
[0031]
Among the above-mentioned various organic dyes, metal-containing azo dyes are preferable because of excellent recording sensitivity and durability and light resistance. In particular, the following general formula (I) or (II)
[0032]
[Chemical 1]

[0033]
(Ring A ¹ And A ² Are nitrogen-containing aromatic heterocycles each independently having a substituent, and ring B ¹ And B ² Are each independently an aromatic ring optionally having a substituent. X is a C1-C6 alkyl group substituted with at least two fluorine atoms. ) Is preferred.
The recording layer of the present optical recording medium (hereinafter referred to as “recording layer” refers to both the first recording layer 1 and the second recording layer 2 unless otherwise specified). The organic dye to be used is preferably a dye compound having a maximum absorption wavelength λmax in the visible light to near infrared region of about 350 to 900 nm and suitable for recording with a blue to near microwave laser. A near-infrared laser having a wavelength of about 770 to 830 nm (typically 780 nm, 830 nm, etc.) used for a CD-R or a red laser having a wavelength of about 620 to 690 nm (typically used for a DVD-R) 635 nm, 650 nm, 680 nm, etc.), or a dye suitable for recording with a so-called blue laser having a wavelength of 410 nm or 515 nm is more preferable.
[0034]
One kind of dye may be used, or two or more kinds of the same kind or different kinds may be used in combination. Furthermore, it is also possible to use an optical recording medium corresponding to recording with laser light in a plurality of wavelength regions by using a combination of dyes suitable for recording in each of the recording light with the plurality of wavelengths.
In addition, the recording layer has a transition metal chelate compound (for example, acetylacetonate chelate, bisphenyldithiol, salicylaldehyde oxime, bisdithio-α-diketone, etc.) as a singlet oxygen quencher to improve the stability and light resistance of the recording layer. ) And the like, and a recording sensitivity improver such as a metal compound may be contained for improving the recording sensitivity.
[0035]
Here, the metal compound refers to a compound in which a metal such as a transition metal is contained in the form of atoms, ions, clusters, etc., for example, ethylenediamine complex, azomethine complex, phenylhydroxyamine complex, phenanthroline complex. And organometallic compounds such as dihydroxyazobenzene complex, dioxime complex, nitrosoaminophenol complex, pyridyltriazine complex, acetylacetonate complex, metallocene complex, and porphyrin complex. Although it does not specifically limit as a metal atom, It is preferable that it is a transition metal.
[0036]
Furthermore, a binder, a leveling agent, an antifoaming agent, and the like can be used in combination in the recording layer of the optical recording medium as necessary. 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.
[0037]
The film thickness of the recording layer varies depending on the recording method and the like, and is not particularly limited. However, in order to obtain a sufficient degree of modulation, it is usually preferably 5 nm or more, more preferably 10 nm or more, Especially preferably, it is 20 nm or more. However, in the present optical recording medium, since it is not necessary to be too thick in order to transmit light moderately, it is usually 3 μm or less, preferably 1 μm or less, more preferably 200 nm or less. The film thickness of the recording layer is usually different between the groove part and the land part, but in this optical recording medium, the film thickness of the recording layer is the film thickness in the groove part of the substrate.
[0038]
Examples of the method for forming the recording layer include vacuum film forming methods, sputtering methods, doctor blade methods, cast methods, spin coating methods, dipping methods, and the like, but from the viewpoint of mass productivity and cost, A spin coating method is preferred. From the viewpoint that a recording layer having a uniform thickness can be obtained, the vacuum vapor deposition method is preferable to the coating method.
[0039]
In the case of film formation by spin coating, the rotation speed is preferably 10 to 15000 rpm, and after spin coating, treatment such as heating or application 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 2-hydroxyisobutyrate.
[0040]
In the case of the vacuum vapor deposition method, for example, an organic dye and recording layer components such as various additives as necessary are put in a crucible installed in a vacuum vessel, and the inside of the vacuum vessel is filled with an appropriate vacuum pump. ^-2 -10 ^-5 After evacuating to about Pa, the crucible is heated to evaporate the recording layer components and vapor deposited on the substrate placed facing the crucible to form the recording layer.
(C) About the first reflective layer 3
The first reflective layer 3 is a reflective layer having a certain degree of light transmittance. That is, the reflective layer has a small absorption of recording / reproducing light, a light transmittance of 40% or more, and an appropriate light reflectance (usually 30% or more). The first reflective layer 3 is also referred to as a translucent reflective layer 3. For example, an appropriate transmittance can be provided by providing a thin metal with high reflectivity. Moreover, it is desirable that there is some degree of corrosion resistance. Further, it is desirable that the first recording layer 2 is blocked so that the first recording layer 2 is not affected by the seepage of the upper layer (here, the intermediate resin layer 4) of the first reflective layer 3.
[0041]
In order to ensure high transmittance, the thickness of the first reflective layer 3 is usually preferably 50 nm or less. More preferably, it is 30 nm or less. More preferably, it is 25 nm or less. However, since the first recording layer 2 is not affected by the upper layer of the first reflective layer 3, a certain thickness is required, and usually 3 nm or more. More preferably, it is 5 nm or more.
[0042]
As the material of the first reflective layer 3, a material having a reasonably high reflectance at the wavelength of the reproduction light, for example, Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Pd, Mg, Se, Hf , V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Zn, Cd, Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi, and rare earth metals and semi-metals It is possible to use a metal alone or as an alloy. Among these, Au, Al, and Ag have high reflectivity and are suitable as materials for the first reflective layer 3. In addition to these as main components, other components may be included.
[0043]
Among these, those containing Ag as a main component are particularly preferable from the viewpoint of low cost and high reflectance. Here, the main component means one having a content of 50% or more.
Since the first reflective layer 3 has a small film thickness and large crystal grains in the film cause reproduction noise, it is preferable to use a material with small crystal grains. Since pure silver tends to have large crystal grains, Ag is preferably used as an alloy.
[0044]
Among these, it is preferable to contain 0.1 to 15 atomic% of at least one element selected from the group consisting of Ag, Ti, Zn, Cu, Pd, Au, and rare earth metals. When two or more of Ti, Zn, Cu, Pd, Au, and rare earth metal are included, each may be 0.1 to 15 atomic%, but the total of these is preferably 0.1 to 15 atomic%. .
[0045]
A particularly preferable alloy composition contains 0.1 to 15 atomic% of at least one element selected from the group consisting of Ti, Zn, Cu, Pd, and Au, containing Ag as a main component, and at least one rare earth element. Is contained in an amount of 0.1 to 15 atomic%. Of the rare earth metals, neodymium is particularly preferred. Specifically, AgPdCu, AgCuAu, AgCuAuNd, AgCuNd, and the like.
[0046]
As the first reflective layer 3, a layer made only of Au is suitable because it has small crystal grains and is excellent in corrosion resistance. However, it is more expensive than Ag alloy.
It is also possible to use a layer made of Si as the first reflective layer 3.
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.
[0047]
Examples of the method for forming the first reflective layer 3 include sputtering, ion plating, chemical vapor deposition, and vacuum vapor deposition. Further, between the first substrate 1 and the first recording layer 2 and / or between the first recording layer 2 and the first reflective layer 3, the reflectance is improved, the recording characteristics are improved, and the adhesion is improved. For example, a known inorganic or organic intermediate layer or adhesive layer may be provided.
(D) About the intermediate resin layer 4
The intermediate resin layer 4 needs to be transparent and can be formed with grooves and pits by unevenness. Further, it is preferable that the adhesive strength is high and the shrinkage rate at the time of curing and bonding is small, the shape stability of the medium is high.
[0048]
The refractive index (refractive index with respect to the wavelength of recording light or reproducing light) of the intermediate resin layer 4 is usually 1.40 or more, preferably 1.45 or more. However, it is usually 1.70 or less, preferably 1.65 or less.
The intermediate resin layer 4 is preferably made of a material that does not damage the second recording layer 5. However, since the intermediate resin layer 4 is usually made of a resin, it is easily compatible with the second recording layer 5. In order to prevent this and prevent damage, it is desirable to provide a buffer layer described later between the two layers.
[0049]
Furthermore, the intermediate resin layer 4 is preferably made of a material that does not damage the first reflective layer 3. However, in order to suppress damage, a buffer layer described later can be provided between both layers.
In the present optical recording medium, it is preferable to control the film thickness of the intermediate resin layer 4 accurately. The film thickness of the intermediate resin layer 4 is usually preferably 5 μm or more. In order to separately apply focus servo to the two recording layers, it is necessary to have a certain distance between the two recording layers. Although it depends on the focus servo mechanism, 5 μm or more, preferably 10 μm or more is required.
[0050]
In general, the higher the numerical aperture of the objective lens, the smaller the distance tends to be. However, if it is too thick, it takes time to adjust the focus servo to the two recording layers, and the moving distance of the objective lens becomes long, which is not preferable. Moreover, since there are problems such as requiring time for curing and lowering productivity, the thickness is usually preferably 100 μm or less.
The intermediate resin layer 4 is provided with irregularities in a spiral shape or concentric shape to form grooves and lands. Normally, information is recorded / reproduced in / from the second recording layer 5 using such grooves and / or lands as recording tracks. Usually, since the second recording layer 5 is formed by coating, it becomes thick at the groove and is suitable for recording and reproduction. Usually, the groove width is about 200 to 500 nm, and the groove depth is about 120 to 250 nm. When the recording track is spiral, the track pitch is preferably about 0.1 to 2.0 μm.
[0051]
From the viewpoint of cost, such irregularities are preferably produced by transferring and curing from a resin stamper having irregularities to a curable resin such as a photocurable resin. Hereinafter, such a method may be referred to as a 2P method (Photo Polymerization method).
Examples of the material of the intermediate resin layer 4 include a thermoplastic resin, a thermosetting resin, an electron beam curable resin, an ultraviolet curable resin (including a delayed curable type), and the like.
[0052]
A thermoplastic resin, a thermosetting resin, or the like can be formed by dissolving in an appropriate solvent to prepare a coating solution, coating it, and drying (heating). The ultraviolet curable resin can be formed by preparing a coating solution as it is or by dissolving it in a suitable solvent, and then applying the coating solution and curing it by irradiating with ultraviolet light. There are various types of ultraviolet curable resins, and any of them can be used as long as it is transparent. These materials may be used alone or in combination, and may be used not only as a single layer but also as a multilayer film.
[0053]
As a coating method, a method such as a spin coating method or a casting method is used as in the recording layer, and among these, the spin coating method is preferable. Alternatively, a resin having a high viscosity can be formed by screen printing or the like. It is preferable to use an ultraviolet curable resin that is liquid at 20 to 40 ° C. because it can be applied without using a solvent. The viscosity is preferably adjusted to 20 to 1000 mPa · s.
[0054]
As the ultraviolet curable adhesive, there are a radical ultraviolet curable adhesive and a cationic ultraviolet curable adhesive, both of which can be used.
As the radical ultraviolet curable adhesive, all known compositions can be used, and a composition containing an ultraviolet curable compound and a photopolymerization initiator as essential components is used. As the ultraviolet curable compound, monofunctional (meth) acrylate or polyfunctional (meth) acrylate can be used as the polymerizable monomer component. These can be used alone or in combination of two or more. Here, in the present invention, acrylate and methacrylate are collectively referred to as (meth) acrylate.
[0055]
Examples of polymerizable monomers that can be used in the present optical recording medium include the following. Examples of the monofunctional (meth) acrylate include methyl, ethyl, propyl, butyl, amyl, 2-ethylhexyl, octyl, nonyl, dodecyl, hexadecyl, octadecyl, cyclohexyl, benzyl, methoxyethyl, butoxyethyl, phenoxyethyl, Nonylphenoxyethyl, tetrahydrofurfuryl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-chloro-2-hydroxypropyl, dimethylaminoethyl, diethylaminoethyl, nonylphenoxyethyl tetrahydrofurfuryl, caprolactone modified tetrahydrofurfuryl, isobornyl , (Meth) acrylate having a group such as dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl and the like.
[0056]
Examples of the polyfunctional (meth) acrylate include 1,3-butylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, and 1,6-hexanediol. Di (meth) such as neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, tricyclodecane dimethanol, ethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol Di (meth) acrylate of diol obtained by adding 4 mol or more of ethylene oxide or propylene oxide to 1 mol of acrylate, tris (2-hydroxyethyl) isocyanurate di (meth) acrylate, neopentyl glycol Diol di (meth) acrylate obtained by adding 2 mol of ethylene oxide or propylene oxide to 1 mol of bisphenol A, triol obtained by adding 3 mol or more of ethylene oxide or propylene oxide to 1 mol of trimethylolpropane Di or tri (meth) acrylate, di (meth) acrylate of diol obtained by adding 4 mol or more of ethylene oxide or propylene oxide to 1 mol of bisphenol A, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) Acrylate, poly (meth) acrylate of dipentaerythritol, ethylene oxide modified phosphoric acid (meth) acrylate, ethylene oxide modified alkylated phosphoric acid (meth) acrylate, etc. It is.
[0057]
Moreover, what can be used together with the polymerizable monomer includes polyester (meth) acrylate, polyether (meth) acrylate, epoxy (meth) acrylate, urethane (meth) acrylate and the like as polymerizable oligomers.
Furthermore, as the photopolymerization initiator used in the present optical recording medium, any known one that can cure an ultraviolet curable compound represented by a polymerizable oligomer and / or a polymerizable monomer can be used. As the photopolymerization initiator, a molecular cleavage type or a hydrogen abstraction type is suitable for the optical recording medium.
[0058]
Examples of such include benzoin isobutyl ether, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, benzyl, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-benzyl-2-dimethylamino-1- ( 4-morpholinophenyl) -butan-1-one, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, etc. are preferably used, and other molecular cleavage types 1-hydroxycyclohexyl phenyl ketone, benzoin ethyl ether, benzyldimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methyl Propan-1-one and -Methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one or the like may be used in combination, and further a hydrogen abstraction type photopolymerization initiator, benzophenone, 4-phenylbenzophenone, isophthalphenone 4-benzoyl-4′-methyl-diphenyl sulfide and the like can be used in combination.
[0059]
Examples of sensitizers for photopolymerization initiators include trimethylamine, methyldimethanolamine, triethanolamine, p-diethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, N, N-dimethylbenzyl. An amine that does not cause an addition reaction with the polymerizable component, such as an amine and 4,4′-bis (diethylamino) benzophenone, can also be used in combination. Of course, it is preferable to select and use the photopolymerization initiator and the sensitizer that are excellent in solubility in the ultraviolet curable compound and do not inhibit the ultraviolet transmittance.
[0060]
Further, as the cationic ultraviolet curable adhesive, all known compositions can be used, and an epoxy resin containing a cationic polymerization type photoinitiator corresponds to this. Examples of cationic polymerization type photoinitiators include sulfonium salts, iodonium salts, and diazonium salts.
An example of an iodonium salt is as follows. Diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, diphenyliodonium tetrafluoroborate, diphenyliodonium tetrakis (pentafluorophenyl) borate, bis (dodecylphenyl) iodonium hexafluorophosphate, bis (dodecylphenyl) iodonium hexafluoroantimonate, Bis (dodecylphenyl) iodonium tetrafluoroborate, bis (dodecylphenyl) iodonium tetrakis (pentafluorophenyl) borate, 4-methylphenyl-4- (1-methylethyl) phenyliodonium hexafluorophosphate, 4-methylphenyl-4- (1-Methylethyl) phenyliodonium hexafluoroa Chimoneto, 4-methylphenyl-4- (1-methylethyl) phenyl iodonium tetrafluoroborate, 4-methylphenyl-4- (1-methylethyl) phenyl iodonium tetrakis (pentafluorophenyl) borate, and the like.
[0061]
The epoxy resin can be any of various types such as bisphenol A-epichlorohydrin type, alicyclic epoxy, long chain aliphatic type, brominated epoxy resin, glycidyl ester type, glycidyl ether type, and heterocyclic type. It doesn't matter.
As the epoxy resin, it is preferable to use an epoxy resin having a low free chlorine and chlorine ion content so as not to damage the reflective layer. The amount of chlorine is preferably 1% by weight or less, more preferably 0.5% by weight or less.
[0062]
The ratio of the cationic polymerization type photoinitiator per 100 parts by weight of the cationic ultraviolet curable resin is usually 0.1 to 20 parts by weight, preferably 0.2 to 5 parts by weight. A known photosensitizer can be used in combination in order to use the near-ultraviolet region and the visible region of the ultraviolet light source more effectively. Examples of the photosensitizer at this time include anthracene, phenothiazine, benzylmethyl ketal, benzophenone, and acetophenone.
[0063]
In addition, UV curable adhesives include, as necessary, other additives such as thermal polymerization inhibitors, antioxidants typified by hindered phenols, hindered amines, phosphites, plasticizers and epoxy silanes, mercapto. Silane coupling agents represented by silane, (meth) acrylic silane and the like can also be blended for the purpose of improving various properties. These are selected from those having excellent solubility in ultraviolet curable compounds and those that do not impair ultraviolet transparency.
(E) Second recording layer 5
The dye used for the second recording layer 5 is usually more sensitive than the dye used for a single-sided recording medium (for example, CD-R, DVD-R, DVD + R). In the present optical recording medium, since the power of the incident light beam decreases due to the presence of the first recording layer 2 and the semitransparent reflective layer 3, etc., it is necessary to have particularly high sensitivity in order to record at about half the power. It is.
[0064]
In order to realize good recording / reproducing characteristics, it is desirable that the dye has a low heat generation and a high refractive index.
Here, the refractive index of the dye used for the second recording layer 5 (refractive index with respect to the wavelength of recording light or reproducing light) is usually 1.00 or more, preferably 1.50 or more. However, it is usually 3.00 or less.
[0065]
Further, the extinction coefficient of the dye used for the second recording layer 5 (extinction coefficient with respect to the wavelength of recording light or reproducing light) is usually 0.50 or less, preferably 0.30 or less. If the extinction coefficient is too large, the absorption by the dye recording layer becomes too large and the reflectance becomes low. However, in order to perform recording, it is preferable that there is some absorption, and there is no particular lower limit, but it is usually 0.001 or more.
[0066]
Further, in the combination of the second recording layer 5 and the reflective layer 6, it is desirable that the reflection and absorption of light be in an appropriate range. The recording sensitivity can be increased and the thermal interference during recording can be reduced.
Since the material of the second recording layer 5, the film forming method, and the like are described in substantially the same manner as in the first recording layer 2, only different points will be described.
[0067]
The film thickness of the second recording layer 5 is not particularly limited because it varies depending on the recording method and the like. However, in order to obtain a sufficient degree of modulation, it is usually preferably 10 nm or more, more preferably 30 nm or more. And particularly preferably 50 nm or more. However, since it is not necessary to be too thick in order to obtain an appropriate reflectance, it is usually 3 μm or less, preferably 1 μm or less, more preferably 200 nm or less. Here, the film thickness of the second recording layer 5 usually refers to the film thickness in the thick film portion.
[0068]
The materials used for the first recording layer 2 and the second recording layer 5 may be the same or different.
(F) About the second reflective layer 6
The second reflective layer 6 needs to have a high reflectance. Moreover, it is desirable that it is highly durable.
[0069]
In order to ensure a high reflectance, the thickness of the second reflective layer 6 is usually preferably 20 nm or more. More preferably, it is 30 nm or more. More preferably, it is 50 nm or more. However, in order to shorten the production tact time and reduce the cost, it is preferable to be thin to some extent, and is usually set to 400 nm or less. More preferably, it is set to 300 nm or less.
[0070]
As a material of the second reflective layer 6, 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, and Pd is used alone or in an alloy. Can be used. Among these, Au, Al, and Ag have high reflectivity and are suitable as materials for the second reflective layer 6. In addition to these as main components, the following components may be included as other components. Examples of other components include Mg, Se, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Cu, Zn, Cd, Ga, In, Si, Ge, Te, Pb Mention may be made of metals and metalloids such as Po, Sn, Bi and rare earth metals.
[0071]
Among them, those containing Ag as a main component are particularly preferred because they are low in cost, easily exhibit high reflectivity, and when a print receiving layer described later is provided, a white and beautiful ground color can be obtained. Here, the main component means one having a content of 50% or more.
In order to ensure high durability (high corrosion resistance), the second reflective layer 6 is preferably used as an alloy rather than pure silver.
[0072]
Among these, it is preferable to contain 0.1 to 15 atomic% of at least one element selected from the group consisting of Ag, Ti, Zn, Cu, Pd, Au, and rare earth metals. When two or more of Ti, Zn, Cu, Pd, Au, and rare earth metal are included, each may be 0.1 to 15 atomic%, but the total of these is preferably 0.1 to 15 atomic%. .
[0073]
A particularly preferable alloy composition contains 0.1 to 15 atomic% of at least one element selected from the group consisting of Ti, Zn, Cu, Pd, and Au, containing Ag as a main component, and at least one rare earth element. Is contained in an amount of 0.1 to 15 atomic%. Of the rare earth metals, neodymium is particularly preferred. Specifically, AgPdCu, AgCuAu, AgCuAuNd, AgCuNd, and the like.
[0074]
As the second reflective layer 6, a layer made only of Au is preferable because of its high durability (high corrosion resistance). However, it is more expensive than Ag alloy.
A multilayer film can be formed by alternately stacking a low refractive index thin film and a high refractive index thin film using a material other than metal, and can be used as the second reflective layer 6.
Examples of the method for forming the second reflective layer 6 include sputtering, ion plating, chemical vapor deposition, and vacuum vapor deposition. In addition, a known inorganic or organic intermediate layer or adhesive layer may be provided above and below the second reflective layer 6 in order to improve reflectivity, improve recording characteristics, and improve adhesion.
(G) About adhesive layer 7
The adhesive layer 7 does not need to be transparent, but it is preferable that the adhesive strength is high and the shrinkage rate at the time of curing and bonding is small, so that the medium has high shape stability.
[0075]
The adhesive layer 7 is preferably made of a material that does not damage the second reflective layer 6. However, a known inorganic or organic protective layer may be provided between both layers in order to suppress damage.
In the present optical recording medium, the film thickness of the adhesive layer 7 is usually preferably 2 μm or more. In order to obtain a predetermined adhesive strength, a certain film thickness is required. More preferably, it is 5 μm or more. However, in order to make the optical recording medium as thin as possible, and there is a problem that it takes time for curing and productivity is lowered.
[0076]
The material of the adhesive layer 7 can be the same as the material of the intermediate resin layer 4, and a pressure-sensitive double-sided tape or the like can also be used. The adhesive layer 7 can be formed by sandwiching and pressing a pressure-sensitive double-sided tape between the reflective layer 6 and the second substrate 8.
(H) About the second substrate 8
The second substrate 8 preferably has shape stability so that the optical recording medium has a certain degree of rigidity. That is, it is preferable that mechanical stability is high and rigidity is large. Moreover, it is desirable that the adhesiveness with the adhesive layer 7 is high.
[0077]
As described above, when the first substrate 1 does not have sufficient shape stability, the second substrate 8 needs to have particularly high shape stability. In this respect, it is desirable that the hygroscopicity is small. However, the second substrate 8 does not need to be transparent. The second substrate 8 may be a mirror substrate, and it is not necessary to form irregularities, so that the transferability by injection molding is not necessarily good.
[0078]
As such a material, the same material as that which can be used for the first substrate 1 can be used. For example, an Al alloy substrate such as an Al—Mg alloy containing Al as a main component, or an Mg alloy as a main component, for example. An Mg alloy substrate such as an Mg—Zn alloy, a substrate made of any of silicon, titanium, and ceramics, a substrate that combines them, and the like can be used.
[0079]
Polycarbonate is preferred from the viewpoints of high productivity such as moldability, cost, low hygroscopicity, and shape stability. Amorphous polyolefin is preferred from the standpoint of chemical resistance and low hygroscopicity. Moreover, a glass substrate is preferable from the viewpoint of high-speed response.
In order to give the optical recording medium sufficient rigidity, the second substrate 8 is preferably thick to some extent, and the thickness is preferably 0.3 mm or more. However, the thinner one is advantageous for thinning the recording / reproducing apparatus, and it is preferably 3 mm or less. More preferably, it is 1.5 mm or less.
[0080]
The second substrate 8 may be a mirror substrate having no irregularities, but is preferably manufactured by injection molding from the viewpoint of ease of production.
As an example of a preferable combination of the first substrate 1 and the second substrate 8, the first substrate 1 and the second substrate 8 are made of the same material and have the same thickness. Since the rigidity is equal and balanced, it is preferable that the medium is difficult to be deformed against environmental changes. In this case, it is preferable that the degree and direction of deformation when the environment changes are the same for both substrates.
[0081]
As an example of another preferable combination, the first substrate 1 is as thin as about 0.1 mm, and the second substrate 8 is as thick as about 1.1 mm. The objective lens is preferable because it easily approaches the recording layer and easily increases the recording density. At this time, the first substrate 1 may be in the form of a sheet.
(I) Other layers
In the above laminated structure, any other layer may be sandwiched as necessary. Alternatively, any other layer may be provided on the outermost surface of the medium. Specifically, an intermediate layer is provided between the first reflective layer 3 and the intermediate resin layer 4, between the intermediate resin layer 4 and the second recording layer 5, between the second reflective layer 6 and the adhesive layer 7, and the like. A buffer layer may be provided.
[0082]
The buffer layer prevents the two layers from mixing and prevents compatibility. The buffer layer may also serve other functions than preventing the mixing phenomenon. Further, another intermediate layer may be interposed as required.
The material of the buffer layer is not compatible with the second recording layer 5 or the intermediate resin layer 4 and needs to have a certain degree of light transmittance, but known inorganic and organic materials can be used. In view of characteristics, an inorganic material is preferably used. For example, (1) metal or semiconductor, (2) metal or semiconductor oxide, nitride, sulfide, oxysulfide, fluoride or carbide, or (3) amorphous carbon is used. Among them, a layer made of a substantially transparent dielectric or a very thin metal layer (including an alloy) is preferable.
[0083]
Specifically, silicon oxide, particularly silicon dioxide, oxides such as zinc oxide, cerium oxide, yttrium oxide; sulfides such as zinc sulfide and yttrium sulfide; nitrides such as silicon nitride; silicon carbide; oxide and sulfur A mixture thereof (oxysulfide); and alloys described later are suitable. Further, a mixture of about 30:70 to 90:10 (weight ratio) of silicon oxide and zinc sulfide is also suitable. A mixture of sulfur, yttrium dioxide and zinc oxide (Y ₂ O ₂ S-ZnO) is also suitable
As the metal or alloy, silver or one containing 0.1 to 15 atomic% of at least one element selected from the group consisting of titanium, zinc, copper, palladium, and gold, which is mainly composed of silver, is preferable. is there. Further, those containing silver as a main component and containing at least one rare earth element in an amount of 0.1 to 15 atomic% are also suitable. As the rare earth, neodymium, praseodymium, cerium and the like are suitable.
[0084]
In addition, a resin layer may be used as long as it does not dissolve the dye in the recording layer when the buffer layer is produced. In particular, a polymer film that can be produced by vacuum deposition or CVD is useful.
The thickness of the buffer layer is preferably 2 nm or more, more preferably 5 nm or more. If the thickness of the buffer layer is excessively thin, there is a possibility that the prevention of the above mixing phenomenon will be insufficient. However, it is preferably 2000 nm or less, more preferably 500 nm or less. If the buffer layer is excessively thick, it is not only necessary for preventing mixing but also may reduce light transmittance. In the case of a layer made of an inorganic material, it takes a long time to form a film, and the productivity may be lowered or the film stress may be increased. In particular, in the case of a metal, about 20 nm or less is preferable because the light transmittance is excessively lowered.
[0085]
A protective layer may be provided to protect the recording layer and the reflective layer. The material of the protective layer is not particularly limited as long as it can protect the recording layer and the reflective layer from external force. Examples of the material of the organic substance include a thermoplastic resin, a thermosetting resin, an electron beam curable resin, and an ultraviolet curable resin. Moreover, as an inorganic substance, silicon oxide, silicon nitride, MgF ₂ , SnO ₂ Etc.
[0086]
A thermoplastic resin, a thermosetting resin, etc. can be formed by dissolving in an appropriate solvent to prepare a coating solution, and applying and drying the coating solution. The ultraviolet curable resin can be formed by preparing a coating solution as it is or by dissolving it in a suitable solvent, and then applying the coating solution and curing it by irradiation with UV light. As the ultraviolet 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 not only as a single layer but also as a multilayer film.
[0087]
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 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 1 to 50 μm in the present optical recording medium.
[0088]
Furthermore, the above-mentioned optical recording medium may be provided with a print receiving layer that can be written (printed) on a surface other than the recording / reproducing light incident surface by various printers such as ink jet and thermal transfer, or various writing tools, if necessary. May be provided.
Alternatively, a recording layer may be provided in addition to the main layer configuration, and the number of recording layers may be three or more. Alternatively, two optical recording media having this layer structure and two first recording layers 21 may be bonded to form a larger capacity medium having four recording layers.
(B) Type 2
FIG. 2 is a schematic cross-sectional view showing the optical recording medium (type 2) according to the present embodiment.
[0089]
As shown in FIG. 2, the type 2 optical recording medium (bonded single-sided incident optical recording medium) according to this embodiment is a disc-shaped transparent (light transmissive) first substrate (first optical recording medium). A first recording layer (first recording layer, first dye-containing recording layer) 22 containing a dye and a translucent first reflecting layer (semi-transparent reflecting layer) 23 on a substrate, a first light transmitting substrate) 21. , Transparent adhesive layer (intermediate layer) 24, buffer layer 28, second recording layer containing dye (second recording layer, second dye-containing recording layer) 25, second reflective layer 26, disk-shaped second substrate ( (Second substrate) 27 in this order. The light beam is irradiated from the first substrate 21 side, and recording / reproduction is performed. The term “transparent” means transparent to a light beam used for recording / reproducing of an optical recording medium.
[0090]
That is, this optical recording medium is a first information recording in which a first recording layer 22 containing at least a first dye and a first reflective layer 23 are sequentially laminated on a first substrate 21 having guide grooves. And a second information recording body in which at least a second reflective layer 26 and a second recording layer 25 containing a second dye are sequentially laminated on a second substrate 27 having a guide groove, The first information recording body and the second information recording body are bonded to each other through an optically transparent adhesive layer with the surface opposite to the substrate facing.
[0091]
Concavities and convexities are formed on the first substrate 21 and the second substrate 27, respectively, and constitute recording tracks. The recording track may be a convex portion or a concave portion, but the recording track 31 on the first substrate 21 is preferably constituted by a groove portion of the first substrate 21, that is, a convex portion with respect to the incident direction of light. The recording track 32 on the second substrate 27 is preferably constituted by a groove portion of the second substrate 27, that is, a concave portion with respect to the light incident direction. Unless otherwise specified, in this embodiment, the unevenness is defined with respect to the incident direction of light used for recording / reproducing. In addition, it may have uneven pits such as land prepits as necessary.
[0092]
Next, each layer will be described.
The first substrate 21, the first recording layer 22, the first reflective layer 23, the second recording layer 25, and the reflective layer 26 of the type 2 optical recording medium according to the present embodiment are respectively the first type 1 optical recording medium. The substrate 1, the first recording layer 2, the semitransparent reflective layer 3, the second recording layer 5, and the second reflective layer 6 have substantially the same configuration.
[0093]
Further, the transparent adhesive layer 24 as an intermediate layer has substantially the same configuration as the intermediate resin layer 4 provided in the type 1 optical recording medium, except that it is not necessary to form grooves and pits by unevenness. In the type 2 optical recording medium, the grooves and pits are formed on the second substrate 27 described later.
Furthermore, the buffer layer 28 as an intermediate layer has substantially the same configuration as the buffer layer provided in the type 1 optical recording medium. This buffer layer may be formed as necessary.
[0094]
The second substrate 27 preferably has shape stability so that the optical recording medium has a certain degree of rigidity. That is, it is preferable that mechanical stability is high and rigidity is large. When the first substrate 21 does not have sufficient shape stability, the second substrate 27 needs to have particularly high shape stability. In this respect, it is desirable that the hygroscopicity is small.
It is desirable that the second substrate 27 has good formability since irregularities (recording tracks) are formed. Further, although it is not necessary to be transparent, it is preferable to be transparent in the manufacturing process because the film thickness of the second recording layer 25 can be easily measured.
[0095]
Examples of such materials include those made of resins such as acrylic resins, methacrylic resins, polycarbonate resins, polyolefin resins (particularly amorphous polyolefins), polyester resins, polystyrene resins, epoxy resins, and the like. Can be used.
Concavities and convexities are provided on the second substrate 27 in a spiral shape or concentric shape to form grooves and lands. Normally, information is recorded / reproduced in / from the second recording layer 25 using such grooves and / or lands as recording tracks. Usually, since the second recording layer 25 is formed by coating, it becomes thick at the groove and is suitable for recording and reproduction. In the present optical recording medium, it is preferable that the groove portion of the second substrate 27, that is, the concave portion with respect to the light incident direction is the recording track 32. Here, a recessed part and a convex part say the recessed part and convex part with respect to the incident direction of light, respectively. Usually, the groove width is about 50 to 500 nm, and the groove depth is about 10 to 250 nm. When the recording track is spiral, the track pitch is preferably about 0.1 to 2.0 μm. In addition, it may have uneven pits such as land prepits as necessary.
[0096]
From the viewpoint of cost, the second substrate 27 having such irregularities is preferably manufactured by injection molding using a resin from a stamper having irregularities. When a resin layer made of a radiation curable resin such as a photocurable resin is provided on a substrate such as glass, irregularities such as recording tracks may be formed on the resin layer.
In recording on the optical recording medium (type 1 and type 2) obtained as described above, a laser beam focused on the recording layer with a diameter of about 0.5 to 1 μm is irradiated from the first substrate 1 and 21 side. By doing. In the portion irradiated with the laser beam, thermal deformation of the recording layer such as decomposition, heat generation, and melting due to absorption of laser beam energy occurs, and the optical characteristics change.
[0097]
The recorded information is reproduced by reading the difference in reflectance between the portion where the change in optical characteristics has occurred and the portion where the change has not occurred with the laser beam.
Further, recording and reproduction are individually performed on the two recording layers as follows. The first recording layers 2 and 22 and the second recording layers 5 and 25 can be distinguished from each other by the focus error signal obtained by the knife edge method, astigmatism method, Foucault method or the like on the focusing position of the focused laser. That is, when the objective lens for focusing the laser beam is moved up and down, S-shaped curves are respectively obtained at the positions corresponding to the first recording layers 2 and 22 and the positions corresponding to the second recording layers 5 and 25, respectively. can get. Depending on which S-curve is used for the focus servo, it is possible to select which of the first recording layers 2 and 22 and the second recording layers 5 and 25 is to be recorded and reproduced.
[0098]
In the type 1 optical recording medium, preferably, as shown in FIG. 1, the first substrate 1 and the intermediate resin layer 4 are respectively provided with irregularities, and the convex portions of the first substrate 1 and the intermediate resin layer 4 are formed. It is assumed that recording / reproduction is performed as a recording track. Usually, since the dye recording layer is formed by coating, it becomes thick at the groove and is suitable for recording and reproduction. In the type 1 optical recording medium, the groove portion of the first substrate 1, that is, the convex portion with respect to the light incident direction is used as the recording track 11, and the groove portion of the intermediate resin layer 4, that is, the convex portion is recorded with respect to the light incident direction. The track 12 is preferable.
[0099]
In the type 2 optical recording medium, preferably, as shown in FIG. 2, the first substrate 21 and the second substrate 27 are respectively provided with irregularities, and the convex portions of the first substrate 21 and the concave portions of the second substrate 27 are formed. It is assumed that recording / reproduction is performed using as a recording track. Note that the polarity of the tracking servo may be reversed between the first recording layer 22 and the second recording layer 25. In the type 2 optical recording medium, the groove portion of the first substrate 21, that is, the convex portion with respect to the light incident direction is used as the recording track 31, and the groove portion of the second substrate 27, that is, the concave portion with respect to the light incident direction is used as the recording track. 32 is preferable.
(2) Recording method of optical recording medium
Next, the recording method of the optical recording medium according to the present embodiment will be specifically described with reference to FIGS.
[0100]
FIG. 3 is a diagram showing an outline of a recording pulse strategy for explaining the present recording method. FIG. 4 is a diagram for explaining an outline of a recording pulse strategy representing the present recording method.
Here, in FIG. 3 and FIG. 4, the first pulse is a pulse for irradiating a laser that forms the start end region of the mark, and the multi-pulse is a pulse for irradiating a laser that forms the intermediate region of the mark, The last pulse is a pulse for irradiating a laser that forms the end region of the mark. T is a reference clock period used as a reference for determining the pulse strategy, T _top , T _mp , T _lp Indicates the pulse widths of the first pulse, multi-pulse, and last pulse, respectively, and dT _top Indicates the time difference between the reference clock that triggers the first pulse and the leading edge of the first pulse.
[0101]
In this recording method, according to the mark length from 3T to 14T to be recorded, a recording laser (recording laser, recording laser beam) is irradiated in combination with the first pulse, multipulse, and last pulse shown in FIG. A mark to be an information signal is formed.
For example, when a 3T mark (3T mark) is formed, a first pulse is used. When a 4T mark (4T mark) is formed, a first pulse and a last pulse are used, and a 5T mark (5T mark) is formed. In the case of forming a mark), the first pulse and multi-pulse, and the last pulse are further recorded. In the case of forming a mark of 6T or longer (such as a 6T mark), recording is performed by further increasing the multi-pulse one by one. The laser beam is irradiated to form marks with different mark lengths from 3T to 14T.
[0102]
By the way, in a single-sided incident type optical recording medium that records or reproduces information on a plurality of recording layers by irradiating laser light from one side, such as a dual-layer type single-sided incident type DVD-R, for example, When a mark that becomes an information signal is formed using a recording pulse strategy similar to that of an optical recording medium that irradiates the recording layer with laser light only through the substrate, such as single-sided DVD-R and double-sided DVD-R, jitter of the reproduction signal Will get worse.
[0103]
The reason why the jitter deteriorates in this way is not clear for a clear reason, but the following reason is presumed.
For example, when a signal is recorded on the second recording layer of a dual-layer type single-sided incidence DVD-R, the laser light transmitted through the first substrate, the first recording layer, the translucent first reflective layer, and the intermediate layer is transmitted. It is used as a recording laser beam (also called a recording laser). As described above, since the intermediate layer, the semi-transparent first reflective layer, and the like exist between the first recording layer and the second recording layer, the intensity (power) of the recording laser light reaching the second recording layer is high. When the signal is recorded on the first recording layer because the wavelength of the recording laser light changes due to the difference in refractive index between the first recording layer, the first reflective layer, and the intermediate layer. The state of the recording laser beam will change.
[0104]
In addition, when the mark is formed on the first recording layer, the mark is formed using the semi-transparent first reflection layer that is less heat-storable because it is thinner than the normal reflection layer and that has a lower reflectance than the normal reflection layer. Therefore, the heat of the irradiated laser beam is not sufficiently transmitted to the first recording layer.
Further, since the recording layer starts to form a mark after receiving a certain amount of heat and starts to form marks, a certain amount of heat is required first to start the decomposition. For this reason, even if the laser beam is actually irradiated, there is a slight delay until the mark starts to be formed. As a result, the length of the actually formed mark (mark length) tends to be shorter than the mark length to be formed. This tendency becomes more prominent as the mark length to be formed is longer and the amount of heat irradiated by the laser light is reduced.
[0105]
In addition, since the second recording layer uses a dye having higher sensitivity than the dye used for a normal single-sided recording medium or the like, the end region of the mark tends to expand mainly after the mark starts to be formed. This tendency becomes more prominent as the mark length becomes longer.
By combining these causes, for example, in a single-sided optical recording medium such as a dual-layer type single-sided DVD-R, a laser beam such as the above-mentioned single-sided DVD-R or double-sided DVD-R is used as a substrate. If a mark serving as an information signal is formed using a recording pulse strategy similar to that of an optical recording medium that irradiates the recording layer only through this, it is presumed that the jitter of the reproduction signal will deteriorate.
[0106]
Therefore, in order to reduce the jitter of the reproduction signal of each recording layer and make it favorable, for example, in a single-sided optical recording medium such as a dual-layer type single-sided incident type DVD-R, the recording laser beam incident side ( The thickness of the first recording layer and the layer interposed between the first recording layer and the second recording layer when forming a mark on the recording layer (second recording layer) located on the side far from the first substrate side) Considering the thickness and refractive index, it is conceivable to increase the power of the recording laser beam as compared with the case where the mark is formed on the recording layer (first recording layer) located on the side closer to the incident side of the recording laser beam. .
[0107]
However, it is not possible to sufficiently reduce jitter by simply increasing the power of the recording laser beam.
On the other hand, considering the control of the recording laser and the practical application of the recording apparatus, it is desirable to keep the power of the recording laser light as low as possible. Further, as the power of the recording laser beam is increased, the asymmetry value becomes worse along with this, so there is a limit to increasing the power of the recording laser beam.
[0108]
Further, if the power of the recording laser beam is lowered too much, the value of the modulation [maximum signal amplitude (maximum mark amplitude; Modulation; I14 / I14H)] will deteriorate.
In particular, a recording method from a new point of view is required in order to suppress the spread of the mark termination region, which has not been a problem with conventional single-sided recording media and the like.
Therefore, in the present embodiment, when a mark is formed on the recording layer (second recording layer) located on the side far from the recording laser beam incident side (first substrate side) (that is, through another recording layer). When a mark is formed by irradiating a pulsed recording laser beam), the asymmetry value is within a desired range (for example, around 0) [here, the modulation value is also a desired value or more (for example, 0.6 or more)]. Then, after adjusting the power of the recording laser beam so as to be, the recording method is devised as described below so as to reduce the jitter.
[0109]
In particular, if the lowest one of the recording laser light powers in which the asymmetry value is within a desired range (eg, near 0) and the jitter is a predetermined value (eg, 9%) or less, the power of the recording laser light is reduced. It can be kept low. Note that the modulation value is preferably set to a desired value or more (for example, 0.6 or more).
In this embodiment, in an optical recording medium in which a recording laser is irradiated from one side to form a mark serving as an information signal for a plurality of recording layers, a first pulse for forming a mark start end region and a mark end The last pulse for forming the region is irradiated, and the mark is formed by changing the position of the front edge of the first pulse and / or the position of the rear edge of the last pulse according to the length of the mark. Yes.
[0110]
This is because the shape of the start and end regions of the formed mark is determined by the position of the leading edge of the first pulse and the position of the trailing edge of the last pulse, and has a large effect on jitter.
In particular, when a mark is formed based on a recording pulse strategy as shown in FIG. 4A, as shown in FIGS. 3 and 4B, the first of FIG. Without moving the trailing edge of the pulse (with the trailing edge fixed), only the leading edge is moved (the leading edge is dT _top The first pulse width T) _top Is preferably widened (the irradiation time of the recording laser light is increased). DT _top , Increase the value of the first pulse to advance the start timing of the first pulse, the pulse width T of the first pulse _top To increase the total irradiation amount of the recording laser light irradiated to form one mark and increase the initial heat amount necessary to start the formation of the mark. It is preferable to do this.
[0111]
As described above, the pulse width of the first pulse is widened to increase the amount of irradiation of the recording laser beam because the amount of heat given to the recording layer by the irradiation of the recording laser beam is conducted in the recording layer. When a recording laser beam is irradiated for a certain period of time to form a mark having a desired length, it is possible to effectively use the heat applied to the recording layer by first providing a sufficient amount of heat, This is because the spread of the mark can be suppressed.
[0112]
Here, by changing the position of the front edge of the first pulse in accordance with the length of the mark, the pulse width of the first pulse is increased as the mark length increases. In particular, it is preferable that the pulse width of the first pulse is increased stepwise by appropriately dividing the 4T mark to the 14T mark into groups.
In particular, the recording method of widening the pulse width of such a first pulse can provide an effect of reducing jitter even when applied to an optical recording medium having any of the type 1 and type 2 structures described above.
[0113]
It is not preferable to move the trailing edge of the first pulse. When the rear edge is moved, the start of laser irradiation is delayed, so the start of mark formation is delayed. This is because it adversely affects the jitter.
Further, as shown in FIG. 4C, the trailing edge of the last pulse in FIG. 3 is moved in accordance with the length of the mark to be formed (dT _lp Last pulse width T) _lp It is also preferable to narrow the width (reducing the irradiation time of the recording laser light). DT _lp Is the time difference between the trailing edge of the basic last pulse (for example, the last pulse of the recording pulse strategy used for recording on the first recording layer) and the trailing edge when the pulse width of the last pulse is narrowed.
[0114]
Here, by changing the position of the trailing edge of the last pulse in accordance with the length of the mark, the pulse width of the last pulse is narrowed as the length of the mark increases. In particular, it is preferable that the pulse width of the last pulse is narrowed stepwise by appropriately dividing the 4T mark to the 14T mark into groups.
When a mark is formed by irradiating a recording laser beam for a certain period of time or longer, the recording layer already has a sufficient amount of heat in the end region of the mark, and the mark can be formed using the heat. In this case, if too much heat is applied to the mark termination region, an unnecessarily large mark is formed. Therefore, shortening the trailing edge of the last pulse forming the trailing edge region of the mark can suppress the spread of the mark and improve the jitter.
[0115]
Here, the longer the length of the mark, the longer the irradiation time of the recording laser beam, the more easily the heat is applied, and the easier the spread of the mark. The longer the mark length, the narrower the pulse width of the last pulse. Thus, the amount of heat necessary for forming the mark is given according to the length of the mark.
In particular, even if such a recording method for narrowing the pulse width of the last pulse is applied to the optical recording medium of any of the type 1 and type 2 structures described above, the effect of reducing jitter can be obtained. When applied to a type 2 optical recording medium, the effect is great.
[0116]
That is, in the type 2 optical recording medium according to this embodiment, recording is performed on the land portion of the second recording layer 25, but the film thickness of the land portion of the second recording layer 25 is thin. In general, when the recording layer is thin, the amount of heat required for forming the mark is reduced, and the sensitivity of the recording layer is increased. Therefore, in the type 2 optical recording medium with good recording sensitivity, correcting the trailing edge position of the last pulse (moving it forward) and narrowing the pulse width (shortening the irradiation time) The spread can be suppressed, and the effect is particularly great.
[0117]
The amount of change in the position of the front edge of the first pulse and the position of the rear edge of the last pulse can be determined experimentally as appropriate depending on the configuration of the optical recording medium and the power and wavelength of the irradiated laser beam. In general, the movement width of the front edge position of the first pulse is 5% or more and 50% or less of the pulse width of the first pulse, and the movement width of the rear edge position of the last pulse is generally the last pulse. The pulse width is 5% or more and 50% or less.
[0118]
Furthermore, as shown in FIG. 4D, it is also preferable that the maximum power of the pulse component of the recording laser beam corresponding to the first pulse is larger than the pulse component of the recording laser beam corresponding to the last pulse.
As described above, a certain amount of heat is required first to form the mark start end region. However, when the irradiation power of the entire recording laser to be irradiated is increased, an unnecessary amount of heat is also given, and the mark spreads. Therefore, the maximum power of the pulse component of the recording laser beam corresponding to the first pulse is increased to momentarily give a large amount of heat, that is, only the initial amount of heat necessary for starting the formation of the mark start end region is increased to form the mark. It is preferable to do this.
[0119]
In this way, when the power of the recording laser beam corresponding to the first pulse is made larger than the power of the recording laser beam corresponding to the multi-pulse or the last pulse (this is called “Powered”), the first pulse and the multi-pulse In addition, since the power of the recording laser beam corresponding to the multi-pulse and the last pulse can be lowered as compared with the case where the power of the recording laser beam corresponding to the last pulse is the same, the power of the recording laser beam as a whole is reduced. Can be lowered. This is because when the power of the recording laser light irradiated corresponding to the first pulse is increased, a large amount of heat is instantaneously applied, and the given amount of heat conducts through the recording layer, so it supports multi-pulses and last pulses. It is considered possible to reduce the power of the recording laser light.
[0120]
Here, the difference in power between the pulse component of the recording laser corresponding to the first pulse and the pulse component of the recording laser corresponding to the last pulse (or multi-pulse) is the pulse component of the recording laser corresponding to the first pulse. The power is preferably 5% or more, preferably 10% or more larger than the power of the pulse component of the recording laser corresponding to the last pulse (or multi-pulse). This is because if it is equal to or greater than this value, the mark start end region can be formed effectively without delaying the mark formation.
[0121]
Further, the difference is 30% or less, preferably 20% or less. If the difference is too much, the shape of the start end region and the rear end region of the mark becomes unbalanced as the mark length becomes longer, and the reproduction characteristics deteriorate, such as a decrease in modulation.
In particular, the recording method for increasing the power of the recording laser light irradiated corresponding to the first pulse as described above reduces the jitter even when applied to the optical recording medium of any of the above type 1 and type 2 structures. However, the effect is particularly great when applied to a type 2 optical recording medium.
[0122]
That is, in the type 2 optical recording medium according to this embodiment, recording is performed on the land portion of the second recording layer 25, but the film thickness of the land portion of the second recording layer 25 is thin. In general, when the recording layer is thin, the amount of heat required for forming the mark is reduced, and the sensitivity of the recording layer is increased. Therefore, in the type 2 optical recording medium with good recording sensitivity, increasing the power of the recording laser light irradiated corresponding to the first pulse causes unnecessary mark spread and signal leakage to the adjacent track. This is particularly effective.
[0123]
In the recording method of the optical recording medium for forming a mark that becomes an information signal for a plurality of recording layers by irradiating a recording laser from one side of the present invention, it is not always necessary to use all of the above recording methods. What is necessary is just to record combining these recording methods suitably so that a desired reproduction | regeneration characteristic may be acquired.
In general, when marks are formed on the first recording layer of a dual layer medium, sufficient reproduction characteristics can often be obtained by correcting the leading edge of the first pulse and the trailing edge of the last pulse.
[0124]
In particular, when a mark is formed on the second recording layer of a type 1 dual layer medium, sufficient reproduction characteristics can often be obtained simply by correcting the front edge of the first pulse. On the other hand, when forming a mark on the second recording layer of the type 2 dual layer medium, a recording method for correcting the leading edge of the first pulse, a recording method for correcting the trailing edge of the last pulse, If recording is performed in combination with a recording method in which the maximum power of the pulse component of the recording laser corresponding to the first pulse is larger than the pulse component of the recording laser corresponding to (pulse), sufficient reproduction characteristics can be easily obtained.
[0125]
In the present invention, when a mark of 5T or more is formed, a multi-pulse laser (a recording laser corresponding to a multi-pulse) is irradiated. However, the pulse width of the multi-pulse laser may be appropriately changed.
Therefore, according to the recording method of the optical recording medium according to the present embodiment, the mark start end region is applied to the optical recording medium that records or reproduces information on a plurality of recording layers by irradiating laser light from one side. Since the start of formation and the end of formation of the termination region can be controlled in accordance with a desired mark length, there is an advantage that a signal having good reproduction characteristics with low jitter can be formed. Further, according to the present invention, there is an advantage that a signal can be stably formed even if the recording power fluctuates.
[0126]
Further, according to the recording method of the optical recording medium according to the present embodiment, when the mark is formed by irradiating the second recording layer with the pulsed recording laser light, the value of the asymmetry falls within a desired range. In this case, the power of the recording laser beam is adjusted and the start end region of the mark is formed in accordance with the length of the mark, so that the modulation value is equal to or greater than a desired value (for example, 0.6 or more). In order to change the pulse width of the first pulse or the pulse width of the last pulse for forming the end region of the mark, the asymmetry value is set within a desired range (for example, near 0). Jitter can be reduced to a predetermined value (for example, 9%) or less, while being equal to or greater than (for example, 0.6 or more).
[0127]
In this case, the asymmetry value is within a desired range (eg, near 0) [here, the modulation value is also greater than the desired value (eg, 0.6 or more)], and the jitter is less than a predetermined value (eg, 9% or less). If the lowest recording laser light power is selected, the recording laser light power can be kept low.
In the above-described embodiment, the recording method in the case where the mark is formed on the recording layer (second recording layer) located on the side far from the recording laser beam incident side (first substrate side) has been described. In order to form a mark on the recording layer (first recording layer) located on the side closer to the incident side (first substrate side) of the laser light for use, a laser such as a single-sided DVD-R or a double-sided DVD-R is used. A recording pulse strategy similar to that of an optical recording medium that irradiates the recording layer with light only through the substrate may be used.
[0128]
However, in the case of a single-side incident type optical recording medium having a plurality of recording layers and capable of recording or reproducing information on each recording layer by irradiating laser light from one side, for example, to the first recording layer Since a semi-transparent reflective layer is used for recording in this case, in consideration of the effect of the semi-transparent reflective layer, when forming a mark on the first recording layer [that is, without passing through another recording layer (recording laser beam) [When forming a mark by irradiating a recording layer located on the side closest to the incident side of the laser beam by irradiating a pulsed laser beam for recording] to form the start end region of the mark according to the length of the mark It is preferable to change the position of the leading edge of the first pulse (pulse width of the first pulse) and / or the position of the trailing edge of the last pulse for forming the end region of the mark (pulse width of the last pulse).
[0129]
Specifically, it is preferable to increase the pulse width of the first pulse for forming the mark start end region as the mark length increases. In particular, it is preferable that the pulse width of the first pulse is increased stepwise by appropriately dividing the 4T mark to the 14T mark into groups.
Further, it is preferable that the pulse width of the last pulse for forming the end region of the mark is narrowed as the length of the mark is increased. In particular, it is preferable that the pulse width of the last pulse is narrowed stepwise by appropriately dividing the 4T mark to the 14T mark into groups.
[0130]
As described above, when a mark is formed by irradiating the first recording layer with a pulsed recording laser beam (without passing through another recording layer), the leading edge of the first pulse is changed according to the length of the mark. Jitter can be reduced by changing the position and / or the position of the trailing edge of the last pulse.
In this case, the power of the recording laser beam is adjusted so that the asymmetry value is within a desired range (for example, around 0) [here, the modulation value is also larger than the desired value (for example, 0.6 or more)]. It is preferable to do this.
[0131]
In this way, the power of the recording laser beam is adjusted so that the asymmetry value is within a desired range [here, the modulation value is also greater than or equal to a desired value (for example, 0.6 or greater)], and the mark By changing the pulse width of the first pulse for forming the mark start edge region in accordance with the length of the mark, the asymmetry value falls within a desired range (for example, near 0) [here, the modulation value is also Jitter can be reduced to a predetermined value (for example, 9%) or less while maintaining a desired value or more (for example, 0.6 or more).
[0132]
In this case, the power of the recording laser beam can be kept low by selecting the lowest recording laser beam power at which the jitter is equal to or less than a predetermined value.
Here, the write-once optical recording medium including the dye-containing recording layer (here, DVD-R, DVD + R) has been described. However, the optical recording medium is not limited to this, and laser light irradiation from one side is performed. As long as the optical recording medium includes a plurality of recording layers capable of recording or reproducing information. For example, as a recording layer, for example, a rewritable optical recording medium (for example, a DVD-RW, DVD + RW, DVD-RW, etc.) including a phase change recording layer in which a crystalline portion is in an unrecorded / erased state and an amorphous portion is in a recorded state. DVD-RAM, etc.) or a magneto-optical type optical recording medium including a magnetic recording layer as a recording layer.
[0133]
Further, here, the case where the present invention is applied to an optical recording medium having two recording layers capable of recording or reproducing information by irradiation with a laser beam from one side is described, but the present invention is not limited to this. For example, the present invention can also be applied to an optical recording medium that includes three or more recording layers and can record or reproduce information by irradiation with laser light from one side.
[0134]
In this embodiment, the recording method of the optical recording medium has been described. However, a recording pulse strategy (write strategy) set based on this recording method is mounted on, for example, a recording apparatus of the optical recording medium.
In other words, an optical recording medium recording apparatus (drive, writer) includes a spindle motor that rotates the optical recording medium, a semiconductor laser (laser light source) such as a laser diode (LD), a beam splitter, an objective lens, such as a photodiode. (PD) or other optical pickup including a photodetector, a laser driver (driving unit; for example, a driving circuit) for driving a semiconductor laser, and a pulse (signal) output to the laser driver based on data to be recorded A recording pulse strategy circuit (recording pulse strategy control unit) that performs control [power modulation control of recording laser beam (multi-pulse modulation control)], and a control calculation unit that performs control for each device [for example, CPU or memory (storage unit) ) Is included]. The recording pulse strategy circuit and the control calculation unit are collectively referred to as a recording laser control unit.
[0135]
When a recording command (write command) is input to the control arithmetic unit, the control arithmetic unit outputs a control signal, and the laser driver drives the semiconductor laser based on the signal subjected to power modulation control by the recording pulse strategy circuit To do. As a result, data recording is performed by irradiating a desired recording layer of the optical recording medium with laser light (recording light) from a semiconductor laser via a beam splitter, an objective lens, or the like.
[0136]
Therefore, a recording pulse strategy (recording pulse modulation pattern) determined based on the above-described recording method may be set in the recording pulse strategy circuit constituting the recording laser control unit. Thereby, power modulation control is performed based on the recording pulse strategy set in the recording pulse strategy circuit, and based on this, recording laser light is emitted from the semiconductor laser, and a desired mark is formed to record information. Will be.
[0137]
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
[0138]
【Example】
Examples are shown below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. All percentages in the examples are based on weight unless otherwise specified.
(Production of optical recording medium)
In this example, two types of optical recording media of type 1 and type 2 were produced.
[0139]
First, a type 1 optical recording medium was prepared as follows.
A first substrate having a diameter of 120 mm and a thickness of 0.6 mm having a land and pre-pits having a groove pitch of 0.74 μm, a groove width of 0.3 μm, and a groove depth of 130 to 170 nm, by injection molding polycarbonate using a Ni stamper Was made. Next, a 0.2% octafluoropentanol solution of a metal-containing azo dye was applied onto the first substrate by spin coating, and heat-treated at 100 ° C. for 30 minutes to form a first recording layer (maximum Absorption wavelength (λmax) of about 600 nm). Next, an Ag alloy containing 97 atomic% or more of Ag was sputtered to a thickness of 15 to 20 nm to form a first reflective layer having a transmittance of 40% or more. Thus, the first information recording substrate was produced.
[0140]
Next, an ultraviolet curable resin is applied on the first reflective layer to a thickness of 25 to 40 μm, and a resin stamper prepared in advance is placed with the concavo-convex surface facing the first substrate. Then, after the ultraviolet curable resin is cured by irradiating ultraviolet rays from the resin stamper side, the resin stamper is peeled off, and the groove pitch is 0.74 μm, the groove width is 0.3 μm, and the groove depth is 130 as in the first substrate. Lands and prepits of ˜170 nm were formed.
[0141]
Next, a 0.2% octafluoropentanol solution of the same metal-containing azo dye as used for the first recording layer is applied on the intermediate layer by a spin coating method, and heat-treated at 100 ° C. for 30 minutes. After forming the second recording layer, an Ag alloy containing 97 atomic% or more of Ag is sputtered to a thickness of 100 to 150 nm to form a second reflective layer, which is made of an ultraviolet curable resin. A protective layer having a thickness of 5 to 10 μm is provided, and an adhesive made of an ultraviolet curable resin (Nippon Kayaku DVD576M) is applied on the protective layer to a thickness of 40 to 70 μm, and the diameter is prepared in advance. A second substrate made of polycarbonate having a thickness of 120 mm and a thickness of 0.6 mm was placed, and subsequently, an ultraviolet ray was irradiated from the second substrate side to cure the adhesive layer, thereby producing a type 1 optical recording medium. .
[0142]
On the other hand, the type 2 optical recording medium was produced as follows.
Using a Ni stamper, polycarbonate is injection-molded to produce a first substrate with a diameter of 120 mm and a thickness of 0.6 mm having lands and prepits with a groove pitch of 0.74 μm, a groove width of 350 nm, and a groove depth of 30 to 70 nm. did. Next, an Ag alloy containing 97 atomic% or more of Ag was sputtered to a thickness of 100 nm to form a second reflective layer. Next, a 0.2% octafluoropentanol solution of a metal-containing azo dye was applied onto the second reflective layer by a spin coating method, and heat-treated at 100 ° C. for 30 minutes to form a second recording layer (maximum Absorption wavelength (λmax) of about 600 nm). Next, on this second dye-containing recording layer, a silver alloy containing 97% or more of Ag is sputtered to form a buffer layer, and an ultraviolet resin (SPC-920 manufactured by Nippon Kayaku Co., Ltd.) is formed on the buffer layer. A protective layer was formed by spin coating to a thickness of 5 to 7 um.
[0143]
The first information substrate described in the production of the separately manufactured type 1 optical recording medium is applied by spin coating a radical ultraviolet curing resin (adhesive) (Nippon Kayaku DVD576M) on the protective layer. To make a type 2 optical recording medium.
(Signal recording and evaluation method)
Using an evaluation machine (DDU-1000 manufactured by Pulstec Corp., maximum recording power 15 mW) equipped with a semiconductor laser having a wavelength of 657 nm (NA = 0.65), a recording linear velocity density of 3.8 m / s, a reference clock period of 38.5 ns (1/26 Mbps), EFM + signal of 8-16 modulation was recorded with marks having a mark length of 3T to 14T at a recording power at which the asymmetry of the recording signal is near 0 (here, the modulation is 0.6 or more). Thereafter, the recorded signal was reproduced at a reproduction linear velocity density of 3.8 m / s and a reproduction power of 0.7 mW, and the average value of jitter (signal deviation) of the reproduction signal of the mark having a mark length of 3T to 14T was measured.
(Example 1)
In the first recording layer of the type 1 optical recording medium produced as described above, according to the recording pulse strategy shown in Table 1, a first pulse and a last pulse are changed according to the length of the mark, and a signal is recorded. Thereafter, the signal was reproduced and the jitter of the reproduced signal was measured. FIG. 5 shows measurement results obtained by measuring jitter (vertical axis) and recording laser power (horizontal axis).
[0144]
[Table 1]

[0145]
(Example 2)
According to the recording pulse strategy shown in Table 2, a signal was recorded in the same manner as in Example 1 except that the first pulse was changed according to the length of the mark, and then the signal was reproduced and the jitter of the reproduced signal was measured. FIG. 5 shows measurement results obtained by measuring jitter (vertical axis) and recording laser power (horizontal axis).
[0146]
[Table 2]

[0147]
(Example 3)
According to the recording pulse strategy shown in Table 3, a signal was recorded in the same manner as in Example 1 except that the last pulse was changed according to the length of the mark, and then the signal was reproduced and the jitter of the reproduced signal was measured. FIG. 5 shows measurement results obtained by measuring jitter (vertical axis) and recording laser power (horizontal axis).
[0148]
[Table 3]

[0149]
Example 4
A signal is recorded on the second recording layer of the type 1 optical recording medium in accordance with the recording pulse strategy shown in Table 4 by changing the first pulse according to the length of the mark, and then the signal is reproduced and the jitter of the reproduced signal is recorded. Was measured. FIG. 6 shows measurement results obtained by measuring jitter (vertical axis) and recording laser power (horizontal axis).
[0150]
[Table 4]

[0151]
(Example 5)
A signal was recorded on the second recording layer of the type 2 optical recording medium in the same manner as in Example 1 except that the first pulse and the last pulse were changed according to the length of the mark according to the recording pulse strategy shown in Table 5. Thereafter, the signal was reproduced and the jitter of the reproduced signal was measured. Measurement results obtained by measuring the jitter (vertical axis) and the power of the recording laser (horizontal axis) are shown in FIGS.
[0152]
[Table 5]

[0153]
(Example 6)
According to the recording pulse strategy shown in Table 6, a signal was recorded in the same manner as in Example 5 except that the first pulse was changed according to the length of the mark, and then the signal was reproduced and the jitter of the reproduced signal was measured. FIG. 7 shows measurement results obtained by measuring jitter (vertical axis) and recording laser power (horizontal axis).
[0154]
[Table 6]

[0155]
(Example 7)
According to the recording pulse strategy shown in Table 7, a signal was recorded in the same manner as in Example 5 except that the last pulse was changed according to the length of the mark, and then the signal was reproduced and the jitter of the reproduced signal was measured. FIG. 7 shows measurement results obtained by measuring jitter (vertical axis) and recording laser power (horizontal axis).
[0156]
[Table 7]

[0157]
(Example 8)
According to the recording pulse strategy shown in Table 8, a signal was recorded in the same manner as in Example 5 except that the power of the pulse component of the recording laser corresponding to the first pulse was increased by 10%. Was measured. FIG. 8 shows measurement results obtained by measuring jitter (vertical axis) and recording laser power (horizontal axis). The power of the recording laser on the horizontal axis in FIG. 8 indicates the power value of the last pulse.
[0158]
[Table 8]

[0159]
Example 9
According to the recording pulse strategy shown in Table 9, the signal was recorded in the same manner as in Example 5 except that the power of the pulse component of the recording laser corresponding to the first pulse was increased by 20%, and then the signal was reproduced and the jitter of the reproduced signal Was measured. FIG. 8 shows measurement results obtained by measuring jitter (vertical axis) and recording laser power (horizontal axis). The power of the recording laser on the horizontal axis in FIG. 8 indicates the power value of the last pulse.
[0160]
[Table 9]

[0161]
(Comparative Example 1)
According to the recording pulse strategy of the prior art shown in Table 10, the signal is recorded in the same manner as in Example 1 without changing the first pulse and the last pulse according to the length of the mark, and then the signal is reproduced and the jitter of the reproduced signal is reproduced. Was measured. The measurement results are shown in FIG.
[0162]
[Table 10]

[0163]
(Comparative Example 2)
According to the recording pulse strategy of the prior art shown in Table 11, without changing the first pulse and the last pulse according to the mark length, the signal is recorded in the same manner as in Example 4, and then the signal is reproduced and the jitter of the reproduced signal is reproduced. Was measured. The measurement results are shown in FIG.
[0164]
[Table 11]

[0165]
(Comparative Example 3)
According to the recording pulse strategy of the prior art shown in Table 12, the signal is recorded in the same manner as in Example 5 without changing the first pulse and the last pulse in accordance with the length of the mark, and then the signal is reproduced and the jitter of the reproduced signal is reproduced. Was measured. The measurement results are shown in FIG.
[0166]
[Table 12]

[0167]
(Summary)
FIG. 5 is a diagram showing the relationship between the power of the recording laser and the jitter of the reproduction signal when a signal is recorded on the first recording layer of the type 1 optical recording medium.
As is apparent from FIG. 5, the jitter in the first example in which the first pulse and the last pulse are changed is improved as compared with the comparative example 1 in which nothing is changed. Further, in Example 1, even when the recording power changes, the jitter value does not vary so much and is stable at a low value. Therefore, the margin for the power fluctuation of the recording laser is large and signal recording can be performed stably.
[0168]
In Example 2 in which only the first pulse is changed and in Example 3 in which only the last pulse is changed, jitter is improved as compared with Comparative Example 1, and a margin for power fluctuation of the recording laser is increased. The effect of the present invention is proved.
FIG. 6 is a diagram showing the relationship between the power of the recording laser and the jitter of the reproduction signal when a signal is recorded on the second recording layer of the type 1 optical recording medium.
[0169]
As is apparent from FIG. 6, the jitter is improved in Example 4 in which the first pulse is changed, compared to Comparative Example 2 in which nothing is changed. Further, in Example 4, even when the recording power is changed, the jitter value does not vary so much and is stable at a low value. Therefore, the margin for the power fluctuation of the recording laser is large and signal recording can be performed stably.
[0170]
FIG. 7 is a diagram showing the relationship between the power of the recording laser and the jitter of the reproduction signal when a signal is recorded on the second recording layer of the type 2 optical recording medium.
As can be seen from FIG. 7, in Example 5 in which the first pulse and the last pulse are changed, the jitter is improved as compared with Comparative Example 3 in which nothing is changed. Further, in Example 5, compared to Comparative Example 3, jitter fluctuations near the optimum recording power that can suppress jitter are small, a margin for power fluctuations of the recording laser is large, and signal recording can be performed stably. Can be done.
[0171]
Further, in Example 6 in which only the first pulse is changed and Example 7 in which only the last pulse is changed, jitter is improved as compared with Comparative Example 3, and a margin for power fluctuation of the recording laser is increased. .
FIG. 8 shows the recording laser power and the reproduction signal when the power of the pulse component of the recording laser corresponding to the first pulse is changed when the signal is recorded on the second recording layer of the type 2 optical recording medium. It is a figure which shows the relationship of a jitter.
[0172]
As is apparent from FIG. 8, in Example 8 in which the power of the pulse component of the recording laser corresponding to the first pulse is increased by 10% and Example 9 in which the power is increased by 20%, the power is changed. The jitter is improved as compared with the fifth embodiment.
[0173]
【The invention's effect】
According to the recording method and the recording apparatus of the optical recording medium of the present invention, the mark start end region is formed on the optical recording medium which records or reproduces information on a plurality of recording layers by irradiating laser light from one side Since the start and end of formation of the end region can be controlled in accordance with a desired mark length, there is an advantage that a signal having good reproduction characteristics with low jitter can be formed. Further, according to the present invention, there is an advantage that a signal can be stably formed even if the recording power fluctuates.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an optical recording medium (type 1) according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing an optical recording medium (type 2) according to an embodiment of the present invention.
FIG. 3 is a schematic diagram showing an outline of a recording pulse strategy for explaining a recording method of an optical recording medium according to an embodiment of the present invention.
FIG. 4 is a schematic diagram showing an outline of a recording pulse strategy representing a recording method of an optical recording medium according to an embodiment of the present invention.
FIG. 5 is a diagram showing the relationship between the power of a recording laser and the jitter of a reproduction signal when a signal is recorded on the first recording layer of the optical recording medium (type 1) according to the embodiment of the present invention.
FIG. 6 is a diagram showing the relationship between the power of a recording laser and the jitter of a reproduction signal when a signal is recorded on the second recording layer of the optical recording medium (type 1) according to the embodiment of the present invention.
FIG. 7 is a diagram showing a relationship between recording laser power and reproduction signal jitter when a signal is recorded on the second recording layer of the optical recording medium (type 2) according to the embodiment of the present invention.
FIG. 8 shows the change of the power of the pulse component of the recording laser corresponding to the first pulse when a signal is recorded on the second recording layer of the optical recording medium (type 2) of the optical recording medium according to the embodiment of the present invention. FIG. 6 is a diagram showing a relationship between recording power and reproduction signal jitter in the case of recording.
[Explanation of symbols]
1,21 First substrate (first substrate)
2,22 First recording layer (first recording layer)
3,23 first reflective layer
4 Intermediate resin layer (intermediate layer)
5, 25 Second recording layer (second recording layer)
6,26 Second reflective layer
7 Adhesive layer
8, 27 Second substrate (second substrate)
28 Buffer layer
Recording track consisting of 11, 12, 31 convex parts
24 Transparent adhesive layer (intermediate layer)
32 Recording track consisting of recesses

Claims (11)

An optical recording medium for forming a mark having a length nT (n is a natural number of 4 or more and 14 or less, T is a reference clock cycle) that is irradiated with a recording laser from one side and becomes an information signal for a plurality of recording layers In the recording method,
At least a first pulse for forming the mark start region and a last pulse for forming the mark end region are used to irradiate the recording laser in a pulse shape to form a mark of length nT. In this case, a mark is formed by changing the position of the leading edge of the first pulse and / or the position of the trailing edge of the last pulse according to the length of the mark. . 2. The optical recording medium recording method according to claim 1, wherein the pulse width is increased by correcting the position of the front edge of the first pulse as the mark length increases. 3. The optical recording medium recording method according to claim 1, wherein the pulse width is shortened by correcting the position of the trailing edge of the last pulse as the mark length increases. The maximum power of the pulse component of the recording laser corresponding to the first pulse is made larger than the pulse component of the recording laser corresponding to the last pulse. The recording method of the optical recording medium as described in 2. 5. The optical recording medium recording method according to claim 1, wherein the mark is formed on a recording layer other than the recording layer closest to the incident position of the recording laser. 5. The optical recording medium recording method according to claim 1, wherein the mark is formed on a recording layer closest to an incident position of the recording laser. 6. 7. When forming a mark having a length of 5T or more among the marks, the recording laser is irradiated with a multi-pulse for forming an intermediate region of the mark. The recording method of an optical recording medium according to any one of the above. The recording method for an optical recording medium according to any one of claims 1 to 7, wherein the recording layer is a dye-containing recording layer. A recording apparatus for an optical recording medium that records information by forming a mark of a desired length on each recording layer by making a recording laser beam incident from one side of an optical recording medium having a plurality of recording layers,
When the mark is formed by irradiating a pulsed recording laser beam through another recording layer, the pulse width of the first pulse for forming the start end region of the mark according to the length of the mark and / or Alternatively, the optical recording medium recording apparatus is configured to change a pulse width of a last pulse for forming the end region of the mark. A recording apparatus for an optical recording medium that records information by forming a mark of a desired length on each recording layer by making a recording laser beam incident from one side of an optical recording medium having a plurality of recording layers,
When the mark is formed by irradiating a pulsed recording laser beam without passing through another recording layer, the pulse width of the first pulse for forming the start end region of the mark according to the length of the mark and An apparatus for recording an optical recording medium, wherein the recording apparatus is configured to change a pulse width of a last pulse for forming an end region of the mark. When the mark is formed by irradiating pulsed recording laser light, the power of the recording laser light is adjusted so that an asymmetry value falls within a desired range. Item 15. A recording apparatus for an optical recording medium according to Item 9 or 10.

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