JP3731244B2 - Optical recording medium and manufacturing method thereof - Google Patents

Description

【０００８】
（式中、Ｘはジアゾ基と共役可能な電子吸引基からなる置換基を示し、Ｙはヒドロキシル基、カルボキシル基よりなる置換基を示し、Ｒ^１、Ｒ^２は炭素数１〜６のアルキル基を示し、Ｍ^２＋はニッケル、コバルト又は銅の２価のイオンを示す。）
【０００９】
【発明の実施の形態】
以下、本発明の実施の形態について説明する。
本発明における記録層は、記録用のレーザー光を吸収することによる昇温で減量し、膜厚が減少し、光学特性が変化することにより、戻り光の位相が変化し、反射率が変化したところを記録部とするものである。
【００１０】
本発明において、透明基板としてはポリカーボネート、ポリメタクリレート、非晶質ポリオレフィン等の樹脂やガラス等の公知のものが用いられ、サーボ用の案内溝を有している。その溝は、深さは、通常１００〜２００ｎｍ、好ましくは、１４０〜２００ｎｍで、溝幅は、通常０.３〜０.４μｍ、トラックピッチは、通常０.７〜１.０μｍであり、溝形状はＵ字型溝が好ましい。溝の深さは、１００ｎｍ未満の場合には記録時に十分な変化がおきず、十分な記録変調度が得られない場合がある。２００ｎｍを越えると、溝部と溝間部の反射率差が大きすぎるため、溝上記録の場合には反射率が低くなりすぎるので好ましくはない。溝幅は、０．３μｍ未満には十分なトラッキングエラー信号強度を得ることが困難となる恐れがある。また、０．４μｍを越える溝幅の場合には、記録した時に記録部が横に広がりやすくなるので好ましくない。トラックピッチは、高容量化の用途には、０．７〜１．０μｍが好ましい。なお、溝形状は、１μｍピッチの場合はＨｅーＣｄレーザーによる光学測定で求め、それよりもトラックピッチが狭い場合には、ＳＴＭやＡＦＭでプロファイルを測定して求めることができる。なお、後述の実施例においては、ＳＴＭで求めた。
【００１１】
記録層は、例えば、有機色素等をエタノール、３ーヒドロキシー３ーメチルー２ーブタノン、ジアセトンアルコール、フッ化アルコール等の溶媒に溶かした溶液をスピンコートして得られる。特に、この溶媒としては、沸点が１１０〜１５０℃のフッ化アルコールが好ましく用いられる。沸点が１００℃未満の場合は、スピンコート時に溶媒が気化するため、ディスクの半径４０ｍｍより外周側に塗布液がゆきつかず、半径方向の膜厚分布が極めて大きくなり、良好な特性が得られないことがあるので好ましくない。また、１７０℃を越える場合には、蒸発に時間がかかる上に、膜中に溶媒が残留しやすく、その様な場合には、良好な記録感度が得られないことが多い。フッ化アルコール以外のよく使用される溶媒、たとえば、ジアセトンアルコールやエチルセロソルブ等は、基板のポリカーボネートとの接触角が３０度以上であるのに対し、上記フッ化アルコールは１０度以下であり、フッ化アルコールのこの様な濡れ性の良さの故に、狭トラックピッチレプリカの溝内に十分塗布液が入り込めるため、良好な記録特性を示す膜を形成することが可能となる。また、ケトン系あるいは、その他の極性溶媒は、基板のポリカーボネートを溶かすため、基板上に誘電体膜をスパッタしたり、高価なポリオレフィンやガラスにする必要が生じ、有機系記録媒体の安価性、プロセスの容易性というメリットが失われてしまうため好ましくない。
【００１２】
膜厚は溝部で６０〜１８０ｎｍ程度が好ましい。６０ｎｍ未満では薄すぎて良好な記録特性が得られにくい恐れがある。また、１８０ｎｍを越えると、記録部の横方向、スキャン方向への変形が大きくなるため、クロストークやジッターが大きくなるため好ましくない。また、塗布膜の溝深さが５０〜１８０ｎｍであり、Ｕ字型であることが好ましい。この溝深さが５０ｎｍ未満であると、トラッキングエラー信号振幅が十分に得られなくなり、また、１８０ｎｍを越える場合には溝部の膜厚が薄すぎるため、十分な記録変調度が得られない恐れがある。
【００１３】
有機色素としては、シアニン色素、含金属アゾ系色素や、ジベンゾフラノン系、含金属インドアニリン等があるが、本発明では、前記一般式［１］で表される含金属アゾ系色素が特に好ましい。前記式中のＸとしてはＢｒ、Ｃｌ、ＣＦ₃等が例示できる。また、Ｒ¹、Ｒ²は炭素数１〜６の直鎖アルキル基でも炭素数３〜６の分岐アルキル基でもよい。たと
えば、次のような色素が例示できる。
【００１４】
【化５】

【００１５】
【化６】

【００１６】
特にこの系統の色素に関しては、広くは特公平５ー６７４３８号公報等に記載されているが、その中で、高密度記録用途に限定する場合には、熱特性、膜としてのモル吸光係数等の要請から、上記の例示のような特定の色素に限定されることがわかり、本発明に到達した。
前記化合物は、ジアゾ基と共役可能な位置に電子吸引性基の置換をすることにより、ジアゾ結合が不安定化すると考えられ、その結果、分解時の減量が急峻になるため、高密度記録用に優れた特性を示すものと考えられる。
【００１７】
記録層を構成する有機色素の熱的特性は記録特性に大きく影響する。短波長用途として充分な特性を得るためには、熱重量分析における、主減量過程での減量が、温度に対してシャープであることが必要であり、１０℃／分の昇温速度で測定した場合の主減量過程での減量の傾きが１０％/℃となる有機色素を用いることが好ましい。なお、本発明では、いくつかの減量過程のうちで減量が１８％以上の過程を主減量過程と呼ぶ。
【００１８】
本発明において、減量の傾きは、以下の如くして求める。（図１を参照。）
質量Ｍ₀の有機色素を窒素中で１０℃/分の速度で昇温する。昇温に従って、質量は当初微量ずつ減少し、ほぼ直線ａーｂの減量線を描き、ついで急激に減量し始め、１８％以上の減量をほぼ直線ｄ₁ーｄ₂に沿って減量する。これが主減量過程であり、主減量開始温度は、Ｔ₁のことである。その後、ほぼ直線ｃ−ｃで示される減量過程におちつく。直線ｄ₁ーｄ₂と直線ｃ−ｃとの交点における温度をＴ₂、重量をｍ₂とし、初期重量をｍ₁とすれば、ここでいう減量の傾きとは、
【００１９】
【数１】
（ｍ₁-ｍ₂)（％）／（Ｔ₂ーＴ₁)（℃）
【００２０】
で示される値である。この傾きが１０％/℃未満である有機色素を用いると、記録部の横方向の広がりが大きくなり、また、短ビットの形成が困難となるため、高容量化を目的とする短波長用途に向かない。さらに、この主減量過程での総減量は当初質量Ｍ０の好ましくは、３０％以上である。３０％未満であると、良好な記録変調度、記録感度が得られない恐れがある。なお、主減量開始温度は２４０℃〜３４０℃が好ましい。
【００２１】
また、記録再生波長±５ｎｍの波長領域の光に対する記録層単層の屈折率ｎが２〜３であり、消衰係数ｋが０.０３から０.１５であるものが好ましい。また、透明基板上の膜の状態での記録再生波長に最も近い吸収極大が、記録再生波長よりも４０〜８０ｎｍ短波長側にあることが好ましい。溶液での吸収極大が、基板上のスピンコート膜の状態では長波長シフトすることが多いので、透明基板上での吸収極大で判断することが必要である。屈折率ｎが２よりも小さい場合には、十分な光学的変化が得られにくいため、記録変調度が低くなるので好ましくない。また、消衰係数ｋが０．０３未満では記録感度が悪くなる。消衰係数ｋが０.１５を越えると、５０％以上の反射率を得ることが困難となるので好ましくない。波長についても、上記範囲をはずれる場合には、十分な記録変調度と感度を得にくくなる。吸収極大についても、上記範囲をはずれると、記録再生波長近傍での屈折率や消衰係数が適切でないために、十分な記録変調度が得られなくなる。
【００２２】
金属反射層は、記録層を透過したレーザー光を効率良く反射する金属膜であり、６００ｎｍ〜７００ｎｍで反射率が低下しないために、記録再生波長±５ｎｍの波長領域の光の屈折率ｎが０.１〜０.２、消衰係数ｋが３〜５であるものが好ましい。好ましい金属反射膜として、金を主成分とした金属反射膜や、銀を主成分とした金属反射膜が例示できる。特に銀を主成分とした金属反射膜が好ましい。また、対候性の向上のために、銀に、ロジウム、パラジウム、白金、チタン、モリブデン、ジルコニウム、タンタル、タングステン、バナジウム等の添加元素を５原子％以下の範囲で加えてもよい。金属反射層の膜厚は、好ましくは１００ｎｍ以上で、記録層の変形を抑制しすぎたり、記録感度を悪化させすぎない程度の膜厚が好ましい。
【００２３】
反射層の上に、保護層を積層し、記録部の金属反射層の穴の発生や、変形の非対称性を抑制する。保護層としては紫外線硬化樹脂が好ましい。また、通常は、１μｍ以上、好ましくは３μｍ以上の膜厚にして、酸素による硬化抑制等がおこらないようにする。
【００２４】
【実施例】
実施例１
溝深さ１８０ｎｍ、溝幅（溝の半値幅）０．３７μｍ（０.９μｍピッチ）のＵ字案内溝を有するポリカーボネート基板上に下記構造式［３］
【００２５】
【化７】

【００２６】
で示される含金属アゾ色素０.０３６ｇをオクタフルオロペンタノール（ＯＦＰ（沸点１４０℃））３ｇに溶解し、８００ｒｐｍでスピンコートし、８０℃のオーブンで４５分アニール処理し、記録層とした。この色素の減量特性は主減量過程での総減量が３９.８％（主減量開始温度は３１７℃）で、温度差が２.５℃で、減量の傾きは１５.９％/℃であった。なお、熱重量分析はセイコー電子工業製の示差熱天秤（「ＳＳＣ５２００Ｈ」シリーズ「ＴＧ−ＤＴＡ−３２０」）を用いて測定した。
【００２７】
この記録層の上に銀を１００ｎｍの厚さだけスパッタし、その上にＵＶ硬化樹脂（大日本インキ製「ＥＸー３１８」）を約３μｍスピンコートして紫外線ランプで硬化してディスクを作製した。このディスクを６４０ｎｍ又は６８０ｎｍの半導体レーザー評価機（ＮＡ＝０.６）で、線速３ｍ/ｓで溝上に記録したところ、再生パワー０.７ｍＷ、記録周波数を１.５ＭＨｚから３.８ＭＨｚ、ｄｕｔｙ比３０％で変化させ、３.８ＭＨｚの記録時にマークジッターが最小となる記録パワー記録で記録し、マークジッターが１０ｎｓをきる最小ビット長を求めて、その記録膜の高密度記録可能性を評価した（以下、ジッター特性という）。この色素の場合、この記録パワー１４ｍＷで、ジッター特性は０.４μｍであった。
さらに、この記録パワーで、ＣＤ−Ｒの４倍速ＥＦＭ信号（ｎー１）Ｔを入力し、４.８ｍ／ｓ、３.８ｍ／ｓ、３ｍ／ｓ、（以下、ＥＦＭ信号特性と示す）、２.８ｍ／ｓでもジッターがＴの３０％以下で良好な短ビット特性を示した。なお、記録部の膜厚は１２０ｎｍであり、塗布膜の溝深さはＳＴＭで１４０ｎｍのＵ字型であった。この記録層の膜としての吸収極大は６００ｎｍであった。このディスクの記録部の反射率が０.７ｍＷで６０％と十分高かったので、０.７ｍＷで１００万回連続再生したところ、劣化はみられなかった。
【００２８】
この色素の濃度を１ｗｔ％（対溶媒重量）にした以外は上記と全く同じようにして評価した結果を表−１の実施例１の欄に示す。この場合、溝部の膜厚は約１００ｎｍであり、塗布膜の溝深さは１４７ｎｍであった。また、この記録層単層を、キセノンフェードメータで暴露４０時間試験したところ、シアニン系色素は吸収極大の吸光度が０％まで退色したのに対し、この色素は９０％と、良好な耐光性を示した。
【００２９】
実施例２〜３、比較例１〜６
以下に色素の構造をかえて、実施例１と同様にしてディスクを作製し同じ実験をした例を表−１にまとめて示す。各ディスクの溝部の膜厚、塗布膜の溝深さはいずれも、実施例１のそれぞれの値に１０〜２０ｎｍ増減する程度であった。
【００３０】
【表１】

【００３１】
色素の一般式中のＭとしてはいずれもＮｉを用いた。
いずれもＲ１とＲ２とが同じものを用いた。
分解温度は示差熱天秤で測定された主減量過程の開始温度を示す。
ジッター特性は１０ｎｓ以下になるビット長を示す。
ＥＦＭ解像度はＣＤ−Ｒの４倍速用のＥＦＭ信号（ｎ−１）Ｔを入力し、線速４．８ｍ／ｓ、３．８ｍ／ｓ、３．０ｍ／ｓと変えて記録した時、３．０ｍ／ｓでジッターがＴの３０％以上の場合に×印とした。
＊は下記構造式の化合物を示す。
【００３２】
【化８】

【００３３】
＊＊は単膜の吸光度が小さすぎて測定不能であった。
＊＊＊はどのビット長でもジッター２０ｎｓ以上であった。
【００３４】
実施例４
実施例１の色素の溶媒をテトラフルオロプロパノール（沸点１１０℃）に変えた以外は全く同様にしてディスクを作製した。色素濃度は溶媒重量に対し１ｗｔ％としたところ、溝部の膜厚は１２５ｎｍであり、塗布膜の溝深さは１４５ｎｍであった。
このディスクのジッター特性は０.４μｍであり、ＥＦＭ特性は実施例１と同じであった。
【００３５】
比較例７
実施例１の溶媒をジアセトンアルコール（沸点１６６℃）に変えた以外は全く同様にして記録層を形成したところ、記録パワー１４ｍＷでも十分な記録変調度が得られなかった。
【００３６】
【発明の効果】
本発明により、短ビット特性が良好で耐光性に優れた、波長６００〜７００ｎｍの短波長記録に好適な光記録媒体を得ることができる。
【図面の簡単な説明】
【図１】有機色素の主減量過程、主減量過程の総減量、減量の傾きを求める方法を説明するための示差熱天秤のチャート図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium, and more particularly to an optical recording medium capable of recording with a laser beam.
[0002]
[Prior art]
In recent years, an optical recording medium capable of recording / reproducing with a laser beam having a wavelength shorter than 780 nm, for example, 640 nm, has attracted attention as a high-density recording medium. In such a situation, there are various recording media such as a phase change medium having a small wavelength dependency. Among them, an organic dye-based recording medium has a feature that it is inexpensive and easy to process.
[0003]
Cyanine dyes and the like have been proposed as dyes for organic dye-based media for such short wavelength applications, such as JP-A-6-336086, JP-A-7-76169, and JP-A-7-125441. Japanese Laid-Open Patent Publication No. 7-262604. In the recording portion, it is considered that the optical constant absorption and the film thickness decrease due to the thermal decomposition of the dye, the deformation due to the softening of the substrate, and the like are generated as in the CD-R at 780 nm.
[0004]
[Problems to be solved by the invention]
In the above prior art, a large recording modulation degree is obtained by both the decomposition of the dye and the deformation of the substrate during recording. However, since the deformation of the recording portion is too large, crosstalk becomes a big problem. In addition, since the reproduction is performed using a lens having a shorter numerical aperture (NA) of the laser focusing lens in order to increase the density, the laser beam diameter is 780 nm-NA0. Compared to 5, in the case of 640 nm-NA 0.6, the reproduction beam diameter is 1.46 times as high as the degree of condensing. As a result, the temperature rise and the light intensity due to reproduction light irradiation become larger when a short wavelength evaluator (drive) is used, so that a dye that is resistant to reproduction light is particularly required.
[0005]
[Means for Solving the Problems]
The inventors of the present invention have arrived at the present invention as a result of diligently studying a medium that forms a good recording portion in order to realize high-density recording and has little reproduction deterioration.
The gist of the present invention is an optical recording medium for 600 nm to 700 nm in which an organic dye-containing recording layer, a metal reflection layer, and a protective layer are laminated in this order on a transparent substrate, and the recording layer is only one layer. Includes a dye represented by the following general formula 1 (but does not contain a cyanine dye), and the absorption maximum closest to the recording / reproducing light wavelength in the state of the film on the transparent substrate is greater than the recording / reproducing light wavelength. In the method for producing an optical recording medium on the single wavelength side of 40 to 80 nm, a solution obtained by dissolving one or more dyes represented by the following general formula in a fluorinated alcohol having a boiling point of 110 ° C. to 150 ° C. The present invention resides in a method for producing an optical recording medium, characterized in that a recording layer is formed by applying a coating.
[0006]
[Chemical 3]

[0008]
(Wherein, X represents a substituent comprising a diazo group and a conjugate capable electron withdrawing group, Y represents a human Dorokishiru group, a substituted group consisting of carboxyl group, R ^1, R ² is alkyl of 1 to 6 carbon atoms And M ²⁺ represents a divalent ion of nickel, cobalt, or copper.)
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
The recording layer in the present invention is reduced in temperature by absorbing the laser beam for recording, the film thickness is reduced, and the optical characteristics are changed, thereby changing the phase of the return light and changing the reflectance. This is the recording section.
[0010]
In the present invention, a known substrate such as a resin such as polycarbonate, polymethacrylate, amorphous polyolefin, or glass is used as the transparent substrate, and it has a servo guide groove. The groove has a depth of usually 100 to 200 nm, preferably 140 to 200 nm, a groove width of usually 0.3 to 0.4 μm, and a track pitch of usually 0.7 to 1.0 μm. The shape is preferably a U-shaped groove. When the depth of the groove is less than 100 nm, there is a case where sufficient change does not occur at the time of recording and a sufficient degree of recording modulation may not be obtained. If the thickness exceeds 200 nm, the difference in reflectance between the groove and the groove is too large, and in the case of on-groove recording, the reflectance becomes too low, which is not preferable. If the groove width is less than 0.3 μm, it may be difficult to obtain a sufficient tracking error signal intensity. Further, when the groove width exceeds 0.4 μm, the recording portion tends to spread laterally when recording is not preferable. The track pitch is preferably 0.7 to 1.0 μm for the purpose of increasing the capacity. The groove shape can be obtained by optical measurement with a He-Cd laser when the pitch is 1 μm, and can be obtained by measuring the profile with STM or AFM when the track pitch is narrower than that. In Examples described later, it was obtained by STM.
[0011]
The recording layer is obtained, for example, by spin-coating a solution obtained by dissolving an organic dye or the like in a solvent such as ethanol, 3-hydroxy-3-methyl-2-butanone, diacetone alcohol, or fluorinated alcohol. In particular, as the solvent, a fluorinated alcohol having a boiling point of 110 to 150 ° C. is preferably used. When the boiling point is less than 100 ° C., the solvent evaporates at the time of spin coating, so that the coating solution does not move to the outer peripheral side from the radius 40 mm of the disk, the radial thickness distribution becomes extremely large, and good characteristics are obtained. This is not preferable because it may not be present. When the temperature exceeds 170 ° C., it takes time to evaporate and the solvent tends to remain in the film. In such a case, good recording sensitivity is often not obtained. Commonly used solvents other than fluorinated alcohols, such as diacetone alcohol and ethyl cellosolve, have a contact angle with the polycarbonate of the substrate of 30 degrees or more, whereas the fluorinated alcohol is 10 degrees or less, Because of the good wettability of the fluorinated alcohol, the coating solution can sufficiently enter the groove of the narrow track pitch replica, so that a film having good recording characteristics can be formed. In addition, ketone-based or other polar solvents dissolve the polycarbonate of the substrate, so it is necessary to sputter a dielectric film on the substrate or to make expensive polyolefin or glass. This is not preferable because the merit of ease is lost.
[0012]
The film thickness is preferably about 60 to 180 nm at the groove. If it is less than 60 nm, it may be too thin to obtain good recording characteristics. On the other hand, if the thickness exceeds 180 nm, the deformation of the recording portion in the lateral direction and the scanning direction becomes large, so that crosstalk and jitter increase. Moreover, the groove depth of a coating film is 50-180 nm, and it is preferable that it is U-shaped. If the groove depth is less than 50 nm, the tracking error signal amplitude cannot be obtained sufficiently. If the groove depth exceeds 180 nm, the film thickness of the groove is too thin, so that a sufficient recording modulation degree may not be obtained. is there.
[0013]
Examples of organic dyes include cyanine dyes, metal-containing azo dyes, dibenzofuranone, metal-containing indoanilines, and the like. In the present invention, metal-containing azo dyes represented by the general formula [1 ] are particularly preferable. . Examples of X in the above formula include Br, Cl, CF _{3 and the} like. R ¹ and R ² may be a linear alkyl group having 1 to 6 carbon atoms or a branched alkyl group having 3 to 6 carbon atoms. For example, the following pigments can be exemplified.
[0014]
[Chemical formula 5]

[0015]
[Chemical 6]

[0016]
In particular, this type of dye is widely described in Japanese Patent Publication No. 5-67438, etc., and in that case, when limited to high density recording applications, thermal characteristics, molar extinction coefficient as a film, etc. From this request, it is understood that the present invention is limited to specific dyes as exemplified above, and the present invention has been achieved.
The compound is considered to destabilize the diazo bond by substituting an electron-withdrawing group at a position capable of conjugating with the diazo group, and as a result, the weight loss upon decomposition becomes steep. It is considered that it exhibits excellent characteristics.
[0017]
The thermal characteristics of the organic dye constituting the recording layer greatly affect the recording characteristics. In order to obtain sufficient characteristics for short wavelength applications, the weight loss in the main weight loss process in thermogravimetric analysis needs to be sharp with respect to temperature, and was measured at a heating rate of 10 ° C./min. In this case, it is preferable to use an organic dye having a weight loss gradient of 10% / ° C. in the main weight loss process. In the present invention, a process in which weight loss is 18% or more among several weight loss processes is referred to as a main weight loss process.
[0018]
In the present invention, the slope of weight loss is obtained as follows. (See Figure 1)
The organic dye having a mass M ₀ is heated in nitrogen at a rate of 10 ° C./min. As the temperature rises, the mass initially decreases by a small amount, draws a weight loss line of approximately a straight line ab, then starts to decrease rapidly, and the weight loss of 18% or more is reduced substantially along the straight line d ₁ -d ₂ . This is the main weight loss process, and the main weight loss starting temperature is T ₁ . After that, the weight loss process indicated by the straight line cc is almost stopped. If the temperature at the intersection of the straight line d ₁ -d ₂ and the straight line cc is T ₂ , the weight is m ₂ , and the initial weight is m ₁ , the slope of weight loss here is:
[0019]
[Expression 1]
(M ₁ -m ₂ ) (%) / (T ₂ −T ₁ ) (℃)
[0020]
This is the value indicated by. If an organic dye having an inclination of less than 10% / ° C. is used, the lateral spread of the recording part becomes large and it becomes difficult to form a short bit. Not suitable. Furthermore, the total weight loss in this main weight loss process is preferably 30% or more of the initial mass M0. If it is less than 30%, a good recording modulation degree and recording sensitivity may not be obtained. The main weight loss starting temperature is preferably 240 ° C to 340 ° C.
[0021]
Further, it is preferable that the recording layer single layer has a refractive index n of 2 to 3 and an extinction coefficient k of 0.03 to 0.15 with respect to light in the wavelength range of the recording / reproducing wavelength ± 5 nm. The absorption maximum closest to the recording / reproducing wavelength in the state of the film on the transparent substrate is preferably 40 to 80 nm shorter than the recording / reproducing wavelength. Since the absorption maximum in the solution often shifts by a long wavelength in the state of the spin coat film on the substrate, it is necessary to judge by the absorption maximum on the transparent substrate. When the refractive index n is less than 2, it is not preferable because a sufficient optical change is difficult to obtain, and the recording modulation degree becomes low. Further, when the extinction coefficient k is less than 0.03, the recording sensitivity is deteriorated. When the extinction coefficient k exceeds 0.15, it is difficult to obtain a reflectance of 50% or more, which is not preferable. When the wavelength is out of the above range, it is difficult to obtain a sufficient recording modulation degree and sensitivity. If the absorption maximum is out of the above range, the refractive index and extinction coefficient in the vicinity of the recording / reproducing wavelength are not appropriate, so that a sufficient recording modulation degree cannot be obtained.
[0022]
The metal reflection layer is a metal film that efficiently reflects the laser light that has passed through the recording layer. Since the reflectance does not decrease between 600 nm and 700 nm, the refractive index n of light in the wavelength region of the recording / reproducing wavelength ± 5 nm is 0. Those having 0.1 to 0.2 and an extinction coefficient k of 3 to 5 are preferable. As a preferable metal reflection film, a metal reflection film mainly composed of gold and a metal reflection film mainly composed of silver can be exemplified. In particular, a metal reflective film mainly composed of silver is preferable. In order to improve weather resistance, an additive element such as rhodium, palladium, platinum, titanium, molybdenum, zirconium, tantalum, tungsten, or vanadium may be added to silver in a range of 5 atomic% or less. The thickness of the metal reflective layer is preferably 100 nm or more, and is preferably such that the deformation of the recording layer is not suppressed excessively or the recording sensitivity is not deteriorated excessively.
[0023]
A protective layer is laminated on the reflective layer to suppress the formation of holes in the metal reflective layer of the recording unit and deformation asymmetry. As the protective layer, an ultraviolet curable resin is preferable. In general, the film thickness is set to 1 μm or more, preferably 3 μm or more so as not to suppress curing by oxygen.
[0024]
【Example】
Example 1
The following structural formula [3] is formed on a polycarbonate substrate having a U-shaped guide groove having a groove depth of 180 nm and a groove width (half-width of the groove) of 0.37 μm (0.9 μm pitch).
[0025]
[Chemical 7]

[0026]
0.036 g of a metal-containing azo dye represented by the formula (1) was dissolved in 3 g of octafluoropentanol (OFP (boiling point 140 ° C.)), spin-coated at 800 rpm, and annealed in an oven at 80 ° C. for 45 minutes to obtain a recording layer. The weight loss characteristics of this dye were 39.8% total weight loss during the main weight loss process (primary weight loss starting temperature was 317 ° C), the temperature difference was 2.5 ° C, and the slope of weight loss was 15.9% / ° C. It was. The thermogravimetric analysis was performed using a differential thermobalance (“SSC5200H” series “TG-DTA-320”) manufactured by Seiko Denshi Kogyo.
[0027]
On this recording layer, silver was sputtered to a thickness of 100 nm, and a UV curable resin (“EX-318” manufactured by Dainippon Ink, Inc.) was spin-coated on the recording layer by about 3 μm and cured with an ultraviolet lamp to produce a disk. . When this disk was recorded on a groove at a linear velocity of 3 m / s with a 640 nm or 680 nm semiconductor laser evaluator (NA = 0.6), the reproduction power was 0.7 mW, the recording frequency was 1.5 MHz to 3.8 MHz, duty. The ratio is changed at 30%, recording is performed with a recording power recording that minimizes the mark jitter at the time of recording at 3.8 MHz, and the minimum bit length with the mark jitter exceeding 10 ns is obtained, and the high density recording possibility of the recording film is evaluated. (Hereinafter referred to as jitter characteristics). In the case of this dye, the recording power was 14 mW and the jitter characteristic was 0.4 μm.
Furthermore, a CD-R quadruple speed EFM signal (n-1) T is inputted at this recording power, and 4.8 m / s, 3.8 m / s, 3 m / s, (hereinafter referred to as EFM signal characteristics). Even at 2.8 m / s, the jitter was 30% or less of T, and good short bit characteristics were exhibited. Note that the film thickness of the recording portion was 120 nm, and the groove depth of the coating film was a U-shaped 140 nm STM. The absorption maximum as a film of this recording layer was 600 nm. Since the reflectivity of the recording part of this disk was sufficiently high at 60 m at 0.7 mW, no deterioration was observed when it was reproduced continuously 1 million times at 0.7 mW.
[0028]
The results of evaluation in exactly the same manner as described above except that the concentration of this dye was 1 wt% (weight to solvent) are shown in the column of Example 1 in Table-1. In this case, the film thickness of the groove was about 100 nm, and the groove depth of the coating film was 147 nm. In addition, when the recording layer single layer was exposed to a xenon fade meter for 40 hours, the cyanine dye was discolored to a maximum absorbance of 0%, whereas this dye had a good light fastness of 90%. Indicated.
[0029]
Examples 2 to 3 and Comparative Examples 1 to 6
Table 1 summarizes examples in which the same experiment was performed by changing the structure of the dye and producing a disk in the same manner as in Example 1. The film thickness of the groove portion of each disk and the groove depth of the coating film were both increased or decreased by 10 to 20 nm from the respective values in Example 1.
[0030]
[Table 1]

[0031]
Ni was used as M in the general formula of the dye.
In either case, the same R1 and R2 were used.
The decomposition temperature indicates the starting temperature of the main weight loss process measured with a differential thermobalance.
The jitter characteristic indicates a bit length of 10 ns or less.
The EFM resolution is 4 × CD-R EFM signal (n−1) T input, and the linear velocity is changed to 4.8 m / s, 3.8 m / s, and 3.0 m / s. X was marked when the jitter was 30% or more of T at 0.0 m / s.
* Represents a compound having the following structural formula.
[0032]
[Chemical 8]

[0033]
** cannot be measured because the absorbance of the single membrane was too small.
*** has a jitter of 20 ns or more at any bit length.
[0034]
Example 4
A disk was produced in exactly the same manner except that the solvent of the dye of Example 1 was changed to tetrafluoropropanol (boiling point 110 ° C.). When the dye concentration was 1 wt% with respect to the solvent weight, the groove thickness was 125 nm and the groove depth of the coating film was 145 nm.
The jitter characteristic of this disk was 0.4 μm, and the EFM characteristic was the same as in Example 1.
[0035]
Comparative Example 7
When a recording layer was formed in the same manner except that the solvent of Example 1 was changed to diacetone alcohol (boiling point 166 ° C.), sufficient recording modulation could not be obtained even at a recording power of 14 mW.
[0036]
【The invention's effect】
According to the present invention, it is possible to obtain an optical recording medium having good short bit characteristics and excellent light resistance and suitable for short wavelength recording with a wavelength of 600 to 700 nm.
[Brief description of the drawings]
FIG. 1 is a chart of a differential thermal balance for explaining a method for obtaining a main weight loss process of an organic dye, a total weight loss of the main weight loss process, and a slope of the weight loss.

Claims (6)

In an optical recording medium for 600 nm to 700 nm in which an organic dye-containing recording layer, a metal reflective layer, and a protective layer are laminated in this order on a transparent substrate , there is only one recording layer, and the recording layer is represented by the following general formula 1. The absorption maximum closest to the recording / reproducing light wavelength in the state of the film on the transparent substrate is 40 to 80 nm single wavelength than the recording / reproducing light wavelength. In the method for producing an optical recording medium on the side, recording is performed by applying a solution obtained by dissolving one or more dyes represented by the following general formula in a fluorinated alcohol having a boiling point of 110 ° C to 150 ° C. A method for producing an optical recording medium, comprising forming a layer.

(In the formula, X represents a substituent composed of an electron-withdrawing group that can be conjugated with a diazo group, Y represents a substituent composed of a hydroxyl group and a carboxyl group, and R ¹ and R ² are alkyl groups having 1 to 6 carbon atoms. M ²⁺ represents a divalent ion of nickel, cobalt or copper.)   2. The thermogravimetric analysis of the dye forming the recording layer, wherein the slope of weight loss with respect to temperature in the main weight loss process is 10% / ° C. or more, and the total weight loss in the main weight loss process is 30% or more. Manufacturing method of optical recording medium.   3. The method of manufacturing an optical recording medium according to claim 1, wherein the groove thickness of the recording layer is 60 nm to 180 nm, the groove depth of the coating film is 50 nm to 200 nm, and the groove is a U-shaped groove. .   4. The optical recording medium according to claim 1, wherein the guide groove of the substrate has a track pitch of 0.7 to 1 [mu] m, and the half width of the groove width is 0.3 to 0.4 [mu] m. Manufacturing method.   The method for producing an optical recording medium according to any one of claims 1 to 4, wherein the metal reflective layer is mainly composed of silver.   The method for producing an optical recording medium according to claim 1, wherein the protective layer is an ultraviolet curable resin.

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