JPH07161069A - Optical recording medium - Google Patents

Abstract

PURPOSE:To form a satisfactory minute recording part almost free from a rim, to ensure small bit length jitter and to attain satisfactory recording sensitivity and recording characteristics as an optical recording medium for high linear velocity and short wavelength recording. CONSTITUTION:This optical recording medium has an org. dye layer for recording and reproduction with laser light of 630-690nm wavelength on the substrate. The spectral absorption max. of the org. dye layer is in the range of 550-730nm and the thickness of the layer is in the range of 200-800Angstrom . The real part of the complex index of refraction of the layer at the recording or reproduction wavelength is 1.6-3 and the imaginary part is >=1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium, and more particularly to an optical recording medium recordable by laser light.

[0002]

2. Description of the Related Art In recent years, attention has been paid to shortening the oscillation wavelength of laser light for high density recording, and 780 nm and 830 nm
There is a demand for an optical recording medium capable of recording and reproducing with a laser beam having a shorter wavelength. Optical recording media proposed in this situation include magneto-optical recording media, phase change recording media, chalcogen oxide optical recording media, and organic dye-based optical recording media. Among these, the organic dye-based optical recording medium is considered to be superior in that it is inexpensive and easy to process.

By the way, as an organic dye-based optical recording medium, as a recordable compact disc, a type in which a metal layer having a high reflectance is laminated on a thin organic dye layer is widely known. The structure has poor recording sensitivity and is disadvantageous for recording at high linear velocity. In addition, since the substrate is deformed in addition to the dye during recording, there is a problem that the bit length variation causes a large variation in the bit length and a large jitter.

On the other hand, a great deal of research has been conducted on the recording system using an organic dye single layer, including the film surface incidence system of recording / reproducing light, and a part thereof has been put to practical use as an optical recording medium for 780 nm. There is. However, for short wavelength applications, JP-A-4-74690 and JP-A-4-23 are available.
Although various proposals such as JP-A No. 8036 and JP-A No. 5-38878 have been made, light resistance, environment resistance and the like are completely inadequate, and problems unique to short wavelength applications have not been solved at all. The current situation is that there are none.

[0005]

Conventionally, there has been a problem that the formation of a rim caused by recording is disadvantageous for short wavelength applications, that is, high density recording by short bit recording, with respect to an organic dye-based optical recording medium. . Further, it is difficult to obtain sufficient recording sensitivity and recording characteristics in high linear velocity recording of 10 m / s or more.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have formed a fine recording portion having no rim in order to realize high density recording, and have a wavelength 630 having sufficient characteristics even at high linear velocity recording. The present invention has been achieved as a result of intensive studies on a medium and conditions suitable for recording at a short wavelength of ˜690 nm. The gist of the present invention is an optical recording medium having an organic dye layer on a substrate for recording and reproducing with a laser beam having a wavelength of 630 to 690 nm, and the spectral absorption maximum of the organic dye layer is in the range of 550 to 730 nm. A short wavelength characterized in that the film thickness of the organic dye layer is in the range of 200 to 800Å, the real part of the complex refractive index of the organic dye layer at the recording / reproducing wavelength is 1.6 to 3, and the imaginary part is 1 or more. It exists in an optical recording medium for recording. Hereinafter, the present invention will be described in detail.

The optical recording medium of the present invention has a structure in which an organic dye layer is provided on a substrate. Depending on the purpose, a thin ceramic layer may be formed on the organic dye layer or an ultraviolet curable resin may be used. You may laminate. In addition, so-called air sandwich type bonding may be performed in which two media having an organic dye layer provided on a substrate are bonded so that the organic dye layers face each other via a spacer. As the substrate, a polycarbonate substrate, an amorphous polyolefin substrate, a glass substrate, etc.
A known transparent material having a small birefringence is preferably used.

The organic dye layer is usually formed by coating an organic dye dissolved in a solvent on a substrate and drying it, or by vacuum depositing the organic dye on the substrate. As the solvent in the case of the coating method, for example, in the case of a polycarbonate substrate, those which do not attack the polycarbonate substrate such as ethanol, 3-hydroxy-3-methyl-2-butanone, diacetone alcohol and fluorine-based alcohol are preferably used. , In the case of polyolefin substrate, chloroform,
A polar solvent such as methyl ethyl ketone is preferably used.

The organic dye layer has a spectral absorption maximum of 550.
It is necessary to be in the range of nm to 730 nm. 55
If the absorption maximum is in the wavelength region shorter than 0 nm, sufficient sensitivity cannot be obtained in the layer structure of the present invention, or
A good reproduction signal cannot be obtained. The same applies to the organic dye layer having the absorption maximum on the longer wavelength side than 730 nm. Particularly, it is preferable that the absorption maximum is in the range of ± 40 nm of the recording / reproducing wavelength.

In the organic dye layer, the real part of the complex refractive index at the recording / reproducing wavelength is 1.6 to 3, and the imaginary part must be 1 or more. In the constitution of the medium of the present invention, in order to obtain good recording contrast, the unrecorded portion of the dye on the substrate must have a certain reflectance. The reflectance must be 10% or more at the recording / reproducing wavelength. If the real part is less than 1.6, sufficient contrast cannot be obtained, and if it exceeds 3, the change in reflectance due to the change in film thickness becomes large, and the process margin tends to be narrowed.
When the imaginary part is less than 1, sufficient reflectance cannot be obtained, light absorption is small, and good sensitivity cannot be obtained.

The thickness of the organic dye layer is 200Å-80
It must be in the range of 0Å. When the film thickness of the organic dye layer is less than 200 Å, the coating film is formed only in the groove, which makes it difficult to record between the grooves. On the other hand, when it exceeds 800 Å, the rim becomes thicker and the asymmetry of the recording portion in the laser beam scanning direction is emphasized, so that the jitter tends to be deteriorated in the bit length recording. The organic dye used in the organic dye layer of the present invention is preferably a metal-containing azo dye or a phthalocyanine dye. As the metal-containing azo dye, the following general formula (1)

[0012]

[Chemical 1]

(In the formula, R ¹ and R ² are each independently a hydrogen atom or an optionally substituted C ¹ -C 1
It represents an alkyl group having 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or a cycloalkyl group having 3 to 10 carbon atoms. R ³ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or 1 to 1 carbon atoms.
6 alkylsulfonyl group, an alkylcarbonyl group having 2 to 7 carbon atoms, a halogen atom, a formyl group, -CR ⁵ = C
(CN) R ⁶ (wherein R ⁵ is a hydrogen atom or a carbon number 1
It represents 6 alkyl group, R ⁶ represents a cyano group or an alkoxycarbonyl group having 2 to 7 carbon atoms. ), Nitro group, -Z-Ar (wherein, Z is a single bond, -SCH ₂ -,
Represents —SO ₂ — or —SO ₂ CH ₂ —, and Ar represents an aromatic ring optionally substituted with a nitro group. ), A trifluoromethyl group, a trifluoromethoxy group, a cyano group, an alkoxycarbonyl group having 2 to 7 carbon atoms, an alkoxycarbonylalkyl group having 3 to 7 carbon atoms, or an alkylthio group having 1 to 6 carbon atoms. R ⁴ is an alkyl group having 1 to 6 carbon atoms,
An alkoxy group having 1 to 6 carbon atoms, a halogen atom, a nitro group, a cyano group, an alkylsulfonyl group having 1 to 6 carbon atoms,
It represents an alkoxycarbonyl group having 2 to 7 carbon atoms or a thiocyanate group. M is Ni, Co, Zn, Fe, Ru,
Represents a transition metal element such as Rh and Pd. The metal-containing azo dye represented by the formula (1) is preferable. Of these, M is Ni,
R ¹ and R ² are CH ₃ , C ₂ H ₅ , C ₃ H ₇ or C ₄ H ₉ , R
⁴ is OCH ₃ , CH ₃ Or OC ₂ H ₅ and R ⁴ are CH ₃ and C
F ₃ , CH = C (CN) ₂ , C (CH) = C (CN) ₂ , SC
Those which are ₂ F ₅ or SC ₃ F ₇ are preferred. Further, as the phthalocyanine dye, the following general formula (2)

[0014]

[Chemical 2]

(In the formula, R ⁷ to R ¹⁰ each independently represent a hydrogen atom or a carbon atom which may have a substituent.
6 represents an alkoxy group, M'is a central metal, and C is
It represents u, Ni, Co, Fe, Zn, Sn, VO or Pd. Further, M'may not be present. ) The phthalocyanine dyes represented by (4) are preferable. Recording and reproduction are performed using the optical recording medium of the present invention by injecting laser light from the substrate side. The organic dye layer absorbs the incident laser light and generates heat, and when it reaches a temperature exceeding the main weight loss onset temperature, it begins to decompose into low molecular weight fragments, and as a result, recesses are formed. Since a slight amount of dye remains in this recess or there is almost no dye, the reflectance decreases when the reproducing light is irradiated, and it is detected as a recording portion. Here, the main weight loss onset temperature of the organic dye in the recording layer is obtained as follows. Figure 4
FIG. 6 is a chart of a differential thermal balance for showing a method of determining the main raw material starting temperature T. 1 organic pigment of mass M ₀
The temperature is raised at 5 ° C / minute. As the temperature rises, the mass initially decreases by a small amount and draws a straight line ab. Then, the weight reduction is started rapidly, and the weight loss of 40% or more is reduced substantially along the straight line d ₁ -d ₂ . The main weight loss starting temperature of the present invention is defined by the temperature T at the intersection of the straight line a-b and the line d ₁ -d _2.

In the examples, a differential thermal balance (Seiko Denshi Kogyo) SSC5200H series TG-DTA-320 was used to measure a sample weight of 5 mg in a nitrogen atmosphere at a temperature rising rate of 15 C / min. The starting temperature of the process showing the weight loss of not less than% was taken as the intersection of the contact points of the weight loss process.
In the present invention, the main weight loss onset temperature of the organic dye in the recording layer, which is determined by such a method, is preferably in the range of 250 ° C to 370 ° C. If it is lower than 250 ° C, it may deteriorate due to repeated regeneration. On the other hand, if the temperature exceeds 370 ° C., the recording sensitivity tends to be poor and high linear velocity recording tends to be difficult.

The shape of the recording portion greatly differs depending on the dye used, and the rim becomes thinner as the film thickness is made thinner, but the asymmetry of the recording portion is not always improved. Among them, particularly in an optical recording medium having an organic dye layer composed of the metal-containing azo dye represented by the general formula (1) or the phthalocyanine dye represented by the general formula (2), most of the rim is formed. However, it is preferable because it exhibits good jitter characteristics even at high linear velocity recording.

[0018]

【Example】

Example 1 The following structural formula (3) was formed on a polycarbonate substrate having a track pitch of 1.1 μm.

[0019]

[Chemical 3] A metal-containing azo dye represented by (main weight loss starting temperature 279
An optical recording medium (optical disk) was manufactured by applying a solution prepared by dissolving 1.0% by weight of a fluoroalcohol solvent in a spin coating method. The thickness of the organic dye layer is 400Å, 680
The real part (n) and the imaginary part (k) of the complex refractive index in nm are 1.75 and 1.17, respectively, and the spectral absorption maxima are 710 nm and 6, respectively.
It was 40 nm. When the obtained optical disk was evaluated with an evaluation machine (Pulstec Co., numerical aperture NA 0.5) using a 680 nm semiconductor laser, groove-to-groove recording was 10 m /
s, 7.16 MHz, duty ratio 50%, C / N was 53 dB (recording power 5 mW), and the best bit length jitter was 1 ns.

Example 2 The following structural formula (4) was used as an organic dye.

[Chemical 4] Metal-containing azo dye represented by (main weight loss starting temperature 365
An optical disk was manufactured in the same manner as in Example 1 except that (.degree. C.) was used. The thickness of the organic dye layer is 700Å, 680n
The real part (n) and the imaginary part (k) of the complex refractive index at m are n = 1.75 and k = 1.3, respectively, and the spectral absorption maximum is 640 nm.
And 720 nm. The obtained optical disk was used in Example 1.
When evaluated in the same manner as in, C / N was 56.4d.
B (recording power 7 mW), best bit length jitter is 1 n
It was s.

Example 3 The following structural formula (5) was used as an organic dye.

[Chemical 5] Metal-containing azo dye represented by (main weight loss starting temperature 298
An optical disk was manufactured in the same manner as in Example 1 except that (.degree. C.) was used. The thickness of the organic dye layer is 400Å, 680n
The real part (n) and the imaginary part (k) of the complex refractive index at m are n = 2.11 and k = 1.49, respectively, and the spectral absorption maximum is 620n.
m and 690 nm. 680 on the obtained optical disk
When pulse recording was performed at 10 m / s for 330 ns with the same evaluation apparatus as in Example 1 using a semiconductor laser of nm,
As shown in the electron micrograph of FIG. 2, a good rim-shaped recording portion was obtained, and the groove-to-groove recording was 10 m / s, 7.16 MHz,
When recording was performed at a duty ratio of 50%, the best bit length jitter was 7 ns (recording power 7 mW).

Example 4 An optical disk was manufactured by vacuum-depositing metal-free unsubstituted phthalocyanine (main weight reduction starting temperature 320 ° C.) on a polycarbonate substrate having a track pitch of 1.1 μm. The film thickness of the organic dye layer is 800Å, and the real part (n) and the imaginary part (k) of the complex refractive index at 680 nm are n = 2.4 and k =, respectively.
1.2, the spectral absorption maximum was 630 nm. A pulse recording of 10 m / s and 330 ns was performed on the obtained optical disc with the same evaluation machine as in Example 1 using a semiconductor laser of 680 nm. As a result, as shown in the electron micrograph of FIG. was gotten.

Comparative Example 1 An optical disk was manufactured under the same conditions as in Example 3, except that the metal-containing azo dye used in Example 3 was dissolved in a fluoroalcohol solvent at 1.5% by weight. The thickness of the organic dye layer is 900
Å, the real part (n) and the imaginary part (k) of the complex refractive index at 680 nm were n = 2.1 and k = 1.5, respectively, and the spectral absorption maximums were 620 nm and 690 nm. When recording and evaluation were performed in the same manner as in Example 3, as shown in the electron micrograph of FIG. 3, a thick rim asymmetric recording portion with a bad bit shape was obtained, and recording between grooves was 10 m / s, 7.16 MHz. ,
When recording was performed at a duty ratio of 50%, the best bit length jitter was 20 ns.

Comparative Example 2 As the organic dye, the following structural formula (6)

[Chemical 6] Metal-containing azo dye represented by (main weight loss starting temperature 271
An optical disk was manufactured in the same manner as in Example 1 except that (.degree. C.) was used. The thickness of the organic dye layer is 700Å, 680n
The real part (n) and the imaginary part (k) of the complex refractive index at m are n = 0.88 and k = 0.83, respectively, and the spectral absorption maximum is 780n.
It was m. An attempt was made to evaluate the obtained optical disk with the same evaluation machine as in Example 1, but good recording could not be achieved.

Comparative Example 3 The following structural formula (7) was used as the organic dye.

[Chemical 7] Phthalocyanine dye shown by (main weight loss starting temperature 38
An optical disk was manufactured in the same manner as in Example 1 except that (7 ° C.) was used. The thickness of the organic dye layer is 900Å, 680
The real part (n) and the imaginary part (k) of the complex refractive index in nm are n = 1.9 and k = 0.6, respectively, and the spectral absorption maximum is 780 nm.
Met. An attempt was made to evaluate the obtained optical disk with the same evaluation machine as in Example 1, but good recording could not be achieved.

[0026]

The optical recording medium of the present invention has a good minute recording portion with almost no rim, little bit length jitter, and sufficient recording sensitivity and recording characteristics as an optical recording medium for high linear velocity short wavelength recording. Very useful as it can be achieved.

[Brief description of drawings]

FIG. 1 is a photograph showing a fine pattern formed on a substrate in Example 3 of the present invention.

FIG. 2 is a photograph showing a fine pattern formed on a substrate in Example 4 of the present invention.

FIG. 3 is a photograph showing a fine pattern formed on a substrate in Comparative Example 1 of the present invention.

FIG. 4 is a chart of a differential thermal balance for determining a main weight loss onset temperature of a dye.

Continuation of the front page (72) Inventor Towa, Horie 1000, Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Sanryo Kasei Co., Ltd.

Claims (3)

[Claims] 1. An optical recording medium having an organic dye layer on a substrate for recording / reproducing with a laser beam having a wavelength of 630 to 690 nm, wherein the organic dye layer has a spectral absorption maximum of 550 to 7.
It is in the range of 30 nm and the film thickness of the organic dye layer is 200 to 8
An optical recording medium for short wavelength recording, wherein the real part of the complex refractive index of the organic dye layer at the recording / reproducing wavelength is 1.6 to 3 and the imaginary part is 1 or more in the range of 00Å. 2. The optical recording medium according to claim 1, wherein the organic dye is a metal-containing azo dye or a phthalocyanine dye. 3. The main weight loss onset temperature of the organic dye is 250 to 3.
The optical recording medium according to claim 1 or 2, which has a temperature range of 70 ° C.