JP2925121B2 - Optical recording medium and optical recording method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording medium and an optical recording method.

<Prior Art> Various write-once optical recording disks using a dye as a recording layer have been developed.

However, since the dye is photobleached by singlet oxygen etc., in order to improve the light resistance, the fact that a quencher is added,
Various proposals have been made by the present inventors (JP-A-59-5579).
No. 4, No. 59-55795, No. 60-159087, No. 60-162611
No., No. 60-203488, No. 60-163243).

<Problem to be Solved by the Invention> An object of the present invention is to provide an optical recording medium and an optical recording method that can perform recording and reproduction in good accordance with the CD standard by using a novel optical recording method having excellent light resistance. It is in.

Such an object is achieved by the following (1) to (3) of the present invention.

(1) A light-absorbing dye having an absorption maximum at 600 to 900 nm and an azo dye having an absorption maximum at 350 to 600 nm on a substrate, wherein the light-absorbing dye has a condensed ring. A recording layer having at least two kinds of cyanine dyes having a renin ring and having an extinction coefficient k of 0.05 to 0.2 at a wavelength of 700 to 900 nm for recording light and reproduction light, and a reflective layer and a protective layer on the recording layer An optical recording medium on which is laminated.

(2) The optical recording medium according to (1), wherein the recording layer further contains a quencher.

(3) An optical recording method for performing recording by irradiating the optical recording medium of (1) or (2) with recording light.

<Action> In the present invention, an azo dye having a shorter wavelength is added to a light-absorbing dye having absorption at a longer wavelength to improve light resistance.

In general, it is known that when some azo dyes are used in a mixture with, for example, an anthraquinone dye, a phenomenon called catalytic fading or abnormal fading occurs, and photofading of the azo dye is remarkably accelerated ("" Chemistry of Functional Dyes ”, CMC, 1981, pp. 74-76.

In the present invention, the catalytic fading is actively utilized to oxidize the azo dye preferentially over the light absorbing dye, thereby extending the life of the light absorbing dye.

As a result, unexpected improvement in light resistance has been achieved.

Catalytic fading has been conventionally observed variously in development,
This has been suppressed by a singlet oxygen quencher (see above), but the idea of actively using this phenomenon to improve the life of the dye and the medium has been proposed. That was not there.

<Specific Configuration> Hereinafter, a specific configuration of the present invention will be described in detail.

 The optical recording medium 1 of the present invention is a so-called contact type.

The contact-type optical recording medium 1 is, as shown in FIG.
A recording layer 3 containing a dye is provided on a substrate 2.
To form a reflective layer 4, and more preferably, a protective film 5.

 The recording layer contains a light absorbing dye.

The light absorption dye used has an absorption maximum of 600 to 900 nm, more preferably 700 to 900 nm.

Then, a cyanine dye having an indolenine ring which may have a condensed ring is used.

Further, a quencher may be mixed with the light absorbing dye.
Further, an ion binder of a dye cation and a quencher anion may be used as the light absorbing dye.

As the quencher, metal complexes such as acetylacetonate-based, bisdithio-α-diketone-based and bisphenyldithiol-based bisdithiol-based, thiocatechol-based, salicylaldehyde oxime-based, and thiobisphenolate-based metal complexes are preferable.

 Further, an amine-based quencher is also suitable.

The dye constituting the conjugate is preferably a cyanine dye having an indolenine ring, and the quencher is preferably a metal complex dye such as a bisphenyldithiol metal complex.

Details of preferred dyes, quencher and conjugates are described in JP-A-59-24692, JP-A-59-55794, and JP-A-59-55795.
Nos. 59-81194, 59-83695, 60-18387,
No. 60-19586, No. 60-19587, No. 60-35054, No. 60
-36190, 60-36191, 60-44554, 60-445
No. 55, No. 60-44389, No. 60-44390, No. 60-47069
No. 60-20991, No. 60-71294, No. 60-54892,
No. 60-71295, No. 60-71296, No. 60-73891, No. 60
No. 73892, No. 60-73893, No. 60-83892, No. 60-854
No. 49, No. 60-92893, No. 60-159087, No. 60-162611
No. 60-203488, No. 60-201988, No. 60-234886
No. 60-234892, No. 61-16894, No. 61-11292,
No. 61-11294, No. 61-16891, No. 61-8384, No. 61-
No. 14988, No. 61-163243, No. 61-210539, Japanese Patent Application No. 60
-54013, JP-A-62-30088, JP-A-62-32132 and 62
No.-31792, "Functional Dye Chemistry" and the like.

The quencher may be added separately from the light-absorbing dye or may be added in the form of a conjugate. However, the quencher may be added in an amount of 1 mol or less, particularly about 0.05 to 0.5 mol, per 1 mol of the total light-absorbing dye. Is preferred.

 Thereby, the light resistance is further improved.

In the present invention, a dye having an absorption maximum at 350 to 600 nm, especially 350 to 550 nm, is mixed with two or more of these indolenine cyanine dyes as light absorbing dyes or a quencher.

As the dye to be used, any dye having the above-mentioned maximum absorption wavelength may be used. In particular, the dye has substantially no absorption at a wavelength of 700 to 900 nm, and has a real part (refractive index n) of a complex refractive index at a wavelength of use. , Respectively, are preferably 2.8 or less. Then, two or more of these are used in combination.

By having such optical characteristics, photobleaching can be selectively performed by the catalytic action of the light absorbing dye.

Such photobleachable dyes are particularly azo dyes such as mono, bis and trisazo.

 The following azo dyes are particularly preferable.

In addition, the following azoic dyes or diazo compounds are also suitable.

These photobleachable dyes having short-wavelength absorption characteristics may be mixed in an amount of about 0.01 to 0.4 mol, particularly about 0.02 to 0.2 mol, per 1 mol of the total of two or more light-absorbing dyes.

The recording layer is composed of two or more types of light-absorbing dyes and a photobleachable dye, but may further contain a resin or the like.

Although there is no particular limitation on the method of forming the recording layer, in the present invention,
It is preferable to form the layer by coating, because the degree of freedom and easiness in the selection of the dye, the design of the medium, and the production are further expanded.

Various solvents such as ketone, ester, ether, aromatic, alkyl halide, and alcohol can be used for coating the recording layer, and the degree of freedom in selecting the solvent is large. Spin coating or the like may be used for application.

As shown in FIG. 1, when a close contact type medium is used,
The extinction coefficient (imaginary part of the complex refractive index) k of the recording layer 3 at the wavelength of the recording light and the reproduction light is 0.05 to 0.2.

When k is less than 0.05, the absorptivity of the recording layer decreases, and it is difficult to perform recording with normal recording power.

On the other hand, if k exceeds 0.2, the reflectivity falls below 60%, making it difficult to perform reproduction according to the CD standard.

In this case, when k is 0.05 to 0.15, a very favorable result is obtained.

The refractive index (the real part of the complex refractive index) n is 2.1 to 4.0,
More preferably, it is 2.2 to 3.3.

If n <2.1, the reflectivity tends to decrease, and it is difficult to reproduce data according to the CD standard. Also, in order to make n> 4.0,
It becomes difficult to obtain raw material dyes.

In the present invention, the photobleachable dye having absorption at a short wavelength is 60
Since n and k of 0 to 900 nm, especially 700 to 900 nm are small,
What has n and k in the above range may be selected from the above two or more light absorbing dyes, two or more light absorbing dye-quencher mixtures, and two or more dye-quencher conjugates.

In addition, k for the recording light and the reproduction light of the light absorbing dye
Varies from 0 to about 2 depending on its skeleton and substituents. For example, when a dye having a k of 0.05 to 0.2 is selected, there are limitations on its skeleton and substituents. For this reason,
In some cases, the coating solvent is limited, or the coating cannot be performed depending on the substrate material. Alternatively, gas phase film formation may not be possible. In addition, when a new molecular design is performed, great effort is required for design and synthesis.

On the other hand, according to the experiments of the present inventors, k of the mixed dye layer containing two or more dyes is a value substantially corresponding to the mixing ratio according to k of the dye layer composed of each dye used alone. It turned out to be. Therefore, in the present invention, the recording layer is formed by dissolving two or more kinds of cyanine dyes.

At this time, k is almost proportional to the mixing ratio in the mixed system of most of the dyes. That is, assuming that the mixture fraction of i kinds of dyes and k are Ci and ki, respectively, k
Becomes almost ΣCiki. Therefore, by mixing the dyes having different k with each other while controlling the mixing ratio, k = 0.05 to 0.15
Can be obtained. Therefore, a dye to be used can be selected from a very wide range of dye groups.

This can be applied to the improvement of the wavelength dependency. The wavelength of a semiconductor laser is usually in the range of ± 10 nm, and commercially available CD
For players, 70% reflectivity in the 770 to 790 nm range
It is necessary to secure more. In general, the k value of a dye often has a large wavelength dependence. Even if the k value is an appropriate value at 780 nm, it often deviates greatly at 770 or 790 nm. In such a case, by mixing the second dye, it can be set so that appropriate n and k values are always obtained in the range of 780 ± 10 nm.

As a result, there is no limitation on the film forming method such as restrictions on the coating solvent and the like, and it is also possible to use an inexpensive dye that is easy to synthesize, to use a dye having good characteristics, and to use a hardly soluble dye. be able to.

When the recording layer is a mixed layer of a light absorbing dye, the light absorbing dye to be used may be selected from those in the range of n = 1.9 to 6.5 and k = 0 to 2.

When measuring n and k, a recording layer is formed on a predetermined transparent substrate to a thickness of, for example, about 400 to 800 ° under actual conditions to prepare a measurement sample. Next, the reflectance through the substrate or from the recording layer side is measured. The reflectance is measured by specular reflection (about 5 °) using the recording / reproducing light wavelength. Also, the transmittance of the sample is measured. From these measured values, for example, n and k may be calculated in accordance with Kyoritsu Zensho “Optics” Kozo Ishiguro P-168 to 178.

It is preferable that the thickness of such a recording layer be 1000 to 1500 °. Outside of this range, the reflectivity decreases, making it difficult to perform CD standard reproduction.

In such a recording layer 3, as shown in FIG.
The reflection layer 4 is provided in close contact with the substrate.

As the reflective layer, a high-reflectance metal such as Au, Ag, Cu, or Pt may be used, and it is particularly preferable to use Au.

The thickness of the reflective layer may be 500 mm or more, and may be formed by vapor deposition, sputtering, or the like. As a result, the reflectance of the unrecorded portion of the medium through the substrate can be 60% or more, particularly 70% or more.

The substrate or substrate 2 on which the recording layer is formed is substantially transparent (preferably transparent) to recording light and reproduction light (laser light of about 600 to 900 nm, particularly about 700 to 900 nm, particularly semiconductor laser light, especially 780 nm). (80% or more) resin or glass. This enables recording and reproduction from the back side of the substrate.

The substrate has a disk shape of a normal size, and when used as a CD, has a thickness of about 1.2 mm and a diameter of about 80 to 120 mm.

In this case, a resin is preferably used as the base material, and a thermoplastic resin such as a polycarbonate resin, an acrylic resin, an amorphous polyolefin, and TPX is preferable.

It is preferable that a groove for tracking is formed on the recording layer forming surface of the substrate.

Further, the tracking portion may be provided with unevenness for an address signal.

Note that a resin layer (not shown) may be provided on the base by, for example, the 2P method, and the resin layer may be provided with a tracking groove or an address signal unevenness.

The material of the resin constituting the resin layer is not particularly limited, and may be appropriately selected from known resins used in the so-called 2P method. Usually, a radiation-curable compound is used.

 Further, a protective film 5 is provided on the reflective layer 4.

The protective film may be formed of various resin materials such as an ultraviolet curable resin, for example, to a thickness of generally about 10 to 100 μm.
The protective film 5 may be in the form of a layer or a sheet.

To perform recording or additional recording on the contact-type optical recording medium 1 having such a configuration, recording light of, for example, 780 nm is irradiated through the base 2 in a pulsed manner.

Thereby, the recording layer 3 absorbs light and generates heat, and at the same time, the base 2 is also heated. As a result, in the vicinity of the interface between the substrate 2 and the recording layer 3, melting or decomposition of the recording layer material such as a dye occurs, and pressure is applied to the interface between the recording layer 3 and the substrate 2, and the bottom wall and the side wall of the groove 23 are removed. Deform.

In this case, since the melted or decomposed material of the recording layer 3 has no place to go in the closed space, a part thereof rises toward the land portion 21 of the base, and the rest remains at the bottom of the groove 23. In this manner, the decomposed material layer 61 containing the decomposed material of the recording material
However, it usually remains in a shape that covers the bottom and boundary of the groove 23.

The material of the decomposed material layer 61 is generally a material that does not substantially include the base material, and is composed of a decomposed material of the recording layer material or a mixture of the decomposed material of the recording layer material and the recording layer material.

The decomposition layer 61 is usually about 30 to 90% of the thickness of the recording layer 3.

Then, usually, a void 63 is formed on the decomposed substance layer 61 at the interface with the reflective layer 4, and the decomposed substance layer 61 and the void 63 are formed in the pit portion 6.

The gap 63 is usually about 10 to 70% of the thickness of the recording layer 3.

In such a recording process, the base 2 may not be deformed, but the pit portion 6 of the base 2 is generally dented by the pressure during heating. The amount of dent of the substrate is larger as the size of the pit portion is larger, usually 0 to 30.
The depth is about 0 mm.

In addition, the recording layer material or its decomposition product may remain on the gap 63 with a very small film thickness in close contact with the reflection layer 4.

The power of the recording light is about 5 to 9 mW, and the substrate linear velocity is about 1.2 to 1.4 m / s.

After the pit portion 6 is formed in this way, for example, 78
When the reproduction light of 0 nm is irradiated through the base, a phase difference of light is generated by the pit portion 6, and the reflectance is reduced by 60% or more.

On the other hand, since the unrecorded portion has a high reflectance of 60% or more, particularly 70% or more, it can be reproduced according to the CD standard.

In the above, the case of a single-sided recording medium has been described, but a double-sided recording medium can also be obtained by forming a recording layer and a reflective layer on a pair of substrates and integrating them via a protective film or the like.

<Example> Example 1 Recording layers Nos. 1, 2, and 3 in Table 1 below were formed on a polycarbonate resin substrate having a continuous group and a thickness of 120 mm and a thickness of 1.2 mm. On this recording layer, Au was deposited to a thickness of 1000 mm by vapor deposition to form a reflective layer, and an ultraviolet-curable resin containing an oligoester acrylate was applied, followed by ultraviolet curing to form a 50 μm-thick protective film. Disk samples were obtained.

The recording layer was formed by spin coating while rotating the substrate at 500 rpm. As a coating solution, a 1.5 wt% solution of dichloroethane was used. The thickness of the dye layer after drying was 1300 mm.

Table 1 shows the 780 nm refractive index (n) and extinction coefficient (k) of the recording layer of each sample.

n and k were determined by forming a solution containing the above dye on a measurement substrate to a dry film thickness of 600 ° to form a test recording layer, and measuring n and k of the test recording layer. This measurement is based on “Optics” (Kozo Ishiguro, Kyoritsu Zensho)
Performed according to the description on pages 168 to 178.

For each of the obtained samples, a compact disk signal was recorded by a laser having a wavelength of 780 nm and 7 mW, and then reproduced by a commercially available compact disk player.

As a result, the S / N ratio was high and good reproduction could be performed.

Next, several sample pieces were prepared from one optical recording disk after recording, and the protective film and the reflective layer were separated from each sample.

 Next, the surface of the substrate was washed with methanol.

In this case, two types of cleaning conditions were used: weak cleaning in which the solvent was slightly shaken in a solvent, and strong cleaning in which ultrasonic cleaning was performed.

Then, the thickness in the groove of the substrate was determined from a scanning tunneling microscope (STM) output image of the cleaned substrate surface.

As a result, in the case of the sample subjected to ultrasonic cleaning having a strong cleaning power, the pit portion of the substrate was flat or dented.

On the other hand, the pit portion of the substrate of the sample which was washed with weak washing power was raised.

From these results, the portion of the sample that was washed with a weak detergency appeared to be raised, and the material of the recording layer, such as the dye, was decomposed and deteriorated by heat, that is, the decomposed product of the recording layer material with reduced solubility. It is considered to be a layer containing.

In fact, the residue after washing was measured by liquid chromatography, absorption spectrum, FTIR, MAS, etc.
It was confirmed that the substrate material was not included.

Then, for each sample, irradiate the Xe lamp through the substrate, the reflectivity at 780 nm in the initial and after 20 hours irradiation R ₀ ,
R was measured, and (1-R) / (1-R ₀ ) was calculated to evaluate the photobleaching property.

 Table 2 shows the results.

From the above, the effect of the present invention is clear.

Example 2 On a polycarbonate substrate, recording layers Nos. 4 to 6 shown in Table 3 below were provided at 800 °.

Table 4 shows the deterioration of the reflectance 20 hours after irradiation with the Xe lamp as light resistance.

Example 3 In Example 2, the recording layers were changed to recording layers No. 7 to No. 7 in Table 5 below.
When the result was changed to 9, the results shown in Table 6 were obtained.

From the above, the effect of the present invention is clear.

Good S / N ratio even for media with air sandwich structure
A ratio could be obtained.

<Effects> According to the present invention, the light resistance of the recording layer is extremely high, the reproduction deterioration of the medium is remarkably reduced, the light stability is extremely high, and the recording / reproduction in the CD standard is excellent. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing a contact type optical recording medium according to the present invention. DESCRIPTION OF SYMBOLS 1 ... optical recording medium 2 ... substrate 21 ... land portion 23 ... groove 3 ... recording layer 4 ... reflection layer 5 ... protective film 6 ... pit portion 61 ... decomposition layer 63 ... … Void

Continuation of front page (72) Inventor Noriyoshi Nanba 1-1-13 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-59-124895 (JP, A)

Claims (3)

(57) [Claims] 1. A substrate comprising a light absorbing dye having an absorption maximum at 600 to 900 nm and an azo dye having an absorption maximum at 350 to 600 nm on a substrate, wherein the light absorbing dye has a condensed ring. It has two or more kinds of cyanine dyes having a good indolenine ring, and has a recording layer having an extinction coefficient k of 0.05 to 0.2 at a recording light and a reproduction light wavelength of 700 to 900 nm. An optical recording medium having a protective layer laminated thereon. 2. The optical recording medium according to claim 1, wherein said recording layer further contains a quencher. 3. An optical recording method for irradiating an optical recording medium according to claim 1 or 2 with recording light to perform recording.