JP3451714B2 - Optical recording medium and optical recording / reproducing device. - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to optical information recording,
The present invention relates to an optical recording medium and an optical recording / reproducing apparatus for reproduction, and particularly to improvement of an optical recording medium containing an organic dye as a recording material.

[0002]

2. Description of the Related Art An optical recording medium for recording / reproducing information by irradiating a laser beam can have a narrower track width than a magnetic recording medium and enables high density recording, so that a large amount of information can be recorded. Received attention as a storage medium for storage,
Research is being actively conducted to improve the amount of recorded information.

Generally, as a laser beam for recording and reproducing on such an optical recording medium, a laser beam in a red to infrared region is used, and a recording medium corresponding thereto is widely spread. For example, a write-once type optical recording medium (so-called CDW
An example is a disc-shaped optical recording medium that can be written by a user, such as O: CD write once).

This CDWO has a structure in which a recording layer made of, for example, an organic dye is formed on a substrate, and signal recording is usually performed in a heat mode. That is, when the recording layer is irradiated with laser light, the energy of light is converted into heat by the light absorption of the organic dye, and the generated heat forms pits. Then, this pit is detected by the difference in reflectance between the portion where the pit is formed and the portion where the pit is not formed when the laser light is irradiated.

[0005]

By the way, the conventional CD
In WO, the wavelengths of the recording laser light and the reproducing laser light are the same, but in this case, if reproduction is carried out for a long period of time, recording pits will be destroyed or the recording layer material will be photo-degraded by the reproducing laser light. There is a fear of.

In order to prevent the destruction of the recording pits and the optical deterioration of the recording layer material due to the reproducing laser light, it is desirable that the wavelengths of the recording laser light and the reproducing laser light be different from each other.

Further, in the laser light, the minimum diameter of the laser spot depends on its wavelength, and the shorter the wavelength of the laser light is, the smaller the laser spot can be made. Therefore, there is a limitation in reducing the diameter of the laser spot with laser light having a long wavelength in the red to infrared region, and in order to increase the amount of information recorded in a certain area, a so-called super-resolution technique is required. .

In order to increase the amount of recorded information without such a device, the laser light is, for example, in the blue light region (wavelength 400-400).
It is necessary to shorten the wavelength to 500 nm).

Further, the conventional CDWO has low sensitivity, and higher sensitivity is desired in order to cope with high-speed recording / reproduction.

That is, in the CDWO, the wavelengths of the recording laser light and the reproducing laser light are made different in order to improve reliability and achieve high-density recording, and the wavelength of the laser light is shortened to, for example, the blue light region. The problem is to raise the sensitivity of the recording layer.

Porphyrin is one of the materials that can solve these problems. Porphyrin is a metal complex having a structure in which atomic groups are coordinated to a central metal and contains at least 38 n-electrons (the number of these n-electrons is increased by the substituent).

This porphyrin has an absorption band called a Soret band (soret band) derived from its 16-membered ring (18 n-electron system) on the short wavelength side in the molecular absorption spectrum. This Soret band has a very large molecular extinction coefficient, which is said to be several hundreds of thousands, and high sensitivity optical recording in the blue light region is possible by utilizing this large absorption band.

In the recording layer using this porphyrin, it has been confirmed that by making the wavelengths of the recording laser beam and the reproducing laser beam different, it is possible to reproduce signals with a high degree of modulation without destruction of recording pits. Is expected as a recording material for high-density recording with a high recording efficiency.

However, porphyrin is easy to crystallize due to the symmetry of its structure and is difficult to dissolve in a solvent. For this reason, it is difficult to spin coat as a solution. Therefore, when forming a film as a recording layer, it is necessary to use a vacuum deposition method that requires a large-scale device such as a vacuum device. Therefore, there is a problem that it is disadvantageous in improving productivity.

Therefore, the present invention has been proposed in view of such a conventional situation, and enables high-sensitivity optical recording in the blue light region, and a signal with a high modulation degree without destruction of recording pits. An object of the present invention is to provide an optical recording medium that can be reproduced and can form a recording layer by a spin coating method, and an optical recording / reproducing apparatus to which the optical recording medium is applied.

[0016]

In order to achieve the above object, the optical recording medium of the present invention comprises a transparent substrate on which a recording layer capable of optically recording and reproducing information is formed. The recording layer is composed of a porphyrin derivative represented by Chemical formula 5 and a polymer having a side chain having a molecular structure having a coordination ability with respect to the porphyrin derivative, and the porphyrin derivative is tetrabenzoporphine represented by Chemical formula 6. The above-mentioned tetrabenzoporphine is a zinc complex.

[0017]

[Chemical 5]

[0018]

[Chemical 6]

The optical recording medium to which the present invention is applied has a structure as shown in FIG. 1, for example. That is,
The recording layer 2 and the reflective layer 3 are sequentially formed on the substrate 1, and the protective layer 4 is further formed thereon. In this optical recording medium, recording is performed by a heat mode method in which pits are formed by heat generated when the recording layer 2 is irradiated with the laser beam 5.

In the present invention, the recording layer of such an optical recording medium is composed of a porphyrin derivative and a polymer having a molecular structure having a coordination ability in its side chain.

The porphyrin derivative is represented by the structural formula of the above chemical formula 5, and has a strong and sharp absorption band called a Soret band in the blue light region of wavelength 400 to 500 nm.

In the optical recording layer containing the porphyrin derivative, high sensitivity optical recording in the blue light region is possible by utilizing this large absorption band. Further, by making the wavelengths of the recording laser beam and the reproducing laser beam different, it is possible to reproduce a signal with a high degree of modulation without destroying the recording pits. Therefore, highly reliable high density recording can be achieved.

In the present invention, the optical recording layer is composed of such a porphyrin derivative and a polymer having a molecular structure having a coordination ability in its side chain. This is to enable the formation of the recording layer by the spin coating method.

That is, the porphyrin derivative is liable to crystallize due to the symmetry of its structure and is difficult to dissolve in the solvent.

Therefore, when this porphyrin derivative is dissolved in a solvent (organic solvent having a somewhat low boiling point) together with a polymer having a molecular structure having a coordinating ability in its side chain, the porphyrin derivative is well dissolved without crystallization. It dissolves in nature. As a result, the prepared dye solution can be spin-coated on the substrate, and a recording layer having excellent dispersibility without forming a stack of porphyrins is formed.

Further, in the recording layer, the side chain of each polymer is coordinated with the central metal of the porphyrin derivative, which shifts the absorption wavelength of the Soret band to the longer wavelength side. Therefore, writing is possible even at a wavelength at which the porphyrin derivative alone has almost no absorption.

That is, it is well known that when the ligand is coordinated to the central metal of the porphyrin derivative, the ultraviolet-visible absorption spectrum changes. The change is particularly remarkable in the above-mentioned Soret band, the Soret band is slightly shifted to the longer wavelength side, and the molecular absorption coefficient of the Soret band is increased. Therefore, in the present invention, as a porphyrin derivative, a tetrabenzoporphyrin zinc complex represented by Chemical formula 7 in which Bn to Bn + 1 (n: 1, 3, 5, 7) of Chemical formula 3 is cyclically bonded by C ₄ H ₄ is used. To use.

[0028]

[Chemical 7]

From the above, in the recording layer composed of the porphyrin derivative of the present invention and the polymer having a molecular structure having a coordinating ability in the side chain, the ligand of such a porphyrin metal complex is coordinated. By utilizing the long wavelength shift of the Soret band and the increase of the molecular extinction coefficient, it is possible to write even at a wavelength that has almost no absorption with the porphyrin derivative alone, and it is possible to increase the degree of freedom in selecting the laser light wavelength. Effect is obtained.

As the polymer, a polymer having a side chain capable of coordinating to the central metal of the porphyrin derivative, for example, a polymer having a side chain of an imidazole derivative, a pyridine derivative, a quinoline derivative, or a phenol derivative is referred to as a porphyrin derivative. It is desirable to select in consideration of the compatibility of.

The composition ratio of the porphyrin derivative to the polymer is preferably set so that the monomer constituting the polymer is present in a molar ratio of 50 times or more that of the porphyrin derivative. By mixing the porphyrin derivative and the polymer at this composition ratio, the porphyrin can be favorably dispersed in the recording layer without stacking. The optimum composition ratio varies slightly depending on the types of polymer and porphyrin derivative used. When polyvinyl pyridine is used as the polymer, it is preferable to set the composition ratio so that the vinyl pyridine monomer is present in a molar ratio of 67 times or more with respect to the porphyrin derivative.

The ratio of the monomer having the above-mentioned coordination ability to the whole polymer is preferably 50% or more in terms of molar ratio. A polymer containing a monomer having a coordinating ability in this range interacts well with porphyrin as a ligand, shifts the Soret band to a long wavelength, and increases the molecular extinction coefficient.

In the recording layer, in addition to the porphyrin derivative and the polymer, hindered amines, nickel complexes and the like are used in an amount of 30 parts by weight or less, preferably 0.1 to 10 parts by weight for the purpose of improving light resistance. Part may be added.

As the transparent substrate on which the recording layer as described above is formed, those used for ordinary optical recording media can be used, and examples thereof include glass, polycarbonate (PC),
Examples thereof include polyethylene terephthalate (PET).

As the reflective layer, those used in ordinary optical recording media can be used, and examples thereof include a vapor deposited film of aluminum and a vapor deposited film of gold.

The optical recording medium of the present invention may be provided with a lubricating layer and a protective layer in order to improve running characteristics, light resistance, chemical resistance and abrasion resistance. For example, as the protective layer, an ultraviolet curable film obtained by spin-coating an ultraviolet curable resin (for example, trade name SD17, manufactured by Dainippon Ink and Chemicals, Inc.) and curing by ultraviolet irradiation is suitable.

Recording and reproduction on such an optical recording medium are performed by an optical pickup device as shown in FIG.

That is, this optical pickup device is
An optical disk 18 for recording / reproducing is opposed to the objective lens 14 and includes a laser light source 11, a collimator lens 12, a shaping prism 13, an objective lens 14, a quarter wavelength plate 15, a polarization beam splitter 16, and a photodetector 17. Are arranged.

For recording with this optical pickup device, the laser light L diverged from the laser light source 11 is condensed into a circular shape by passing through the collimator lens 12, the shaping prism 13, and the objective lens 14, and the objective lens 13 is formed. This is performed by irradiating the optical discs 18 arranged so as to face each other. The optical disc 18 irradiated with the circularly focused laser light,
The energy of light is converted into heat by the light absorption of the dye contained in the recording layer, and the generated heat forms pits.

For reproduction, similarly, a circularly focused laser beam is applied to the optical disc 18, and the optical disc 1 is reproduced.
The reflected light reflected from No. 8 is guided to the photodetector 17 by the quarter-wave plate 15 and the polarization beam splitter 16, and this photodetector 17 detects the change in the amount of light. Since the reflectance of the optical disc 18 differs between the portion where the pit is formed and the portion where the pit is not formed, the presence or absence of the pit can be detected by the change in the reflected light amount.

[0041]

The recording layer made of a polymer having a molecular structure having a coordinating ability with a porphyrin derivative in the side chain has a strong sharp absorption band in the blue light region of 400 to 500 nm. Optical recording with high sensitivity is performed in the blue light region. In addition, by making the wavelengths of the recording laser light and the reproducing laser light different from each other, it is possible to reproduce a signal with a high degree of modulation without destroying recording pits.

When the porphyrin derivative is dissolved in a solvent together with a polymer having a molecular structure having a coordinating ability in its side chain, it is dissolved with good solubility without crystallization.
Therefore, the recording layer can be formed by the spin coating method instead of the vacuum deposition method which requires a large-scale device.

Further, in the recording layer, the side chain of each polymer is coordinated with the central metal of the porphyrin derivative, which shifts the absorption wavelength of the Soret band to the longer wavelength side. Therefore, writing is possible even at a wavelength at which porphyrin alone has almost no absorption.

[0044]

EXAMPLES Preferred examples of the present invention will be described based on experimental results.

The transparent substrate, recording layer material and reflective layer material used in this example are shown below. An optical recording medium was produced using these materials.

Substrate: Slide glass (manufactured by Matsunami Glass Co., Ltd., but cleaned in the order of disposer liquid, mixed acid, and millipore water) Recording layer material: Porphyrin derivative: tetraphenyltetrabenzoporphine zinc complex (Zn [TPTBT]; molecular weight 877) ) Polymer: poly-4-vinylpyridine (P-4-Vip
y; manufactured by POLYSCIENCES, vinyl pyridine monomer molecular weight 105) The structure of poly-4-vinyl pyridine is shown in Chemical formula 8.

[0047]

[Chemical 8]

Reflective Layer Material: Au First, a porphyrin derivative and a polymer were dissolved in chloroform at a weight ratio shown in Table 1 to prepare a dye solution.

This dye solution was applied to a spinner (MIKAS
(Manufactured by Company A) was spin-coated on the substrate at a rotation speed of 1000 rpm. Then, the substrate coated with this dye solution was left in a vacuum oven at a temperature of 60 ° C. for one day to completely remove the solvent and form a recording layer.

Then, a reflective layer is formed by vapor-depositing gold on this recording layer, and an optical recording medium (sample disks 1 to 1) is formed.
A sample disk 7) was produced.

Ultraviolet-visible absorption spectra of the thus prepared sample disks 1 to 7 were observed. Then, the maximum absorption wavelength λmax and the half-value width at λmax were measured, and the degree of shift of the maximum absorption wavelength λmax due to the dispersion state of the tetraphenyltetrabenzoporphine zinc complex and the coordination of the side chain of the polymer was evaluated.

Maximum absorption wavelength λma of each sample disk
x is shown in Table 1 together with the composition of the dye solution.

[0053]

[Table 1]

FIG. 3 shows the relationship between the molar ratio of the monomer constituting the polymer to the porphyrin derivative and the maximum absorption wavelength λmax. FIG. 3 shows the relationship between the molar ratio of the monomer constituting the polymer to the porphyrin derivative and the half-width at λmax. 4 shows. Further, for reference, an ultraviolet-visible absorption spectrum of a sample disk having a recording layer in which porphyrin is dispersed in a polymer having no molecule having a coordinating ability in the side chain is shown in FIG. The ultraviolet-visible absorption spectrum of the sample disk 6 in which the porphyrin derivative is contained in the polymer having the molecule is shown in FIG.

The dispersed state can be evaluated based on the following phenomenon due to the aggregation of molecules. That is, generally, the UV-visible absorption spectrum shows the molecule alone (in a dilute solution, etc.).
There is a difference between the case where the measurement is made in step 1 and the case where the measurement is made in the molecular aggregate (solid film etc.). The spectrum of a molecular aggregate is broader than the spectrum of a single molecule because a new vibration level is generated due to the interaction between molecules. Furthermore, the spectrum of the molecular aggregate is usually shifted to the longer wavelength side than the spectrum of the molecule alone.

Therefore, the dispersion state of the porphyrin derivative is reflected in the maximum absorption wavelengths λmax and the full width at half maximum of λmax. That is, in order to improve the dispersion state of the porphyrin derivative, the maximum absorption wavelength λmax is shifted to the short wavelength side, and the half width at λmax is narrowed.

From the viewpoint of the influence of the dispersion state on the spectrum and the long wavelength shift of the Soret band due to the coordination of the ligand, first, referring to FIG. 3, the maximum absorption wavelength λma
In the range where the composition ratio of the polymer is small, x once shifts to the long wavelength side and then to the short wavelength side as the composition ratio of the polymer increases. Then, it becomes stable when the molar ratio of the monomer constituting the polymer to the porphyrin derivative becomes 50 or more. The shift of the maximum absorption wavelength λmax to the longer wavelength side with the increase of the polymer composition ratio is due to the coordination of the polymer with the porphyrin derivative,
The shift to the shorter wavelength side is due to the improved dispersibility of the porphyrin derivative.

On the other hand, referring to FIG. 4, the full width at half maximum at λmax becomes narrower as the composition ratio of the polymer increases, and becomes almost at a molar ratio of the monomer constituting the polymer to the porphyrin derivative of 50 or more. Be stable. The narrowing change of the full width at half maximum with the increase of the polymer composition ratio is mainly due to the improvement of the dispersibility of the porphyrin derivative.

From the above results, it is understood that when the recording layer is made of a polymer having a coordination ability with the porphyrin derivative, the dispersibility of the porphyrin derivative is improved and a recording layer having no stack can be obtained. Further, it is understood that the polymer is coordinated to the porphyrin derivative, and this changes the ultraviolet-visible absorption spectrum. Since the maximum absorption wavelengths λmax and the change in the half width at λmax are saturated when the molar ratio of the monomer constituting the polymer to the porphyrin derivative reaches 50, the composition ratio of the porphyrin derivative and the polymer is It is understood that the molar ratio of the monomer constituting the polymer to the porphyrin derivative may be set to 50 or more.

Next, with respect to the sample disk 6 of the above optical recording medium, the change of the reflection spectrum due to writing was examined.

Confirmation of writing and pit formation,
To measure the reflection spectrum of the recording layer by forming pits, as shown in FIG. , Microspectrophotometer 2
6 and a CCD monitor 27.

Here, the wavelength of the Ar laser is 488 nm and the laser output is 14 mW. The reflection spectrum before laser light irradiation and the reflection spectrum after laser light irradiation are also shown in FIG.

From FIG. 8, the reflection spectrum changes before and after laser irradiation, and the recording layer made of tetraphenyltetrabenzoporphine and poly-4-vinylpyridine is
It is confirmed that writing is possible by irradiation with laser light having a wavelength of 488 nm.

Incidentally, the sample disc having a recording layer in which porphyrin is dispersed in a polymer having no molecule having a coordinating ability in the side chain has almost no absorption at 488 nm as shown in FIG. Therefore, the wavelength is 488 nm
It is impossible to write with the laser light.

[0065]

As is apparent from the above description, in the present invention, the recording layer is composed of a porphyrin derivative and a polymer having a molecular structure having a coordinating ability in its side chain, and the porphyrin derivative is tetrabenzoporphine. And the tetrabenzoporphine is a zinc complex,
The polymer is coordinated to the porphine derivative and crystallization is suppressed, so that the porphyrin derivative can be dissolved in the solvent. Accordingly, in the present invention, the recording layer can be formed by the spin coating method, and the porphyrin derivative is uniformly dispersed in the recording layer, so that highly reliable and high density recording can be performed.

Further, according to the present invention, by using the porphyrin derivative, highly sensitive optical recording in the blue light region is possible. Further, according to the present invention, it is possible to reproduce a signal with a high degree of modulation without destroying recording pits. Further, in the present invention, writing can be performed at a wavelength at which the porphyrin derivative alone has almost no absorption. Therefore, the present invention can greatly contribute to the improvement of the productivity of the optical recording medium.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration example of an optical recording medium to which the present invention is applied.

FIG. 2 is a schematic diagram showing a configuration example of a recording / reproducing apparatus for performing recording / reproducing with respect to an optical recording medium.

FIG. 3 is a characteristic diagram showing a relationship between a polymer composition ratio of a recording layer and a maximum absorption wavelength λmax of an ultraviolet-visible absorption spectrum.

FIG. 4 is a characteristic diagram showing the relationship between the polymer composition ratio of the recording layer and the half-value width at the maximum absorption wavelength λmax of the ultraviolet-visible absorption spectrum.

FIG. 5 is a characteristic diagram showing an ultraviolet-visible absorption spectrum of an optical recording medium having a recording layer in which porphyrin is dispersed in a polymer having no molecule having a coordinating ability in a side chain.

FIG. 6 is a characteristic diagram showing an ultraviolet-visible absorption spectrum of an optical recording medium having a recording layer in which porphyrin is dispersed in a polymer having a molecule having a coordination ability in a side chain.

FIG. 7 is a schematic diagram showing the configuration of an evaluation system used to evaluate the state of writing pits on an optical recording medium.

FIG. 8 is a characteristic diagram also showing reflection spectra before and after writing of an optical recording medium in which a polymer is contained in a recording layer.

[Explanation of symbols]

1 substrate 2 recording layers 3 reflective layer 4 protective layer

Continuation of the front page (56) Reference JP-A-61-232448 (JP, A) JP-A-4-339865 (JP, A) JP-A-1-294791 (JP, A) JP-A-2-230530 (JP , A) JP 63-160891 (JP, A) JP 7-141642 (JP, A) JP 6-1073 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) B41M 5/26 G11B 7/24 516 CAPLUS (STN) REGISTRY (STN) MARPAT (STN)

Claims (3)

(57) [Claims] 1. A recording layer capable of optically recording and reproducing information is formed on a transparent substrate, and the recording layer comprises a porphyrin derivative represented by Chemical formula 1.
Made of a polymer having a molecular structure with a coordination ability with respect to the porphyrin derivative in the side chain, the porphyrin derived
The body is tetrabenzoporphine represented by Chemical formula 2,
An optical recording medium characterized in that tetrabenzoporphine is a zinc complex . [Chemical 1] [Chemical 2] 2. The optical recording medium according to claim 1, wherein recording is performed at a recording wavelength of 400 to 500 nm. 3. An optical recording / reproducing apparatus comprising an optical pickup device comprising a laser light source, a lens and a photodetector, and an optical recording medium arranged facing the lens of the optical pickup device. A polymer having a laser wavelength of 400 to 500 nm, wherein the optical recording medium has, on a transparent substrate, a porphyrin derivative represented by Chemical formula 3 and a side chain having a molecular structure having a coordination ability with respect to the porphyrin derivative. Becomes and above
Note that the porphyrin derivative is represented by the chemical formula 4.
Is a ruffin, and the tetrabenzoporphine is a zinc complex.
An optical recording / reproducing device characterized by being a body . [Chemical 3] [Chemical 4]