JP3028520B2 - Optical information recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical information recording medium using an organic dye as a recording material, and more particularly to an improvement in the reflectance thereof.

[Summary of the Invention]

The present invention relates to an optical information recording medium in which an organic dye layer and a metal reflectivity are sequentially formed on a substrate.
By providing a cyanine dye having an absorption maximum in a wavelength region of -690 nm and providing the above-mentioned metal reflective layer, it is possible to provide an optical recording medium having a high reflectance in a semiconductor laser wavelength region to be used and also having excellent recording sensitivity. It is intended.

[Conventional technology]

2. Description of the Related Art In recent years, in the field of information recording, researches on optical information recording methods have been advanced in various places. This optical information recording system can perform recording and reproduction without contact, and can achieve a recording density that is at least an order of magnitude higher than magnetic recording media,
It has many advantages, such as being compatible with the read-only type, write-once type, and rewritable type memory types, and is expected to be used in a wide range of applications from industrial use to consumer use as a method that enables the realization of inexpensive large-capacity files. It is what is being done.

Of the above-mentioned memory forms, the write-once type is one in which recording and reproduction can be performed by an end user and cannot be erased, so that it is mainly used as a long-term data storage file. At the time of recording, a local irreversible physical change of the recording layer caused by the absorption of light energy by the recording material and conversion into heat energy is used. Known irreversible physical changes include a change in the shape of the recording layer (formation of pits), a change in surface properties, a change in the crystal state, and the like.

Most of write-once optical information recording media currently in practical use use a tellurium alloy or tellurium compound as a recording material. However, in recent years, organic dyes have attracted attention in place of these tellurium-based materials from the viewpoint of further improving mass productivity and economic efficiency of media. The above organic dyes need to show large absorption in the near-infrared region of semiconductor lasers used for recording / reproducing. Are known.

[Problems to be solved by the invention]

By the way, desirable recording and
In order to achieve reproduction characteristics, it is necessary to satisfy the following conditions as physical properties of the recording material. First, in order to obtain high recording sensitivity, it is necessary that the light absorption rate is high, the heat capacity is low, the thermal conductivity is low, and the thermal change for recording occurs at a relatively low temperature. On the other hand, in order to obtain high reproduction sensitivity, the reflectance change before and after recording is large, the shape of the formed pit is smooth,
It is necessary that noise generation is small. As described above, although there are various desirable conditions, high absorption and high reflectance are the most basic optical characteristics.

However, conventionally known organic dyes have a low reflectance of at most 30 to 40% when formed into a film, and cannot achieve a sufficient reproduction sensitivity. When considering that an optical information recording medium using an organic dye as a recording material is reproduced by a reproducing apparatus for reproducing a disk (a so-called compact disk) provided with an aluminum reflecting film on a substrate having pits formed thereon, at least the reflectance is considered. Must be as high as the current compact disc value (more than 70% at 780nm). However, unlike a read-only compact disc or the like, a write-once type optical information recording medium has a problem that recording sensitivity is impaired if only a high reflectance is pursued. In other words, in order to achieve high reflectance at a certain wavelength, the light absorption at that wavelength must be low, but if the light absorption is low, irreversible physical changes cannot be effectively generated. It is. In order to solve this problem, it is necessary to search for an organic dye that efficiently converts even a small amount of absorbed light energy into heat energy and causes irreversible physical change.

Therefore, an object of the present invention is to provide an optical information recording medium having excellent recording characteristics and reproducing characteristics.

[Means for solving the problem]

The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and as a result, 660 in a methanol solution as a recording material.
The inventors have found that the above object can be achieved by using a cyanine dye having an absorption maximum in a wavelength region of up to 690 nm and providing a metal reflective layer, thereby completing the present invention.

That is, the optical information recording medium according to the present invention is an optical information recording medium in which an organic dye layer and a metal reflection layer are sequentially formed on a substrate, and recording and reproduction are performed by a laser beam having a wavelength of 780 nm. Contains a cyanine dye having an absorption maximum in a wavelength range of 660 to 690 nm in a methanol solution, and has a reflectance of 70 for a laser beam having a wavelength of 780 nm.
% Or more.

First, as shown in FIG. 1, the configuration of the optical information recording medium of the present invention is such that a semiconductor laser beam is absorbed on a transparent substrate (1) on which a pre-group (guide groove) is formed as necessary. An organic dye layer (2) for performing light-to-heat conversion and a metal reflection layer (3) for increasing the reflectance are sequentially laminated. A protective film (4) made of an ultraviolet curable resin, a thermosetting resin, or the like may be further provided on the metal reflective layer (3) as needed.

The cyanine dye is a compound in which a heterocyclic ring is linked by a methine chain. The heterocycle includes, for example, a benzoindoline ring, a benzothiazoline ring, a naphthothiazoline ring and the like, and the methine chain is a pentamethine chain having 5 carbon atoms. Hereinafter, three typical general formulas of the organic dye used in the present invention are shown in order.

First, a cyanine dye having a benzoindoline ring is represented by the following general formula (I) It is represented by

In the formula, R ₁ represents an alkyl group having 1 to 20 carbon atoms, and R ₄ represents any one of a hydrogen atom, a halogen atom, an alkyl group, and an alkoxy group. R ₁ and R ₂ may be the same or different. The X is I ^-, Br ^-, Cl ^- halogen ion such as, ClO ₄ ^-, or represents any one of the substituted benzenesulfonic acid ion, Me represents a methyl group.

Next, a cyanine dye having a benzothiazoline ring is represented by the following general formula (II) The cyanine dye having a naphthothiazoline ring is represented by the following general formula (III) It is represented by

Here, in the formula, R ₂ represents an alkyl group having 1 to 20 carbon atoms, and R ₃ represents any one of a hydrogen atom, a halogen atom, an alkyl group, and an alkoxy group. R ₁ and R ₂ may be the same or different.

The heterocycle of these cyanine dyes is described in, for example,
-122577 or Japanese Patent Publication No. Sho 60-177089 can be synthesized, and the absorption maximum when measured in a methanol solution is 660 to 690.
It has in the wavelength region of nm. The above-mentioned wavelength range is set from the viewpoint of optimizing both the recording characteristics and the reproduction characteristics. If the absorption maximum exists in a region having a wavelength shorter than 660 nm, the cyanine dye cannot effectively absorb the energy of the recording light of 780 nm, so that the recording becomes impossible or the recording sensitivity is reduced, while a wavelength longer than 690 nm is used. If it exists in the region, the 780 nm reproduction light cannot be effectively reflected, and a high reflectance of 70% or more at 780 nm may not be obtained.

The organic dye layer containing a cyanine dye as described above,
Generally, it is formed on a substrate by applying a solution dissolved in an appropriate organic solvent. Its layer thickness is 600 ~ 2500Å
Is chosen. If the layer thickness is outside the above range, the recording / reproducing sensitivity, productivity, economy, etc. will be degraded. That is, if the layer thickness is smaller than the above range, the amount of change in the organic dye layer due to laser heat is small, and sufficient S / N cannot be obtained. When the layer thickness is larger than the above range, absorption increases, and as a result, at 780 nm, the absorption increases.
% Is not preferable because it is difficult to obtain a high reflectance of at least 100%. As the organic solvent, those that can dissolve the organic dye and do not damage the substrate are appropriately selected and used.

The substrate is not particularly limited as long as it is used for a usual optical information recording medium, and for example, plastics such as polycarbonate and acrylic, glass, and the like are suitable.

The metal reflective layer provided on the organic dye layer, 780n
A metal having a high reflectivity at m is applied by a vacuum thin film forming technique such as vacuum evaporation and sputtering.
Examples of the metal include Au, Cu, Al, and Ag. The thickness of the metal reflection layer is selected to be about 300 to 2000 mm. 300 layer thickness
If it is less than Å, the effect of increasing the reflectance of the optical information recording medium is insufficient, and the reflectance of 70% or more at a wavelength of 780 nm cannot be achieved. When the temperature exceeds 2000 mm, the laser heat absorbed by the organic dye layer is dissipated to the metal reflective layer with high thermal conductivity,
Further, since the thermal change of the organic dye layer is also suppressed, the recording sensitivity is reduced.

The overall thickness of the optical information recording medium of the present invention configured as described above can be set to 1.5 mm or less as in the case of a current compact disk or the like. Conventionally, for example, in an optical information recording medium in which a protective film is formed on an organic dye layer, a gap is provided between the organic dye layer and the protective film in order to prevent pit formation from being physically suppressed. That had been proposed. However, this would make the media too thick overall and would cause the current compact disc or CD-ROM
It is impossible to reproduce with some reproducing apparatuses, and the medium compatibility of the reproducing apparatus is narrowed. On the other hand, according to the present invention, good recording / reproduction can be performed even with the configuration shown in FIG. 1 due to the excellent characteristics of the cyanine dye used.

[Action]

The cyanine dye used as a recording material of the optical information recording medium in the present invention has an absorption maximum measured in a methanol solution in a wavelength region of 660 to 690 nm. Generally, the spectrum of the dye shows a broad absorption band to some extent, but in the case of the cyanine dye whose absorption maximum is within the above range, the wavelength of a typical semiconductor laser is 780n.
The vicinity of m corresponds to the end of the absorption band, and the absorption rate is low. However, due to its excellent light-to-heat conversion function, this cyanine dye effectively generates heat even with a small amount of light energy, and induces physical phenomena such as evaporation, sublimation, and aggregation. Thermal deformation is caused by the forward pressure exerted on the reflective layer. Therefore, high recording sensitivity can be achieved.

On the other hand, a low absorptance at 780 nm means a high reflectivity at this wavelength, and by providing a metal reflective layer to supplement the reflectivity, high-sensitivity reproduction is possible.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

First, a cyanine dye was synthesized. The present inventors have synthesized cyanine dyes (compounds A to C) as shown in Table 1 below. Here, a detailed synthesis method is omitted. Table 1 shows λ of Compounds A to C.
_{max is} also shown.

Using these compounds, an optical information recording medium was actually produced.

Example 1 4 parts by weight of the above compound A was dissolved in 100 parts by weight of diacetone alcohol, and this cyanine dye solution was filtered through a filter having a pore diameter of 0.3 μm, and then spin-coated on a polycarbonate substrate having a diameter of 130 mm and a thickness of 1.2 mm. It was applied to form an organic dye layer. The layer thickness of this organic dye layer after drying is 10
It was 00Å.

Next, on the organic dye layer, Au was deposited by a vacuum evaporation method.
A metal reflective layer was formed to a thickness of 600 mm. Further, after applying a solution of an ultraviolet curing resin (trade name: SD-17, manufactured by Dainippon Ink and Chemicals Co., Ltd.) on the metal reflective layer, the coating is completely cured by irradiation with ultraviolet light to form a protective film, and optical information recording is performed. Completed the medium.

Examples 2 and 3 The method described in Example 1 was followed except that an organic dye layer having a layer thickness shown in Table 2 below was formed using Compound B or Compound C instead of Compound A described above. Therefore, an optical information recording medium was created.

For each of these optical information recording media, the λ
The reflectance at _max and 780 nm was measured.

Table 2 below summarizes the measurement results for the optical information recording media prepared in Examples 1 to 3 described above.

In general, when this type of organic dye is formed as a solid thin film such as an organic dye layer, a phenomenon in which λ _max shifts to longer wavelengths than when measured in a solution state due to aggregation or association is observed. However, the wavelength still deviates from 780 nm, which is the wavelength of a semiconductor laser used for recording and reproduction, and both recording characteristics and reproduction characteristics can be achieved.
Each of these optical information recording media showed a high reflectance of 70% or more.

Next, when the recording / reproducing characteristics of the optical information recording media created in the examples were examined, it was found that these optical information recording media efficiently converted small light energy into heat energy and caused thermal deformation. all right. However, although light energy is low like this,
When the laser power was 6 mW or less, satisfactory recording was not performed, and it became clear that there was a clear threshold in the recording. This means that the thermal deformation of the substrate or the metal reflective layer does not easily change even if the laser beam is repeatedly irradiated at the time of reading, and from the viewpoint of improving the recording stability and the durability of the optical information recording medium. Is an extremely advantageous property.

〔The invention's effect〕

As is clear from the above description, when the present invention is applied, even if the absorbed light energy is small, the organic dye can efficiently convert it to heat energy, and the sufficient amount of light is absorbed between the exposed part and the non-exposed part. The substrate or the metal reflective layer is deformed so as to cause a large difference in reflectance. Moreover, since the reflectance of the optical information recording medium is maintained sufficiently large,
Improvements in recording sensitivity and reproduction sensitivity are achieved at the same time without sacrificing either one, and a highly reliable write-once optical information recording medium suitable for high-speed recording and high-density recording is provided.

Furthermore, good recording / reproducing characteristics can be obtained even if a metal reflective layer is directly laminated on the organic dye layer, so that the thickness of the optical information recording medium can be reduced to the current compact disc or CD-ROM.
, Etc., and it is also possible to play back with a common playback device.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part showing a configuration example of an optical information recording medium according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Organic dye layer 3 ... Metal reflective layer 4 ... Protective film

Continuation of front page (56) References JP-A-64-40388 (JP, A) JP-A-2-147286 (JP, A) JP-A-58-105442 (JP, A) JP-A-2-134290 (JP, A) , A) JP-A-1-232287 (JP, A) JP-A-62-262238 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/26

Claims (2)

(57) [Claims] An optical information recording medium in which an organic dye layer and a metal reflective layer are sequentially formed on a substrate, and recording and reproduction are performed with a laser beam having a wavelength of 780 nm, wherein the organic dye layer is 660 to 660 nm in a methanol solution. It has a maximum absorption in the wavelength region of 690 nm, contains a cyanine dye represented by any of the following formulas (I) to (III), and has a reflectance of 70% or more to a laser beam having a wavelength of 780 nm. Optical information recording medium. (Wherein, R ₁ and R ₂ each represent an alkyl group having 1 to 20 carbon atoms, and R ₃ and R ₄ represent any one of a hydrogen atom, a halogen atom, an alkyl group, and an alkoxy group. R ₁ and R ₂
May be the same or different. X represents one of a halogen ion, ClO ₄ ⁻ , and a substituted benzenesulfonic acid ion, and Me represents a methyl group. ) 2. The optical information recording medium according to claim 1, wherein said organic dye layer has a thickness of 600 to 2500 ° and said metal reflective layer has a thickness of 300 to 2000 °. .