JP2778132B2 - Optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel optical recording medium using a thermally decomposable substance having no absorption in a laser wavelength range as a recording material.

[Summary of the Invention]

The present invention, by laminating a recording layer containing a pyrolytic substance and a metal layer that absorbs laser light to some extent on a substrate, has a high reflectance in a semiconductor laser wavelength region used at the time of signal reading, Another object is to provide an optical recording medium having excellent recording sensitivity.

[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 is capable of recording / reproducing in a non-contact manner, achieving a recording density one order of magnitude higher than that of a magnetic recording system,
It has a number of advantages such as being able to support each type of memory of read-only type, write-once type, and rewritable type. As a method for realizing inexpensive large-capacity files, a wide range of applications from industrial use to consumer use 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 a recording material absorbing light energy and converting it into heat energy is used. The irreversible physical change includes a change in the shape of the recording layer (formation of pits), a change in surface properties, a change in the crystalline state, and the like.

Most of write-once optical recording media which have been put to practical use so far 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 organic dye must have a large absorption in the near infrared region, which is a wavelength range of a semiconductor laser used for recording and reproduction. , Metal phthalocyanine dyes, naphthoquinone dyes and the like are known.

[Problems to be solved by the invention]

By the way, in order to achieve desirable recording / reproducing characteristics in an optical recording medium, it is necessary to satisfy the following conditions as physical properties of a 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, it is necessary that the change in reflectance before and after recording is large, the shape of the formed pits is smooth, the generation of noise is small, and the like. As described above, although there are various desirable conditions, high absorption and high reflectance are the most basic optical characteristics.

When considering that an optical recording medium using an organic dye as a recording material is reproduced by, for example, a reproducing apparatus for reproducing an optical disk (a so-called compact disk) provided with an aluminum reflective film on a substrate having pits formed thereon, at least the reflectance is required. Must be as high as the current compact disc value (more than 70% at 780nm). 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. Furthermore, unlike a read-only type compact disc or the like, a write-once type optical recording medium has a problem that if only a high reflectance is sought, recording sensitivity is impaired. In other words, in order to achieve high reflectance at a certain wavelength, the light absorptance at that wavelength must necessarily be low, but if the light absorptivity is low, an irreversible physical change can be effectively generated. become unable.

As a technique for increasing the reflectance, it is conceivable to laminate a high-reflectance metal reflective layer on the light-absorbing / pyrolyzing dye layer. The requirements for the dye are basically the same as those described above, and the reflectivity of the optical recording medium greatly depends on this dye layer.

To solve this problem, even if the absorbed light energy is small, it can be efficiently converted to heat energy,
One must search for organic dyes that cause irreversible physical changes.

From these, it is very difficult to find a dye having good properties as a recording material, such as being more resistant to light degradation, having excellent weather resistance, and having high solubility in general-purpose solvents.

Therefore, the present invention has been proposed in view of such conventional circumstances, and the development of an optical recording medium having a large reflectivity in the wavelength range of a semiconductor laser and in which a physical change is efficiently generated by a laser beam is proposed. An object of the present invention is to provide an optical recording medium having excellent recording characteristics and reproduction characteristics.

Another object of the present invention is to provide an optical recording medium that can be easily prepared by expanding the range of usable recording materials by relaxing the requirements for the recording material.

[Means for solving the problem]

The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and as a result, by using the heat generation of the metal layer to cause a physical change of the recording layer, the optical properties of the recording material used are improved. It has been found that the conditions can be relaxed and the recording / reproducing characteristics can be improved.

The optical recording medium of the present invention has been completed based on such findings, and has a recording medium containing a pyrolyzable substance which has no absorption in a laser wavelength range and is decomposed and / or degraded by heating on a substrate. Layer and reflectivity at the laser wavelength
70% or more and 85% or less of metal layers are sequentially laminated.

That is, as shown in FIG. 1, for example, as shown in FIG. 1, the optical recording medium of the present invention has a recording layer on which a physical change is caused by heat on a transparent substrate (1) on which a pre-groove (1a) is formed. (2) and a metal layer (3) which secures the reflectance with respect to the laser beam and absorbs a part thereof and generates heat, which are sequentially laminated. On the metal layer (3),
Further, if necessary, a protective film (4) made of an ultraviolet curable resin, a thermosetting resin, or the like may be provided.

The material of the substrate (1) is not particularly limited as long as it is used for an ordinary optical recording medium. For example, plastics such as polycarbonate and acrylic, glass and the like are suitable.

Further, the metal layer (3) provided on the recording layer (2) has a high reflectivity to some extent, and needs to absorb a part of the laser light for photothermal conversion. It is necessary to have absorption.
Therefore, the reflectivity of the metal layer (3) in the laser wavelength range (for example, a wavelength of 780 nm) is set to 70% or more and 85% or less in order to satisfy both of them. The metal layer (3)
If the reflectance is less than 70%, it is difficult to ensure a reflectance that can maintain compatibility with a compact disc. Conversely, if the reflectance of the metal layer (3) exceeds 85%, the amount of light absorbed is reduced, and the heat generation becomes insufficient, resulting in a decrease in sensitivity.

To set the reflectance of the metal layer (3) in the above range,
A metal or alloy exhibiting a reflectance within the above range may be used. It is possible to use a dielectric multi-layer film instead of metal. In particular, when an alloy is used, the reflectance can be controlled by changing the composition, which is preferable.

The thickness of the metal layer (3) depends on the problem of solvent resistance when the protective layer (4) is further spin-coated on the metal layer (3), the amount of light absorbed by the metal layer (3), From the viewpoint of fabrication and the like, it is necessary that the thickness be 30 nm or more. If the film thickness is too small, the amount of laser light transmitted through the metal layer (3) increases, and the light may not be absorbed effectively and the sensitivity may be reduced. (3) There is a possibility that the device itself will be broken. However, if the film thickness is too large, the amount of heat transmitted through the metal layer (3) to escape increases, and the sensitivity also decreases. In consideration of these, the film thickness is preferably about 50 to 70 nm.

On the other hand, the recording layer (2) causes a physical change such as decomposition and alteration due to heat generation of the metal layer (3), and a thermal decomposition material having no absorption in a laser wavelength region is used as a recording material. It shall be.

In the complex refractive index (n ^* = n-ik; i is an imaginary unit) of the thermal decomposition substance used for the recording layer (2), there is no restriction on the real part n (so-called refractive index). However, when recording / reproducing, the pre-groove (1a) provided on the substrate (1)
It is preferable that the distance from the refractive index (about 1.5) of a resin such as polycarbonate, which is a material of the substrate (1), be as small as possible for easy tracking. On the other hand, for the imaginary part k, the second
As shown in the figure, the reflectance is determined by the reflectance of the metal layer (3).
The range of the value satisfying 70% or more changes, and it is necessary to enter the shaded region in FIG.

Further, the pyrolyzed substance is deteriorated and decomposed due to a rapid rise in temperature due to laser irradiation, and gas is generated, so that the recording layer (2) must be significantly deformed. So 10
It is desirable to use one that generates gas by decomposition or vaporization in the range of 0 to 300 ° C. Needless to say, it is desirable that the recording material has excellent weather resistance as in a general recording material.

Examples of the thermally decomposable substance that satisfies such conditions and can be used in the recording layer (2) include the following substances in addition to cyanine dyes (having no absorption at the laser wavelength), coumarin dyes, and the like. .

These thermal decomposition substances may be used alone as the recording layer (2), or may be mixed with some kind of polymer material to form a film to form the recording layer (2).

The thickness of the recording layer (2) is preferably set according to the reflectance of the metal layer (3). This is because even if the pyrolysis substance satisfies the above complex refractive index condition, the recording layer (2)
This is because the reflectivity may be less than 70% depending on the film thickness. The thickness D of the recording layer (2) is D
= Λ / 2n, the reflectance becomes 70% or more. However, depending on the reflectance of the metal layer (3), the reflectance may be 70% or more even if the recording layer (2) has any thickness. is there.

[Action]

In the optical recording medium of the present invention, the reflectance of the metal layer is 85.
% Or less, the metal layer absorbs laser light to some extent and generates heat. Then, due to the heat generated by the metal layer, the thermally decomposed substance contained in the recording layer is decomposed and deteriorated to cause a physical change, and information is recorded.

Here, the thermal decomposition material has almost no absorption in the laser wavelength range, and the reflectance of the metal layer is 70% or more, so that a reflectance of 70% or more is ensured. Will be kept.

〔Example〕

Hereinafter, the present invention will be described based on specific experimental results.

In this example, a cyanine dye (manufactured by Nippon Kogaku Dye Laboratories, trade name NK529) was used as the pyrolysis substance, and gold and gold were used for the metal layer.
A palladium alloy was used. The structural formula of the cyanine dye used is as follows.

This cyanine dye is a semiconductor laser wavelength (780nm)
Has a complex refractive index of 2.36 to 0.02i, which indicates that the semiconductor laser has almost no absorption in the wavelength region. The reflectivity of the gold / palladium alloy in the semiconductor laser wavelength range was 84%, which satisfied the conditions specified in the present invention.

A protective layer was provided on the metal layer, and the protective layer was made of an ultraviolet curable resin (Dainippon Ink and Chemicals, trade name: SD-17)
Was used.

The sample is a polycarbonate substrate with a grave (diameter
8 cm), a cyanine dye (NK529) was spin-coated, a gold / palladium alloy film was formed thereon by a sputtering method, and a UV-curable resin was spin-coated thereon and then cured.

The cyanine dye (NK529) is dissolved in a solvent (3-hydroxy-
(3-methyl-2-butanone) was dissolved in about 4% and spin-coated. Spin coating speed is 1000rpm
Before and after. For gold / palladium alloy, 50
The samples were laminated with a thickness of nm, 60 nm, and 70 nm to prepare three types of samples. The ultraviolet curable resin was spin-coated at 1600 rpm and cured with a 2 kW mercury lamp.

FIG. 3 shows the result of performing static recording on the sample thus manufactured. The horizontal axis in FIG. 3 is the pulse width of the recording laser light, and the vertical axis is the modulation degree. Note that the intensity of the recording laser beam was fixed at 8 mW. The numerical aperture NA of the lens used for reading is 0.6.

The line i in the figure is for a sample with a metal layer thickness of 50 nm, and the line ii
Represents a sample having a metal layer thickness of 60 nm, and line iii corresponds to a sample having a metal layer thickness of 70 nm.

Referring to FIG. 3, in each case, the pulse width is 1 μm.
It can be seen that a high degree of modulation can be obtained at s or more, and especially when the film thickness of gold / palladium is 60 nm, recording can be performed steeply from a pulse width of 0.4 μs.

Thus, the manufactured sample has high sensitivity as an optical recording medium and can perform recording with a high γ value.

〔The invention's effect〕

As is clear from the above description, since the optical recording medium of the present invention causes thermal decomposition and deterioration of the recording layer by utilizing the light absorption of the metal layer, there are restrictions on the recording material used for the recording layer. It is possible to provide an optical recording medium that can be relaxed, is easy to produce, and has high sensitivity.

Further, in the optical recording medium of the present invention, since the thermal decomposition substance contained in the recording layer has almost no absorption in the laser wavelength range, the reflectance is almost determined by the reflectance of the metal layer. It is possible to provide a write-once (write-once) optical recording medium which is compatible with the optical recording medium.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an essential part showing a configuration example of an optical recording medium to which the present invention is applied. FIG. 2 is a characteristic diagram showing a range of an imaginary part k of a complex refractive index of a pyrolytic substance that can be used for a recording layer in relation to a reflectance of a metal layer. FIG. 3 is a characteristic diagram showing the pulse width dependence of the modulation factor in the embodiment to which the present invention is applied. 1 ... substrate 2 ... recording layer 3 ... metal layer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 7/24

Claims (1)

(57) [Claims] A recording layer containing a thermal decomposition substance which has no absorption in a laser wavelength range and decomposes and / or changes by heating on a substrate; and a reflectance at a laser wavelength of 70% or more;
An optical recording medium in which 85% or less of metal layers are sequentially laminated.